Postprandial Muscle Protein Synthesis Following Wheat Protein Ingestion in Vivo in Humans

Overview

Rationale: The progressive loss of skeletal muscle mass with aging, or sarcopenia, has a major impact on our health care system due to increased morbidity and greater need for hospitalization and/or institutionalization. One way to prevent skeletal muscle loss is to improve dietary intake of the elderly. Both whey and casein seem to offer an anabolic advantage over soy protein for promoting muscle hypertrophy. As a consequence it is assumed that (all) plant based proteins have less potent anabolic properties when compared with animal based proteins. However, there is little theoretical background for such assumptions. Objective: To provide evidence for the efficacy of wheat protein and wheat protein hydrolysate when compared with milk proteins (i.e. whey and casein) as a dietary protein to stimulate postprandial muscle protein synthesis in vivo in healthy older humans. Study design: double-blind, placebo-controlled intervention study Study population: 60 healthy non-obese (BMI 18.5-30 kg/m2) older males (age: 65-80 y) Intervention: A protein beverage (350 mL) containing 30 g of whey, casein, wheat protein, or wheat protein hydrolysate or 60 g of wheat protein hydrolysate will be consumed (n=12 per group). Main study parameters/endpoints: Primary study parameters include muscle protein synthesis rates. Secondary study parameters include whole-body protein synthesis, breakdown, oxidation, and net balance. Hypotheses: We hypothesize that ingestion of wheat protein hydrolysate results in a greater muscle protein synthetic response when compared with the intact wheat protein due to its faster digestion and absorption. Furthermore, ingestion of wheat protein hydrolysate results in a higher muscle protein synthetic response when compared with casein, but lower when compared with whey protein. Ingestion of 60 g of wheat protein hydrolysate (amount of leucine equal to 30 g of whey protein) will result in a similar muscle protein synthetic response compared to ingestion of 30 g of whey protein.

Aging is accompanied by a progressive decline in skeletal muscle mass. This age-related loss of muscle mass, or sarcopenia, is attributed to an imbalance between muscle protein synthesis and breakdown. As basal muscle protein synthesis rates do not seem to differ between young and elderly, most research has focused on potential impairments in the muscle protein synthetic response to the main anabolic stimuli, i.e. food intake and exercise. Skeletal muscle protein synthesis is highly responsive to food intake in healthy young adults. Recent data indicate that the muscle protein synthetic response to food intake may be blunted in the elderly. This proposed anabolic resistance is now being regarded as a key factor in the etiology of sarcopenia. Effective strategies to prevent and/or counteract the age-related loss of muscle mass include protein supplementation, preferably in combination with resistance exercise. Recent studies show the efficacy of dietary protein supplementation to improve muscle strength and function in frail elderly and to further augment the gains in muscle mass and function when combined with resistance exercise. As a consequence, nutrition research is now looking for the optimal amount, type, and timing of protein consumption to maximize postprandial muscle protein synthesis rates. Improvements in protein balance and/or higher muscle protein synthesis rates have been reported following the ingestion of various types of dietary protein: whey, casein, soy, casein hydrolysate, egg protein, and whole-milk and/or fat-free milk. It seems obvious to question which source of dietary protein is most effective in promoting muscle protein synthesis. There is only limited research comparing the efficacy of the ingestion of different proteins sources on the protein synthetic response. As such, it is difficult to identify a specific protein source that is most potentiating. This is further complicated by the fact that numerous parameters modulate the muscle protein synthetic response to protein ingestion. The amount and timing of protein administration, the amino acid composition of the protein, and the digestion and absorption kinetics of the protein source (or mixed meal), may all modulate the muscle protein synthetic response. Milk proteins, i.e. whey and casein, are the most widely studied dietary proteins. Casein and whey seem to have distinct anabolic properties, which are attributed to differences in digestion and absorption kinetics. Whey protein is a soluble protein that leads to fast intestinal absorption, whereas intact casein clots in the stomach delaying its digestion and absorption and the subsequent release of amino acids in the circulation. The faster, but more transient rise in plasma amino acid concentration after whey protein ingestion can lead to higher protein synthesis rates. In addition to intrinsic differences in digestion and absorption rate, it has been suggested that whey protein can more effectively stimulate protein synthesis due to its greater leucine content when compared to casein. Both whey and casein seem to offer an anabolic advantage over soy protein for promoting muscle hypertrophy. As a consequence it is assumed that (all) plant based proteins have less potent anabolic properties when compared with animal based proteins. However, there is little theoretical background for such assumptions. In this study we will assess the capacity of wheat protein ingestion as a means to increase postprandial muscle protein synthesis in vivo in humans. By directly comparing the anabolic properties of wheat protein or wheat protein hydrolysate with both casein and whey, we will determine the anabolic properties of wheat protein (hydrolysate) in vivo in older humans.