Habitual Protein Intake and Muscle Protein Synthesis
Condition: Sarcopenia
MeSH terms: Sarcopenia
Study type: Interventional

Summary: 
      Protein intake stimulates muscle protein synthesis. From the standpoint of maintaining
      skeletal muscle mass with aging, it is important to optimize the adaptive response to food
      intake. However, a paucity of information is available describing the effects of habitual
      dietary protein intake (i.e. either high or low amounts of dietary protein consumed on a
      regular basis), on the subsequent meal-induced stimulation of muscle protein synthesis. An
      adaptation to a diet of several days or weeks may involve splanchnic and/or skeletal muscle
      adaptations that may further enhance, or decrease, the amino acid sensitivity of muscle
      protein synthesis after protein ingestion.

      The aim of this study is to investigate the effect of a habitual (14 days) high protein diet
      when compared with low protein diet on digestion and absorption kinetics and the subsequent
      muscle protein synthetic response to dietary protein ingestion.
    

Detailed description: 
      During the adult life skeletal muscle mass remains fairly constant until the fourth or fifth
      decade. Then, the slow process of sarcopenia (the age-related loss of muscle mass) is
      believed to begin. The maintenance of skeletal muscle mass is regulated by a balance between
      the opposing processes of muscle protein synthesis and muscle protein breakdown. Food intake,
      dietary protein in particular, stimulates muscle protein synthesis and allows net muscle
      protein accretion throughout the day, which allows the normal maintenance of muscle mass in
      healthy individuals. Many studies have described the postprandial muscle protein synthetic
      response to protein intake and/or physical activity, and these acute findings have led to
      recommendations for protein intake for both athletes wishing to gain muscle mass as well as
      patients and elderly individuals to help them maintaining muscle mass. However, translating
      the acute findings from a single meal to long-term recommendations is perhaps premature,
      since scientists know very little with regard to how previous consumed meals affect the
      anabolic responsiveness to subsequent food intake. A characteristic of the adaptation to
      habitual high or low protein intake is thought to be associated with a change in the
      amplitude of diurnal cycle of whole body proteins. If this speculation is accurate, it
      implies that the muscle protein synthetic responses to feeding (differences between fasting
      and feeding muscle protein synthesis rates) are adapting to differing habitual protein
      intake, which may reduce (or enhance) the anabolic responsiveness to protein intake.

      To gain a more complete scientific understanding, it is necessary to examine whether an
      adaptation does in fact occur after habitual high or low amounts of protein intake with
      regard to the anabolic response to subsequent protein intake. In the present investigation,
      we wish to investigate the impact of the habitual consumption of either high or low protein
      diets for 14 days on the anabolic responsiveness to a protein meal in healthy elderly.
      Previous work has determined that whole body adaptations to protein intake occur after >10
      days. Collectively, our findings will be valuable to maximize the skeletal muscle adaptive
      response to food intake and, ultimately, to develop nutritional strategies for maintenance or
      enhancement of skeletal muscle mass in elderly men.
    

Intervention name(s): Protein diet
Intervention type(s): Dietary Supplement
Intervention description(s): Subjects will receive either a low protein or a high protein diet for 14 days. High protein will be realized with protein supplements.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Prevention
Keywords: Muscle protein synthesis; Digestion and absorption kinetics; Leucine; Whey protein