SAFETY AND EFFICACY OF WHEY PROTEIN SUPPLEMENTATION IN TEENAGE ATHLETES

In addition to the physical aspects of training, young athletes are also mirroring the nutritional and supplementation practices of adult athletes. While research on the use of supplements among adult athletes is well known, few studies on supplement use by teenage athletes exist. Research has reported that between 22.3% to 71% of high school athletes use some form of supplementation, with whey protein being the most common. Despite the popularity of whey protein among teenage athletes, knowledge regarding its effects on health and performance in teenage athletes is currently insufficient. Therefore, the purpose of this study was to assess the safety of whey protein supplementation in relation to biomarkers of kidney functioning. A secondary purpose of this study was to investigate the effects of whey protein supplementation on body composition and athletic performance in teenage athletes. Ten healthy teenage participants (five boys and five girls) were matched according to body mass, height, tanner stage, age, and strength, and separated and randomly assigned in a double blind manner to either a 24g/d whey protein group (WP) (n = 5; age: 16 ± 1 y; Tanner: 4.2 ± 0.8; Height: 1.7 ± 0.1 m; Mass: 78.6 ± 23.4 kg; BF: 23.3 ± 11.2 %) or a 27 g/d carbohydrate control group (CG) (n = 5; age: 15.2 ± 1.6 y; Tanner: 4.6 ± 0.9; Height: 1.7 ± 0.1 m; Mass: 69.8 ± 15.4 kg; BF: 20.5 ± 10.1 %). Participants consumed their given supplement daily for four weeks. Biomarkers of kidney health, assessed via urinalysis, were collected at pre and post. At baseline and post, participants underwent athletic performance tests consisting of 1RM squat and bench press, vertical jump, and 5-10-5 agility run, and body composition testing. One-day diet logs were completed at baseline and post. Diets were analyzed for mean calorie, carbohydrate, protein, and fat intake. Participants were considered free-living and continued with their individual sport and resistance training programs. Baseline dependent variable differences between groups were compared using independent samples t-tests. Differences in athletic performance measures, body composition, and urinalysis measures were analyzed by a two-way mixed factorial (ANOVA). Significance was set at p ≤ 0.05 and values are presented as mean ± SD. There were no baseline differences (p ≥ 0.05) in age, height, tanner stage, body mass, vertical jump, 5-10-5 pro agility run, squat 1RM, bench press 1RM, PBF, LBM, BMD, or any urinalysis measure. Additionally, no baseline differences (p ≥ 0.05) were observed for mean calorie, carbohydrate, protein, or fat intake. No main effect (p ≥ 0.05) for time was revealed for VJ, 5-10-5 pro agility run, squat 1RM, or any body composition or urinalysis measure, but was revealed for bench press 1RM (p = 0.003). However, there was no group X time interaction was observed for any athletic performance, body composition, or urinalysis variable (p ≥ 0.05). To the best of our knowledge, this study is the first of its kind investigating the effects of whey protein on health and performance in teenage athletes. Results of this study suggest that short-term whey protein supplementation in a healthy teenage athlete population has no negative effect on biomarkers of kidney health. Therefore, researchers should now feel safe conducting whey protein supplementation protocols in a teenage population, utilizing longer intervention periods (i.e. ≥ 8 weeks), with the goal of eliciting positive changes in body composition and athletic performance.

intake. Participants were considered free-living and continued with their individual sport and resistance training programs. Baseline dependent variable differences between groups were compared using independent samples t-tests. Differences in athletic performance measures, body composition, and urinalysis measures were analyzed by a two-way mixed factorial (ANOVA). Significance was set at p ≤ 0.05 and values are presented as mean ± SD. There were no baseline differences (p ≥ 0.05) in age, height, tanner stage, body mass, vertical jump, 5-10-5 pro agility run, squat 1RM, bench press 1RM, PBF, LBM, BMD, or any urinalysis measure. Additionally, no baseline differences (p ≥ 0.05) were observed for mean calorie, carbohydrate, protein, or fat intake. No main effect (p ≥ 0.05) for time was revealed for VJ, 5-10-5 pro agility run, squat 1RM, or any body composition or urinalysis measure, but was revealed for bench press 1RM (p = 0.003). However, there was no group X time interaction was observed for any athletic performance, body composition, or urinalysis variable (p ≥ 0.05). To the best of our knowledge, this study is the first of its kind investigating the effects of whey protein on health and performance in teenage athletes. Results of this study suggest that short-term whey protein supplementation in a healthy teenage athlete population has no negative effect on biomarkers of kidney health. Therefore, researchers should now feel safe conducting whey protein supplementation protocols in a teenage population, utilizing longer intervention periods (i.e. ≥ 8 weeks), with the goal of eliciting positive changes in body composition and athletic performance.
iv ACKNOWLEDGMENTS I would like to acknowledge and express my sincere gratitude to all those who have supported me throughout my graduate career at the University of Rhode Island.
First and most importantly, I would to thank Dr. Disa Hatfield for serving as my major professor, advisor, and mentor. Thank you for agreeing to take me on as a student while in the midst of becoming department chair. Your guidance and expertise in the field have continually inspired me to think critically. I cannot thank you enough for all of your hard work in guiding me in becoming the best researcher I can be. Hopefully this thesis is a testament to that.
Thank you to my committee members, Dr. Jacob Earp and Dr. Kathleen Melanson. To Dr. Earp, thank you for continually allowing me to learn from you and assist in your various research projects throughout my time at URI. Your devotion to research is admirable and something I aspire to. To Dr. Melanson, thank you for being a part of this project. Your reputation in the field of nutrition has preceded you and your enthusiasm for the subject matter is contagious. I am grateful for you for agreeing to serve on the thesis committee of a student you barely know. Lastly, thank you to Dr. Nilton Porto for taking time out of your busy schedule to chair my thesis defense.
I would like to thank all of the Kinesiology faculty at URI for enhancing my graduate experience. I was and still am continually humbled by how warmly I was welcomed to Rhode Island and by how wonderfully I have been treated during my time here. Thank you for making school a place I have enjoyed coming to everyday. I would also like to thank all of my fellow graduate students and graduate assistants that I have interacted with during these past two years. Thank you for taking v this journey with me. In addition, I would like to thank Lisa Vincent for always having a door open to talk and indulge my sometimes bizarre research questions. I would also like to thank Ariana Cambio for assisting in data collection. Your help was sincerely appreciated.
In particular, I would like to thank my fellow graduate assistants Patrick Crowe and Ryan Oakley. Thank you for your friendship these past two years. It has been a pleasure to share the office with you both. We have spent countless hours in and out of the office together and shared many great moments. I cannot wait to see what you two do in the future and I know you will be successful at anything you decide to pursue.
Thank you to AMP Fitness and Andy Procopio for allowing me to conduct this research at your gym and thank you to each individual athlete who volunteered to participate in this study. It was a pleasure to work with all of you.
Lastly, I would like to thank my family, for their love and support. Mom, Dad, and Mark, you have stood by me and supported every decision I have made. I dedicate this thesis to them. ix

INTRODUCTION
In order to set themselves apart from their peers, young athletes are willing to pursue almost anything they believe will give them a competitive advantage (23). This often leads them to replicating not only the training of the professional athletes they admire, but their nutritional and supplementation practices as well (34). Additionally, pressure from peers and the mass media can cause young athletes to turn to illegal, dangerous means of improving performance and physical appearance (12). While research on the use of supplements among adult athletes is well known (13,19), studies on supplement use by teenage athletes are much more limited, with research reporting that between 22.3% to 71% of high school athletes were using some form of supplementation (30).
Common reasons cited for supplement use in youth athletes is similar to that in adults: improvement of athletic performance and recovery from fatigue (48). Many young athletes decide on their supplementation use without advice from others, occasionally seeking help from a parent, trainer, or coach, or in rare circumstances, doctors and dieticians (11,35). One of the most common supplements taken by young athletes is whey protein. Indeed, a study of young elite Japanese athletes participating in the 2010 Youth Olympic Games reported the most popular supplement used was protein powder, with 21.3% of athletes reported using it (38). A survey of elite young UK athletes reported that athletes were taking whey protein with the goal of maintaining strength and increasing their ability to train longer (36). Additionally, usage of protein powders and shakes by adolescents in an effort to improve appearance and strength have been reported (15).
In adults, whey protein has been well documented to be an excellent stimulator of muscle protein synthesis (9), which is essential for increasing muscle mass. Whey protein has also been well documented for its ability to improve muscular strength, athletic performance, and maintain lean body mass and reduce fat mass (32). Research has also reported that diets higher in protein and lower in carbohydrate are most advantageous for promoting weight loss and preserving lean body mass (18,50).
Despite these known benefits, the use of whey protein and/or high protein diets have been criticized for supposedly negatively impacting kidney (16) and bone (4) health. A recent systematic review examining high protein intake (≥ 20% but < 35% of total energy intake) on glomerular filtration rate reported that a high protein intake over a short term period (< 6 months) had no adverse effect on kidney functioning in an adult population (44). In addition, a recent meta-analysis suggested that compared to low or normal protein intakes, a high protein intake (≥1.5 g/kg body weight or ≥20% energy intake or ≥100 g protein/d) does not negatively impact kidney functioning (10). Similar findings have been reported for the effects of protein on bone health, with multiple studies reporting no adverse effects of high protein intake on bone mineral density (BMD) and bone mineral content in a healthy adult population (8,39).
When combined with resistance training, the ergogenic effects of whey protein appear to be enhanced (33). A primary benefit of resistance training is increased muscle strength, and whey protein is often added to resistance training protocols in an effort augment these effects (33). Prior research suggests that the growth spurt observed during puberty is associated with a marked increase in the efficiency of dietary protein utilization for growth (5). Research also suggests that active youth demonstrate greater overall anabolic sensitivity to dietary protein and amino acids than active adults due to their bodies' need to support more rapid increases in lean tissue due to growth and maturation (31). In addition, active youth require more protein per kg of body mass than adults to support growth (31). This suggests that active, postpubertal children are more efficient at utilizing protein and therefore whey protein is a potential ergogenic aid for teenage athletes.
There have been limited studies investigating supplemental protein use in teens, with most investigating its effect on whole body protein balance (46). Given the popularity of whey protein supplementation in teenage athletes and the know benefits it can provide for an adult population, research needs to be done examining how this supplement impacts a teenage population. To the best of our knowledge, there have been no studies done at this point investigating the safety of whey protein in teenage athletes. Therefore, the purpose of this study was to assess the safety of whey protein supplementation in relation to kidney functioning. A secondary purpose was to investigate the short term effectiveness of whey protein supplementation, independent of training, on athletic performance and body composition in teenage athletes.

Experimental Approach to the Problem
A randomized, maturity-matched control group, double-blind study design was used to assess the effects of whey protein supplementation before and after four weeks of continued resistance and sport-specific training. Body composition, athletic performance, and biomarkers of kidney health were assessed one week prior (baseline) to the intervention and again after the final week of the intervention (post). All participants were considered free-living and continued with their normal sport-specific and resistance training programs. Participants and their parents received information about the study and during initial finalization sessions, the methods and procedures of the study were explained, participants and subject's parents were allowed to ask questions, and an in depth medical, training, and nutritional history questionnaire was completed. Each participant signed a child assent form and each parent or legal guardian signed a parental permission form. The Institutional Review Board of the University of Rhode Island approved the research protocol.

Participants
Ten healthy teenage boy and girl athletes across a variety of sports (primarily lacrosse, track and field, and football) from a local gym volunteered to participate in the study. To be eligible to participate in the study, all participants had to be postpubertal (determined via Tanner Stages), have a previously established history of sport participation and resistance training experience (≥ 6 months), and maintain complete training status (without injury) throughout the duration of the study. Detailed medical, nutritional, and training histories were used to assess ability to participate.
Individuals were excluded if they did not meet any of the aforementioned criteria or if they were using any medication that affected exercise capacity, had any cardiopulmonary or metabolic disease, had any orthopedic limitation, or impaired motor development. In addition, individuals were excluded if they identified using any performance enhancing supplements or were currently taking whey protein on a regular basis. Analysis for glucose excretion was defined in a similar fashion, with a negative result being anything >100 mg/dL, and thus 0 mg/dL was used for analysis. Negative ketone excretion was defined as being > 15 mg/dL, and therefore treated as 0 mg/dL for analysis. Nitrite, leukocyte, and blood excretion was defined as either positive or negative, therefore when a negative result occurred, it was reported as 0 for analysis.

Athletic Performance Testing
Measures of athletic performance were assessed at baseline and post.
Performance testing was completed during a single session and supervised by National

Strength and Conditioning Association Certified Strength and Conditioning
Specialists. All participants had a previously established history of sport participation and resistance training experience (≥ 6 months), therefore no familiarization for the athletic performance tests was required as participants were already familiar. Muscular strength was assessed via bench press and squat 1RM following similar guidelines done by Faigenbaum et al. (14). Agility was assessed via 5-10-5 pro-agility run measured via automatic timing (Brower Timing Systems, Draper, UT) and power was assessed via vertical jump measurement (VERTEC, Power Systems, Knoxville, TN).
Both tests were performed three times, and the peak of the three trials was used for analysis. Tests were completed in the following order: vertical jump, 5-10-5 proagility run, squat 1RM, bench press 1RM. All participants completed the same standardized full body warm up prior to all testing. Full rest was given between every trial and every test. Pre and post testing was also performed at the same time of day (± 0.5 hr).

Anthropometrics
Height was measured to the nearest 0.1 cm using a wall-mounted stadiometer (Seca 216, Seca North America, Chino, CA). Participants wore light clothes and no shoes. Measurements were taken from the floor to the top of the head, with feet together on the floor and as close to the wall without touching.

Body Composition Testing
Body composition, including body mass (BM), percent body fat (PBF), and lean body mass (LBM), was assessed at baseline and post via bio-electrical impedance analysis (BIA; InBody 770, InBody, Cerritos, CA) according to manufacturer's guidelines. Each participant was instructed to attend both pre and post testing sessions euhydrated, which was confirmed as a urine specific gravity ≤ 1.020 (21) in order to increase measurement accuracy.
Heel ultrasonography (GE Achilles EXPII ; General Electric Co, USA) was used to measure BMD at baseline and post according to manufacturer's guidelines.
Heel BMD was reported as stiffness index. Stiffness index value, as stated by the manufacturer, is the basic measurement of bone density given by the device. The device utilizes quantitative ultrasound (QUS). QUS is based on the principle that bone, as a porous material, will absorb, scatter and transmit sound wave dependent on stiffness, density and volume of the material (17). Both sound attenuation and the sound velocity are combined to form the stiffness index value.

Dietary Recall
All participants completed a one-day diet log at baseline and post. Participants recorded all food and drink (except water), including brand if possible, method of preparation, and amount. Diet logs were analyzed using Automated Self-Administered 24-Hour (ASA24®) Dietary Assessment Tool (National Institutes of Health, Bethesda, MD) for mean calorie, fat, carbohydrate, and protein intake.

Statistical Analysis
Baseline dependent variable differences between groups were compared using independent samples t-tests. Differences in athletic performance measures, body composition, and urinalysis measures were analyzed by a two-way mixed factorial analysis of variance (ANOVA). Statistical analysis was performed using SPSS (Version 25, Chicago, Ill). Significance was set at p ≤ 0.05. Values are presented as mean ± SD.

Urinalysis
The results indicated that there were no significant (p ≥ 0.05) changes for leukocyte, nitrite, pH, protein, blood, ketone, and glucose content in urine over time.
There were also no main effects revealed for time X group interaction for any urinalysis measure (Table 5).

Athletic Performance Tests
The results indicated that there was no group X time interaction (p ≥ 0.05) for any measure of athletic performance. However, there was a significant (p = 0.003) increase in bench press 1RM over time for both groups ( Table 2).

Body Composition
The results indicated that there were no significant (p ≥ 0.05) changes over time for BM, PBF, LBM, or BMD for the WP or CG. There was no main effect revealed for time and no time X group interaction was observed for any body composition variable (Table 3).

Dietary Recall
The results indicated that there were no significant differences (p ≥ 0.05) at baseline, post, over time, or between groups for any nutritional intake variable (Table   4). However, it is important to note that the post-intervention diet logs were recorded one-day post consumption of the final day of supplement intervention period.
Therefore, the macronutrient data represented at post does not feature the presence of either supplement in both groups.

Kidney Functioning
In the present study, there were no significant changes in biomarkers of kidney functioning for the WP or CG. Thus, whey protein should be considered a safe dietary supplement in teenage athletes given the lack of changes from baseline to post-testing in biomarkers of kidney functioning. This is in agreement with previous research done by Lothian et al. (28). Eleven children (age 12.6 ± 3.6 y) with mild to moderate asthma supplemented with whey protein (18.2 g/d) and researchers monitored changes in serum urea and creatinine. After one month of daily supplementation, there were no significant changes in serum urea or creatinine. While a lower dose than the one given in the present study, the results of this study suggest that an increase in daily protein intake in children has no adverse effect on kidney functioning.

Athletic Performance
In the present study, there were no significant changes observed between groups for vertical jump, 5-10-5 pro agility run, squat 1RM, or bench 1RM.
Additionally, there were no differences observed over time for both groups for vertical jump, 5-10-5 pro agility run, or squat 1RM. However, a significant increase in bench press 1RM was revealed over time for both groups. Thus, the addition of whey protein supplementation to the diet of teenage athletes, administered over a short period of time, resulted in no considerable improvements in common tests of athletic performance.
Previous studies investigating any form of protein supplementation in young athletes with the goal of improving performance and/or muscle mass are scarce.
Laskowski and Antosiewicz (25) randomly assigned twelve young judoists to a 0.5g/kg body mass/day soy protein (mean age 16.8 ± 0.4 y) or an isocaloric control group (mean age 15.6 ± 1.3 y). Participants continued their normal training and after four weeks of supplementation, it was reported that while both groups had significant increases in VO2max and Wingate test performance (peak power output and total work output), increases were significantly higher in the soy protein group than the control group. The dosage and type of protein in this study differs from that of the present study, however. While not done in an exclusively teenage population, Wilborn et al. (49) reported that in combination with eight weeks of structured resistance training, a 24 g whey protein supplement improved vertical jump, broad jump, 5-10-5 pro agility run, and 1 RM bench and leg press testing in a young female population (mean age 20 ± 1.9 y).
Similar results were reported by McAdam et al. (29). Participants (mean age 19 ± 1 y) were randomly assigned to either a whey protein group (77g/d) or an isocaloric carbohydrate control group. After eight weeks of military basic training, the whey protein group performed significantly more push-ups than the carbohydrate control group. An important note to make is that the whey protein dose utilized in this study was significantly higher than that of the present study, but did feature a teenage post-pubertal, although not high school age, population. Antonio et al. (2), however, reported contrasting results. After assigning untrained women (mean age 26.9 ± 1 y) to either an essential amino acid group (average dose of 18.3 g of essential amino acids) or a placebo group and engaging in six weeks of combined aerobic and resistance training, it was reported that while no significant changes in muscular strength were seen, treadmill time to exhaustion increased significantly in the amino acid group. The results of these studies suggest that a longer intervention period (i.e. at least 8 weeks) may be needed to elicit positive changes in athletic performance as a result of whey protein supplementation.

Body Composition
In the present study, there were no significant changes observed between groups for body mass, lean body mass, or percent body fat. Additionally, there were no differences observed over time for both groups for any of the aforementioned variables. Therefore, these results would suggest that supplementing with whey protein over a short term period has no influence, positive or negative, on typical measures of body composition. A longer intervention period is likely needed to observe any kind of change.
Research investigating the effects of whey protein supplementation in youth are limited. Leidy et al. (26) reported that daily consumption of a high protein breakfast (35g/d) over the course of 12 weeks in young adults (mean age 19 ± 1 y) reduced gains in fat mass compared to a control. Additionally, overweight adolescents (age 12-15 y) who consumed 35g/d of skimmed milk, casein, or whey protein for 12 weeks had similar increases in lean mass index, but significantly greater increases in fat mass index and body weight than those who consumed water, despite a similar total caloric intake (3,24).
In a young adult athletic population, results have been more consistently positive. Taylor et al. (41) indicated that after eight weeks of whey protein supplementation (24 g) in female college basketball players (mean age 21 ± 3 y), lean mass significantly increased and fat mass significantly decreased compared to a placebo. Similarly, Candow et al. (7) reported that combined with resistance training, six weeks of whey protein supplementation (1.2 g/kg body mass) resulted in significantly greater gains in lean tissue mass than a placebo in young adults (mean age 24.0 ± 6 y). These results suggest that whey protein supplementation in young adult populations is effective for improving body composition.
No changes were seen in regard to markers of BMD. This is to be expected, as the four week intervention of the present study was too short of a time period to see any changes in BMD, positive or negative, regardless of the supplementation or resistance training. Research in adult populations, however, have reported no negative effects of a prolonged (≥ 1 y) high protein diet or whey protein supplementation on bone health (1,20).
Additionally, no changes in urine pH were seen over time or between groups (Table 5). Urine pH is a measure of the amount of acid in the urine. A normal urine pH value can range from 4.6 to 8.0, with a lower pH being considered more acidic and a higher pH being considered more alkaline (40). A low urine pH could potentially indicate an increased acid load of the body, and to compensate for this, the body may take calcium out the bones in an attempt to neutralize the increase acid (47).
Therefore, a low urine pH could be a sign of reduced BMD. However, no changes in urine pH were seen over time or between groups and urine pH was within the aforementioned normal range at both time points for both groups. This further supports the hypothesis that whey protein supplementation should be considered safe for this population.

Protein Supplementation and Dietary Protein Intake
In the present study, there were no significant changes observed over time or between groups for mean calorie, fat, carbohydrate, and protein intake. Analysis of total dietary protein intake and body weight at pre and post for both groups revealed that at baseline, the WP group was consuming 1.5 g/kg/bw of protein, while the CG was consuming 1.7 g/kg/bw dietary protein. At post, without their respective supplements, the WP was still consuming 1.5 g/kg/bw of protein, while the CG increased slightly to 1.8 g/kg/bw. With the addition of their respective supplements (Table , the WP group was revealed to be consuming 1.7 g/kg/bw at post while the CG was revealed to still be consuming 1.8 g/kg/bw of protein. Current protein recommended dietary allowance (RDA) for healthy adults over the age of 19 is 0.8 g/kg/day (42), while the Acceptable Macronutrient Distribution Range for protein in children (ages 4-18) is 10-30% of total energy intake (20).
However, there appears to no general consensus regarding recommended protein intake for active children and adolescents. Values ranging from 0.6 -2.9 g/kg/day have been proposed (6,37,45).
A recent review by Moore suggests that protein requirements in active children and adolescents are similar to those of athletic adult populations, not only because of the anabolic nature of physical activity, but also because of the need to support the rapid increases in lean body mass that occur in this population (31). Therefore, Moore proposes a daily intake of ~1.6 g/kg/day in this population in order to meet the metabolic demand necessary to sustain a neutral or even positive whole body net protein balance (31). Based on this information, it would appear that the participants in the CG were meeting the proposed necessary protein needs throughout the study (1.7 g/kg/bw pre and 1.8 g/kg/bw post), while those in the WP group were not (1.5 g/kg/bw pre and post). Only with the addition of the supplement (1.7 g/kg/bw) did the WP group meet the proposed protein needs. Therefore, both groups should not be considered high protein, as they were only meeting the proposed protein needs (in the WP group this was only due to the addition of the supplement). Future studies should look to investigate the safety of high protein intake (> 2g/kg/day) in this population.

Conclusion
In summary, daily whey protein supplementation had no adverse effects on kidney functioning or bone health in this population. Furthermore, the results of the present study indicate that whey protein supplementation, at least over a short term period, has no effect, positive or negative, on body composition and typical measures of athletic performance. Further research is needed to investigate if positive changes in body composition and athletic performance can occur over a longer intervention period. To the best of our knowledge, this study is the first of its kind investigating the effects of whey protein on health and performance in teenage athletes.
Despite the fact that the aim of the present study was to examine the effects of a daily addition of whey protein to the diet of teenage athletes while they continued their normal sport specific and resistance training regimen, this could be considered a limitation, as the training of the participants was not controlled. However, participants were matched according to sport, season, and strength and therefore received similar training, mitigating this issue. Future studies could still look to control the training of participants. A strength of the present study was the collection of diet logs at baseline and post.

PRACTICAL APPLICATIONS
In the present study, daily whey protein supplementation over a one month period did not improve body composition or tests of athletic performance in teenage athletes, compared to a carbohydrate placebo. However, no adverse effects on kidney health were revealed as a result of the whey protein supplementation. This data suggests that for an athletic, high school age population, whey protein supplementation is safe over a short period of time. Therefore, future researchers should feel comfortable conducting long term intervention studies, with the main focus investigating the effectiveness of whey protein on performance in this population.   There were no significant differences (p ≥ 0.05) over time or between groups for any measure of body composition. WP = whey protein group, CG = carbohydrate placebo control group. There were no significant differences (p ≥ 0.05) over time or between groups for any nutritional intake variable. WP = whey protein group, CG = carbohydrate placebo control group, CHO = total dietary carbohydrate intake, PRO = total protein intake. There were no significant differences (p ≥ 0.05) over time or between groups for any nutritional intake variable with the addition of their respective supplement. WP = whey protein group, CG = carbohydrate placebo control group, CHO = total dietary carbohydrate intake, PRO = total protein intake.

Abstract
The pursuit of excellence in athletic performance is not solely an adult interest.
Long-term athletic development models start as early as age five in some sports (Lloyd et al., 2016). In addition to the physical aspects of training, young athletes are also mirroring the nutritional and supplementation practices of adult athletes (Naylor & Cherubini, 2008). Major supplement companies are already ahead of the curve in terms of marketing, having nutritional supplementation products specifically marketed towards young athletes with claims of improved performance. While research on the use of supplements among adult athletes is well known (Erdman et al., 2006;S.-H. S. Huang et al., 2006), few studies on supplement use by teenage athletes have been done. Research has been reported that between 22.3% to 71% of high school athletes were using some form of supplementation (McDowall, 2007). Whey protein is a common and popular supplement taken by adults and young athletes. However, knowledge regarding its safety and efficacy in youth athletes is currently insufficient.
Common reasons cited for supplement use in youth athletes is similar to that in adults: improvement of athletic performance and recovery from fatigue (Wiens, Erdman, Stadnyk, & Parnell, 2014). While the benefits (Devries & Phillips, 2015;Maughan et al., 2018) and safety (Campbell et al., 2007) of whey protein supplementation in adults is undisputed, the safety nor the performance enhancing benefits of whey protein supplementation in youth athletes has been investigated. This study will seek to better understand the effects of this supplement on the health and athletic performance of young athletes ages 13-18.

Introduction
Whey protein is one of several primary proteins found in cow's milk. Whey protein is typically defined as a mixture of proteins isolated from whey, which is the liquid remaining after cow's milk has been curdled and strained. Whey is a by-product of the cheese and curdle manufacturing process and was previously considered a waste product. However, whey was found to have several health applications, and was no longer considered a by-product of the cheese manufacturing process. Instead, it became viewed as a co-product (Marshall, 2004), with importance placed on its production. The commercial success of whey protein has led to the development of high quality whey protein supplements by manufacturers. Whey protein contains all of the essential amino acids the body requires (Walzem, Dillard, & German, 2002).
Whey protein, in its powered form, is an incredibly popular dietary supplement and is purported to have immunoenhancing effects as well as positive benefits on exercise performance and body composition.
Whey protein is typically taken with intent to improve athletic performance and to recover from fatigue in adults (D. P. J. Cribb, 2005). Common reasons cited for supplement use in youth athletes is similar to that in adults: improvement of athletic performance and recovery from fatigue (Wiens et al., 2014). Teenage athletes are being increasingly exposed to an expanding market of nutritional supplements and tend to be heavily influenced by professional athletes, as well as their own peers, when regarding supplementation use. Many young athletes decide on their supplementation use without advice from others, occasionally seeking help from a parent, trainer, or coach, or in rare circumstances, doctors and dieticians (Diehl et al., 2012;Petróczi et al., 2007). Researchers have reported that young athletes are taking supplements with the goals of staying healthy, increasing energy, and improving immune function (Wiens et al., 2014).
Few studies on supplement use by teenage athletes have been done. Several different studies have reported that between 22.3% to 71% of high school athletes were using some form of supplementation (McDowall, 2007). Among a high school cohort of 270 athletes, 58% had used some form of supplementation (Kayton, Cullen, Memken, & Rutter, 2002). A study of young elite Japanese athletes participating in the 2010 Youth Olympic Games reported the most popular supplement used was protein powder, with 21.3% of athletes reported using it (Sato et al., 2012). A survey of elite young UK athletes reported that athletes were taking whey protein with the goal of maintaining strength and increasing their ability to train longer (Petróczi et al., 2008).
Another survey study, this time in young, non-elite Canadian athletes, reported that protein supplements were the most popular supplement choice, despite an already high dietary intake of protein (Parnell, Wiens, & Erdman, 2016). This study helps to further establish the popularity of protein supplementation in youth athletes, in this case in a non-elite population.
Prior research has suggested that resistance training resulted in a downregulation in protein metabolism in healthy children (Rodriguez, 2005). This highlights a potential need for greater protein intake in pre-pubescent children participating in a resistance training program to avoid that downregulation in protein metabolism. However, after puberty, there is research suggesting that the growth spurt observed during puberty is associated with a marked increase in the efficiency of dietary protein utilization for growth . The results of this study suggest that post-pubertal children are more efficient at utilizing protein and therefore whey protein can be a potentially safe ergogenic aid for teenage athletes.
No research has been done investigating the effects of whey protein on kidney function in an under-18 population. Research on adults has been extensive, however.
Contrary to popular belief, it has been well documented that a high protein diet (considered to be protein intake greater than the recommended daily amount) does not have any adverse effects on kidney function in healthy adults (Martin, Armstrong, & Rodriguez, 2005).
While there has been no direct research investigating the effect of whey protein supplementation on body composition and athletic performance in an under-18 population, the positive effects on an adult population have been well documented.
Compared to a control, whey protein supplementation combined with resistance training, can help preserve fat free mass, increase lean body mass, and decrease body weight and body fat (Miller, Alexander, & Perez, 2014b). Similarly, it has been well established that whey protein supplementation can improve athletic performance and muscle strength compared to a control (Hayes & Cribb, 2008;Pasiakos, McLellan, & Lieberman, 2015).
A combination of a proper diet and resistance training has been suggested to increase mineral density in youth (Faigenbaum et al., 2009). Research investigating the effect of whey protein on bone health in humans in has been scarce, with the majority of research focusing on rats, and none being done in an under-18 population.
This research on rats has been positive however, showing that whey protein had the ability to increase femoral bone strength (Kato et al., 2000;Kim, Kim, Kim, Imm, & Whang, 2015;Takada et al., 1997). Similar research that has been done in humans has focused on using milk basic protein (MBP), a component of whey protein, to improve bone health. MBP has been suggested to stimulate proliferation and differentiation of osteoblastic cells as well as suppress bone resorption (Takada, Aoe, & Kumegawa, 1996). Studies utilizing daily MBP supplementation for six months have revealed a positive effect on bone mineral density in comparison to a placebo (Aoe et al., 2001;Yamamura et al., 2002).
While the benefits of whey protein supplementation in adults is well documented (Morton et al., 2018), the safety nor the performance enhancing benefits of whey protein supplementation in youth athletes has been investigated. Based on the aforementioned research, it was deemed pertinent that the safety and efficacy of whey protein in teenage athletes be investigated. Thus, the purpose of this study was to investigate the effects of whey protein supplementation on athletic performance, body composition, and biomarkers of bone and kidney health in teenage athletes.  (McDowall, 2007). While health and illness prevention were cited as the main reasons for taking supplements, enhanced athletic performance was also reported as a strong motivating factor among young athletes.

Supplement Use Amongst Teenage Athletes and Reasons For
The review also suggests that females use supplements more frequently than males and their reasons were for improved health and recovery, as well as replacing an inadequate diet.  (Parnell et al., 2016).
One-hundred and eighty-seven (84 male, 103 female) athletes were recruited from sporting communities and local public schools. Ages ranged from 11 to 18 years.
Analysis by age groups of 11-13 years and 14-18 years reported an increased use of protein powder in the older age group with regular use at 18%, occasional at 45%, and never at 37% vs. 10% regular, 23% occasional, and 68% never in 11-13 years (p = 0.001). Protein supplements were most popular in this cohort; despite an already high dietary intake of protein. This study helps to further establish the popularity of protein supplementation in youth athletes, in this case in a non-elite population. This also establishes supplement use in a younger, potentially prepubescent, population (i.e. 11-13 years).
Research investigating the nutritional supplementation practices in elite UK junior national track and field athletes has also been performed (Nieper, 2005). Survey data was taken from 32 athletes (20 males, 12 females, mean age = 18 y) to assess the prevalence and type of supplement used, the reasons for use, knowledge of supplements, and sources of information. Results reported that 62% of athletes took at least one supplement regularly. Additionally, supplement use was higher in females (75%), than males (55%), although the relationship was not significant (p = 0.45).
Reasons cited for using supplements were for health (45%), to enhance the immune system (40%), and to improve performance (25%). This helps to further establish the reasons behind supplement use in teenage athletes. This study was limited however by its small sample size and lack of identification of specific supplements.
Teenage athletes in the UK were again examined, this time by Petróczi et al.
The purpose of this survey study was to investigate nutritional supplement use by elite young UK athletes, and to establish whether a rationale versus practice incongruence exists, and to investigate the sources of information (Petróczi et al., 2007 (Braun et al., 2009). One-hundred sixty-four elite young athletes across various sports completed a survey that assessed supplement use during the previous four weeks. These surveys showed that 80% of athletes reported using at least one supplement, with no significant differences between types of sports (p = 0.53). Vitamins (76%) and minerals (87%) were the most popular, followed by sport beverages (69%), carbohydrate supplements (64%), and protein/amino acid products (30%). The use of protein products was greater in males than in females (42% v. 20%), however the relationship was not significant (p = 0.07). Among athletes who used or had used supplements, 63% stated that they did so for "maintenance of health", while 44% stated they did so for "improvement of immune functions." Athletes who cited performance-related reasons had been using significantly more protein (p < 0.001) and carbohydrate (p < 0.05) products. This study indicates that while protein supplementation may not be the most common nutritional supplement taken, it is for athletes believing it will improve performance.
Duellman et al. sought to determine whether male high school football players, who choose to take protein supplements, have more misconceptions regarding their effectiveness than those who did not (Duellman, Lukaszuk, Prawitz, & Brandenburg, 2008). Sixty-one male high school football players were recruited for the study.
Thirty-nine identified as users of protein supplements. Thirty-two of those users identified gaining muscle as the main reason for taking protein supplements. The results also indicated that protein supplement users had greater levels of misconceptions about protein supplementation than the non-protein users. The results of this study further indicate the need for continued research into this topic with a primary goal being able to provide youth athletes proper education about correct supplement usage.

Muscle Strength and Athletic Performance
Protein supplements are frequently consumed by athletes and recreationally active adults of all ages with the goal of improving muscle strength and mass and therefore subsequent performance. Research has suggested that both pre and post exercise ingestion of whey protein can increase muscle protein synthesis, resulting in a positive net protein balance, which is important for muscle hypertrophy (Hulmi, Lockwood, & Stout, 2010). The use of protein supplements have also been documented as a potential treatment for sarcopenia (Nabuco et al., 2018), which is the loss of skeletal muscle mass as one ages. However, the breadth of this section of the review will focus on the effects of protein supplementation, specifically whey protein when possible, on measures of athletic performance and muscle strength in healthy young-to-middle-aged adults.
In order to assess its effectiveness on muscle strength, whey protein is often combined with resistance training, or given to resistance trained individuals (Naclerio & Larumbe-Zabala, 2016). A primary benefit of resistance training is increased muscle strength, and whey protein is often added to resistance training protocols in an effort augment these effects.
Investigating this idea, Burke et al. conducted one of the first studies examining the effects of whey protein supplementation combined with resistance training on muscle strength (Burke et al., 2001). Twenty-seven participants (18 female, 9 male) who were not participating in resistance type training participated in the study. Participants were randomly and equally placed into either a whey protein, soy protein, or a placebo group. Knee extension and flexion peak torque, and bench press and squat strength were used to assess muscle strength. Whey protein dosage was 1.2 g/kg body mass/day while the placebo was 1.2 g/kg body mass/day of maltodextrin. All participants followed the same resistance training protocol for 12 weeks. Only knee extension peak torque was reported to have increased significantly in the whey protein group compared to the placebo group. There were no differences revealed for knee flexion peak torque, squat and bench press strength between the groups. Participants only supplemented for the first six weeks of the study, and not the final six weeks. This almost certainly affected any potential gains in strength made as a result of the whey protein. This study is noteworthy however in that provides some rationale for whey protein supplementation and allows for continued investigation.

Following Burke's lead, Coburn et al. utilized a randomized double-blind
design to compare whey protein and a placebo, combined with resistance training, on muscle strength (Coburn et al., 2006). Thirty-three men (mean age 22.4 ± 2.4 y) were divided into three groups: a supplement group (n = 11), a carbohydrate placebo group (n = 12), and a no supplement control group (n = 10). The supplement contained 20 g of whey protein and 6.2 g of leucine. Participants participated in a unilateral dynamic constant resistance leg extension exercise protocol three times per week for eight weeks. Supplements were consumed 30 minutes prior to and immediately after each exercise session. One repetition max testing on a unilateral leg extension machine was performed at weeks 0 and 8. The whey protein group's 1RM strength increased significantly (p ≤ 0.05) at the end of the eight weeks compared to both the placebo and the control group. This study shows that in combination with resistance training, whey protein supplementation can increase strength gains compared to a carbohydrate placebo. However, this study did not assess dietary protein intake at any point. This leads to the possibility that the whey protein supplement may have been distributed to a group of people that were protein deficient compared to the placebo group.
Willoughby and colleagues also investigated the effects of whey protein supplementation on muscle strength over the course of 10 weeks (Willoughby, Stout, & Wilborn, 2007). Nineteen untrained males were randomly assigned to either a 40 g/d whey protein group (n = 9), or a 40 g/d dextrose group (n = 10). All participants engaged in the same resistance training protocol four times per week. Strength was assessed via bench press and leg press 1RM. At the end of 10 weeks, the whey protein group had significantly higher (p ≤ 0.05) increases in bench press and leg press 1RM than the dextrose group. A strength of this study was that macronutrient intake within each group and between the two groups did not change significantly over the course of the 10 weeks, and that both groups engaged in the same resistance training protocol, the observed improvements in muscle strength in the protein group are most likely due to the ingestion of the protein supplement. This study aids in establishing whey protein as an effective ergogenic aid.
Walker et al. also reported similar results, this time without a structured resistance training intervention (Walker et al., 2010). Thirty moderately trained male participants (mean age 26.9 y) were separated into either a combined 19.7 g whey protein and 6.2 g leucine group (n = 18) or an isocaloric placebo group (n = 12).
Participants engaged in at least three days of total body training per week. After eight weeks of daily supplementation, participants in the whey protein group had significant increases in 1RM bench press and one-minute push-up test compared to week one, while the placebo group did not see any significant changes. Neither the supplement nor the placebo saw any improvements in other non-traditional measures of athletic  (Joy et al., 2013). Twenty-four resistance trained males (mean age 21.3 ± 1.9 y) were randomly divided into either a 48 g whey group (n = 12) or a 48 g rice group (n = 12). All participants engaged in the same resistance training protocol three times per week for eight weeks and consumed their given supplement after each training session. Bench press and leg press 1RM were used to assess strength. Unlike prior research, whey protein supplementation did not present an advantage over its comparison. While both groups saw increases in strength at the end of the eight weeks, there was no difference between groups. These results suggest that differences in protein composition appear to be less relevant when consumed in high doses.
While most research typically focuses on a male population, Wilborn et al.
chose to examine the effects of whey versus casein protein in female athletes (Wilborn et al., 2013b). Sixteen female basketball players (mean age 20 ± 1.9 y) were randomly divided into a 24 g whey (n = 8) or 24 g casein group (n = 8). All participants participated in the same supervised four-day per week resistance training program for eight weeks. Supplements were consumed 30 minutes prior to and immediately after training. At weeks zero and eight, participants underwent vertical jump, broad jump, 5-10-5 agility, and 1RM bench press and leg press testing. After eight weeks, there were no differences seen between groups for any of the aforementioned measures. All measures did increase, however. While this study shows no performance advantage between whey and casein, it does show positive benefits for protein supplementation in a female population.
Positive effects of whey protein supplementation on muscle strength have been seen in some, but not all cases. In some untrained populations, research has documented no differences in measures of muscle strength between whey and a placebo after engaging in a structured resistance training protocol for eight weeks (Herda et al., 2013;Mielke et al., 2009;Weisgarber, Candow, & Vogt, 2012).
Furthermore, it has also been reported that a combination supplement of whey protein, creatine, and carbohydrates has no advantages over a carbohydrate-only supplementation when consumed post-exercise in relation to muscle strength, endurance, and anaerobic cycling performance (Chromiak et al., 2004). This suggests that whey protein supplementation has more efficacy in a trained population.
While not as established in the literature as research on the effects of whey protein in resistance trained population and/or on strength measures typically associated with resistance training, there is a growing body of research investigating the effects of whey protein on aerobic and endurance sport performance. This research, however, has been mixed at best. Acute whey protein supplementation has been suggested in some instances to have a negative effect on cycling time trial performance (Macdermid & Stannard, 2006;Schroer, Saunders, Baur, Womack, & Luden, 2014), while in others it has reported no negative effect (Oosthuyse, Carstens, & Millen, 2015). Time to exhaustion treadmill runs have been reported to significantly improve after 6 weeks of amino acid supplementation in an untrained population (Antonio, Ellerbroek, & Carson, 2018). Additionally, in elite endurance athletes, whey protein has been reported to improve performance and markers of recovery (Hansen, Bangsbo, Jensen, Bibby, & Madsen, 2015;W.-C. Huang et al., 2017).

Body Composition
In addition to being taken for its positive effects on muscle strength, whey protein is often taken as a weight loss/maintenance aid. Similar to its effects on muscle strength and athletic performance, the use of whey protein, combined with or without resistance training, has been documented to improve several parameters of body composition, including lean body mass and body fat (Miller et al., 2014). Research has suggested that diets higher in protein and lower in carbohydrate are most advantageous for promoting weight loss and preserving lean body mass (Hession et al., 2009;Wycherley et al., 2012). Whey protein has also been documented to increase satiety and suppress appetite more than other proteins (Anderson, Tecimer, Shah, & Zafar, 2004;Hall, Millward, Long, & Morgan, 2003). In addition, whey protein has been suggested to be superior to other protein sources for increasing and supporting muscle protein synthesis (Devries & Phillips, 2015;Phillips, Tang, & Moore, 2009 All participants engaged in the same nine month whole body resistance training program. Body composition, measured via DXA, was assessed at three, six, and nine months. While body mass and lean body mass increased significantly at three months and remained higher at six and nine months in all groups, lean body mass was significantly greater at all time points in the whey protein group compared to the other two groups. While body mass and body fat percentage decreased significantly across all time points, no differences were seen between groups. These results suggest that daily whey protein supplementation, in particular over a long period of time, can promote significant increases in lean body mass. Similar results were also reported by Cribb and colleagues (P. J. Cribb et al., 2006). Comparing 90g/d of whey protein to 90g/d of casein over the course of 10 weeks, it was revealed that the group supplementing with whey protein had significantly (p < 0.01) greater gains in lean mass (5.0 ± 0.3 kg) and significantly (p < 0.05) greater losses in fat mass (-1.5 ± 0.5 kg) compared to the casein group. All participants engaged in the same resistance training protocol. This suggests that the amount of whey protein consumed is important, with higher amounts being perhaps more beneficial for reducing fat mass and increasing lean mass.
Similar to testing its effects on muscle strength, whey protein is often combined other supplements in attempts to augment its effectiveness. In this vein, Hulmi et al. compared the effects of whey protein with or without added carbohydrates on body composition (Hulmi et al., 2015). Eighty-six active male participants were divided into three groups: a 30 g whey protein group (n = 22), a 34.5 g isocaloric maltodextrin group (n=21), and a combination 30 g whey protein and 34.5 g of maltodextrin group (n = 25). Participants also engaged in a structured resistance training protocol two to three times per week for 12 weeks and consumed their given supplement post training and on training days only. Body composition was assessed via DXA. While all groups showed increases (p ≤ 0.05) in fat-free mass, the whey protein group had a larger relative increase (per kg of bodyweight) in fat-free mass than both the carbohydrate only group and the combined group. Total fat mass also saw a significant decrease after 12 weeks in both the whey protein only and combination groups, but not the carbohydrate only group. This study suggests that if one is aiming to reduce fat mass, consuming whey protein after exercise provides an advantage over carbohydrate supplementation.
While most research focuses on a male resistance trained population, Taylor et al. examined whey protein supplementation in female basketball players (Taylor, Wilborn, Roberts, White, & Dugan, 2016). Fourteen healthy Division III female basketball were randomly and assigned to 24g whey protein group (n = 8, mean age 20 ± 2 y) or a 24 g placebo group (n = 6, mean age 21 ± 3 y) for eight weeks. Body While most studies combine whey protein supplementation with resistance training, Frestedt and colleagues chose to simply add whey protein to the diet of their participants, with no resistance training intervention (Frestedt, Zenk, Kuskowski, Ward, & Bastian, 2008). One-hundred and six participants were randomly assigned to a twice daily 10g whey protein group or an isocaloric maltodextrin control group.
Participants were divided into a 42 g protein group (n = 11, mean age 20.3 ± 1.6 y) and an isocaloric placebo group (n = 10, mean age 21.0 ± 1.2 y) and engaged in a fourday per week, split resistance training routine. Participants consumed their given supplement twice daily: once in the morning and again post training. Body composition was assessed via DXA at 0, 6, and 12 weeks. While no significant changes in body mass, lean body mass or percent body fat were observed in either group from 0 to 12 weeks, lean body mass did increase by 1.4 kg in the protein group compared to only 0.1 kg increase in the placebo group. This was only a trend, and no significance was seen. This may be explained by the relatively low caloric intake seen by the participants as consuming insufficient calories may compromise the body's ability to increase its lean mass.

Protein Intake and Kidney Function
Diets high in protein have been previously rumored to have a negative effects on kidney functioning. This idea has received particular attention recently, with the increase in popularity of diets that feature high protein intakes, such as the paleo, ketogenic, and Atkins diet. The concern being that the primary job of the kidneys is to filter waste from the bloodstream, and that excess protein increases the rate at which this occurs. This increased rate, also known as glomerular hyperfiltration, may cause damage to the kidneys, and thus cause waste products to build up in the body (Kalantar-Zadeh & Fouque, 2017). There is experimental data in animal models showing that long-term dietary protein intake exceeding 1.5g/kg of body weight per day may cause glomerular hyperfiltration (Hostetter, Meyer, Rennke, & Brenner, 1986). Most kidney issues caused by increased protein intake in humans have occurred in individuals either at risk for chronic kidney disease or already have known kidney disease, and similar claims in humans free of kidney issues have gone unsupported (Friedman, 2004). A similar systematic review and meta-analysis also investigating high protein intake on kidney function was conducted by Devries et al. (Devries et al., 2018).
However, they sought to compare high protein intakes with normal or low protein intakes. A high protein intake was defined as either ≥ 1.5 g/kg body weight, ≥ 20% of total energy intake, or ≥ 100g/day, while normal/low protein intake was defined as ≥ 5% less total energy intake from protein per day as compared to the high protein intake. A total of 28 studies were analyzed, and all of the studies were RCTs. Total participant count was 1,358, with studies raging from six to 307 participants. Changes in GFR were again utilized to assess kidney function, and analyses were conducted using postintervention GFR and the change in GFR from pre to post. Changes in GFR pre/post intervention period did not differ (p = 0.16) between protein intakes.
However, a small increase in GFR was observed after in high protein intakes (p = 0.002), and a linear relationship was observed between protein intake and GFR in the post-only comparison (r = 0.332, p = 0.03), but not between protein intake and the change in GFR (r = 0.184, p = 0.33). The results of this research continue to support the notion that high protein intakes do not adversely affect kidney function in healthy adults. Additionally, it suggests that low protein intake does not necessarily protect against increases in GFR and kidney health.

Protein and Bone Health
Similar to the misconceptions about protein and kidney health, it has also been speculated that a high protein intake can reduce calcium in bones, potentially causing osteoporosis. This theory is based on the idea that a high protein intake increases the acid load of the body, and to compensate for this, the body takes calcium out of bones to neutralize this increased acid (Barzel & Massey, 1998). However, in order to maintain bone structure, particularly as one ages, there is a certain amino acid requirement from dietary protein needed (Wallace & Frankenfeld, 2017), creating something of a paradox. Therefore, it is important to investigate these claims to determine the true relationship between protein and bone health.
Darling et al. conducted the first systematic review and meta-analysis regarding this topic in 2009 (Darling, Millward, Torgerson, Hewitt, & Lanham-New, 2009). Thirty-one cross-sectional surveys examining bone mineral density (BMD), bone mineral content (BMC), and bone markers were included in the systematic review. BMD was assessed at various sites, including the lumbar spine, calcaneus, femoral neck, femur, hip, and radius. Little evidence was suggested of a negative relationship between protein intake and BMD. Fifteen cross sectional surveys reported a significant positive relationship between protein intake and BMD at least one site.
However, 18 studies reported no significant correlation between protein intake and at least one BMD site. No studies showed a significant increase in BMD loss with increased protein intake, and it was revealed that protein intake was not a significant predictor of BMD. Similar results were revealed for bone markers, as the crosssectional surveys showed little evidence that protein intake had any influence. Results were more mixed for BMC, as four cross sectional surveys reported a positive correlation between protein intake and BMC for at least one site, while two reported no significant correlation, and only one survey reported a significant negative correlation between protein intake and BMC. Overall, the results of this systematic review and meta-analysis show that while there may be a small benefit of protein intake on bone health, there is at least no detrimental effect. There was evidence from five RCTs that higher protein intake may actually have a protective effect on lumbar spine BMD compared with lower protein intake (95% CI: 0.06%, 0.97%). However, no effect was reported for total hip, femoral neck, or total body BMD. Overall, there was no evidence of adverse effects of higher protein intake on BMD.
In an attempt to examine the relationship between protein intake and bone health for an extended period, Antonio et al. investigated the effect of a high-protein diet on BMD in exercise trained women over a one year period (Antonio et al., 2018).
A high protein diet was defined as > 2.2 g/kg/day. BMD was assessed via dual-energy DXA. Twenty seven female participants (mean age = 37 y) participated in the study.
Participants engaged in a minimum of resistance and/or aerobic training three times per week. No changes (p > 0.05) were reported over the course of the study for BMC, BMD, and lumbar spine BMC and BMD. These results suggest that a high protein diet has no adverse effects on BMD over a long term period.
While all of the aforementioned research has simply investigated a highprotein intake, it is important to investigate the specific effects that whey protein supplementation has on bone health. Kerstetter et al. attempted to do this by examining the effects of whey protein supplementation in older Caucasian adults (Kerstetter et al., 2015). A randomized, double-blind, placebo-controlled study design was utilized. Two-hundred and eight men and women were separated into two groups: a 45 g/d whey protein group (mean age = 69.9 ± 6.1 y) and an isocaloric carbohydrate control group (mean age = 70.5 ± 6.4 y). Participants consumed their given supplement daily for 18 months and BMD and body composition was assessed via DXA at baseline, nine and 18 months. No significant differences (p ≥ 0.05) were reported between groups for lumbar spine, total femur, and femoral neck BMD. Total lean mass (p = 0.011) and truncal lean mass (p = 0.003) were significantly lower in the carbohydrate group compared to baseline, while lean mass in the protein group was unchanged from baseline. While not significant, total lean mass (p = 0.069) was higher in the protein group at 18 months. Lean truck mass was significantly (p = 0.048) higher in the protein group at 18 months. Total fat mass also significantly (p = 0.018) increased over the 18 months in the carbohydrate group. A similar change was not seen in the protein group. The results of this study suggest that whey protein supplementation can promote positive changes in body composition without adversely affecting skeletal health. While whey protein supplementation did not negatively impact bone health, it did not positively impact it either.
The results of the pervious study were also in agreement with those reported by Zhu et al. several years prior. They also utilized randomized, double-blind, placebo controlled study (Zhu et al., 2011). Two-hundred and ninety healthy postmenopausal women were separated into two groups: a 30 g/d whey protein group (mean age = 74.2 ± 2.8 y) and a 2.1 g/d protein placebo group (mean age = 74.3 ± 2.6 y) and tracked for two years. BMD was assessed via DXA at baseline and at one and two years. While there was a significant decrease in hip DXA over the two years, there was no difference between groups. These results further demonstrate that while whey protein supplementation has no adverse effect on bone, it was also not beneficial for bone health.
Similarly, Wright et al. also reported no benefits of whey protein supplementation on bone health (Wright, McMorrow, Weinheimer-Haus, & Campbell, 2017). Unlike the previous studies that investigated healthy older populations, this study looked at middle age overweight and obese adults. Again, a double blind, randomized, placebo-controlled study design was used. Participants (n = 186, 108 females, 78 males, mean age = 49 ± 8 y, BMI: 30.1 ± 2.8 kg/m 2 ) consumed either a 0, 20, 40, or 60 g/d whey protein supplement daily for 36 weeks. Participants also took part in a resistance training program twice per week and an aerobic training program one day per week. BMD and BMC were assessed via DXA. There were no differences seen for any whey protein dose and BMD and BMC after the 36 weeks. These results further support the notion that whey protein supplementation has no positive or negative impact on bone health, in this case in an overweight and obese middle age population.

Conclusion
While mixed at times, a significant body of evidence has readily exhibited a number of positive benefits that whey protein supplementation can have on muscle strength, athletic performance, and body composition. These benefits extend from young healthy adult populations to elderly populations with sarcopenia and have been documented to occur in as little as 8 weeks. Furthermore, whey protein has been reported to be more effective than other protein sources at improving these measures and has been reported to be effective with or without the addition of a structured training program.
Additionally, considering the lack of side effects that high protein intakes have on bone and kidney health, concerns for supplementing with whey protein in an under-18 population should be lessened. Based on the current literature, whey protein presents itself as a popular supplement in a teenage athlete population and appears to be growing in popularity. Therefore, based on the knowledge that whey protein is popular amongst teenage athletes and has been well documented to be an effective ergogenic aid in young adult populations, it would appear beneficial to investigate the effectiveness of whey protein supplementation in an under-18 population. Since little to no research of this nature has been done, future research should investigate these ideas across a wide variety of populations, both pre and post pubertal, and for intervention periods of at least eight weeks in length.