Manipulating dietary protein density and its effect on training-induced muscle performance and overall health among middle-aged adults

By 2050, the aging population worldwide is expected to increase vastly. This has major implications as the progressive loss of muscle strength is a common consequence of aging and negatively impacts physical performance and ultimately, independence and quality of life. The underlying mechanistic cause of this age-related strength loss is likely related to alterations in overall muscle mass and neuromuscular function. It has been proposed that lifestyle modifications to include exercise training and higher dietary protein intakes will likely be the most effective approach to offset muscle strength loss with advancing age. Thus, the study within this thesis aimed to examine the effect of manipulating the protein density of the diet in combination with resistance training on skeletal muscle strength and performance adaptations in middle-aged men and women. Fourteen healthy middle-aged adults were randomly assigned to consume protein at the Recommended Dietary Allowance (RDA; 0.8 – 1.0 g • kg BW-1 • day-1) or twice the Recommended Dietary Allowance (2×RDA; 1.6 – 1.8 g • kg BW-1 • day-1) throughout a supervised 10-week progressive resistance training program. Body composition, muscle strength and performance were evaluated pre- and post-intervention. Results of this study demonstrate that resistance training induced gains in lean body mass and muscle strength are not potentiated when consuming protein in far excess of the protein RDA in middle-aged adults. Thus, consuming protein slightly above the RDA (1.2 g • kg BW-1 • day-1) is adequate to support training-induced muscle adaptations when adhering to a healthy eating pattern consisting of equally distributed protein meals throughout the day