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Some scientists and professional organisations have called for an increase in dietary protein for those who reach a threshold level of exercise, i.e. endurance athletes. But there are individual scientists who question this recommendation. Limitations in the procedures used to justify changing the recommended daily allowance (RDA) are at issue. N balance has been used to justify this increase; but it is limiting even when measured in a well-controlled clinical research centre. Experimental shortcomings are only exacerbated when performed in a sports or exercise field setting. Another laboratory method used to justify this increase, the isotope infusion procedure, has methodological problems as well. Stable isotope infusion data collected during and after exercise cannot account for fed-state gains that counterbalance those exercise losses over a 24 h dietary period. The present review concludes that an adaptive metabolic demand model may be needed to accurately study the protein health of the active individual.