Energy and Macronutrient Metabolism
Objectives : The progressive loss of muscle mass, or sarcopenia, is inherent to aging and related to functionality and independence. It is well established that the loss of muscle mass can be mitigated with adequate dietary protein intake. To help the consumers meet protein requirements utilizing a variety of protein food sources, the Dietary Guidelines for Americans (DGAs) published an “ounce equivalents” recommendation for protein food sources. However, the actual equivalency of these varied protein food groups has not been established. We examined the responses of protein kinetics in response to consumption of ounce equivalents of ground beef, sirloin, eggs, pork loin, kidney beans, peanut butter, tofu, and mixed nuts in young subjects.
Methods : Subjects adhered to 3 days of activity and dietary control, and were then studied using an 8.5 h metabolic study which included a 4.5 h basal overnight-fasted period followed by a 4 h post-meal period. All groups were balanced by sex (4 males/4 females).
Results : Consumption of animal-based protein food sources resulted in higher whole body net balance than the plant-based protein food sources (P < 0.05). Consumption of beef sirloin, eggs, and pork loin induced a higher whole-body anabolic response than ground beef and the plant- based proteins. Consumption of tofu (soy-protein) induced a higher whole-body anabolic response than the other plant proteins (P < 0.05). The improvement in whole-body net balance with animal-based protein sources and tofu was due to a significant increase in protein synthesis (P < 0.05) as well as a significant suppression of protein breakdown in most protein sources (P < 0.05). Whole-body net balance was related to higher plasma EAA concentrations with animal-based protein sources and tofu realizing greater peripheral concentrations (P < 0.05).
Conclusions : The results of this study indicate that the “ounce equivalents” as expressed in the DGAs do not produce equivalent anabolic responses, nor are they equivalent in terms of the amount of protein provided, or the caloric cost of protein consumption. The magnitude of anabolic response appears to be largely determined by the amount of essential amino acids per gram of protein food source.
Funding Sources : The Beef Checkoff, National Pork Board, and Egg Nutrition Center