Author

Jennifer Arts

Date of Award

2009

Degree Type

Thesis

Degree Name

Master of Science in Nutrition and Food Science

Department

Nutrition and Food Sciences

First Advisor

Kathleen J. Melanson

Abstract

Problem Statement: Obesity and its related metabolic disorders rank among the leading causes of illness and mortality worldwide. The prevalence of obesity has led researchers to focus on body weight regulation and the balance between energy intake and energy expenditure.

Background: Studies have suggested that ghrelin is involved in both short and long term energy balance. Previous research has examined the relationships among BMI, ghrelin and appetite but few studies have investigated the role that fitness status plays in relation to these.

Methods: Data from two studies that were previously conducted in the Energy Metabolism Laboratory were combined for a secondary data analysis. One hundred nine subjects (87 females, 22 males; 19.4 ± 2.1 years; BMI 22.9 ± 3.9 kg/m2) were included in the analysis. Cardiorespiratory fitness (V02max) was estimated by the Queen's College Step test and self-reported physical activity was determined by the International Physical ~ctivity Questionnaire. Ratings of appetite (by 1 OOmm visual analog scales), plasma total ghrelin (by RIA) and insulin (by ELISA) were analyzed following a 1 Oh fast and 30min after a standardized meal.

Results: Ghrelin was significantly correlated with BMI in both the fasting (r=-0.290, p=0.005) and fed (r=-0.381, p=0.001) states. Significant negative correlations were also found between V02max and both fasting ghrelin (r=-0.305, p=0.003) and fed ghrelin (r=-0.336, p=0.005). Fasting ghrelin was also significantly correlated with vigorous physical activity (r=-0.242, p=0.019), waist circumference (r=-0.298, p=0.004) and insulin (r=-0.324, p=0.012). Ghrelin and appetite were not significantly related at single time point measures (t=O, 30 min). BMI was positively correlated with dietary restraint (r=0.258, p=0.007) and disinhibition (r=0.276, p=0.004), whereas V02max was negatively correlated with dietary restraint (r=-0.350, p<0.001). ANOV A indicated that subjects with BMis above the median had significantly lower fasting ghrelin (692.2±237.9 pg/mL vs. 802.2±266.0 pg/mL, p=0.037) and fed ghrelin (575.0±164.4 pg/mL vs. 710.2±226.4 pg/mL, p=0.005) and significantly greater disinhibition (6.5±3.1 vs. 4.8±3.1, p=0.005) compared to those with BMis below the median. Subjects with a higher fitness status reported significantly lower fasting satiety (31.4±22.3 vs. 36.8±22.2, p=0.022), greater desire to eat (53.3±17.5 vs. 45 .5±20.5, p=0.037), and less dietary restraint (7.8±5.2 vs. 11.3±5.4, p=0.001) compared to subjects with a lower fitness status.

Significance and Conclusions: These findings confirm previous relationships reported between BMI and ghrelin, subjective appetite and eating behaviors and corroborate lack of associations between single-point time measures of ghrelin and appetite. Additionally, results indicate that cardiorespiratory fitness may be related to circulating ghrelin levels, subjective appetite, and degree of dietary restraint. Further study is needed to determine the nature of these relationships.

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