The effects of protein type and added leucine on post-exercise muscle protein synthesis

Rationale: Dietary protein intake after exercise is necessary to maximally stimulate muscle protein synthesis rates. Data demonstrate that the type/source of protein consumed (e.g., animal vs. plant-derived proteins) can impact the amplitude and duration of muscle protein synthesis during post-exercise recovery. Specifically, bovine milk proteins stimulate greater rates of muscle protein synthesis after resistance exercise than consumption of an isonitrogenous soy-protein beverage. The major proteins in bovine milk are casein (~80%) and whey protein (~20%). In their isolated forms, these proteins greatly differ in their digestion and absorption kinetics. Whey protein is rapidly digested and absorbed leading to a pronounced, rapid, but transient peak in plasma amino acid levels and robust stimulation of protein synthesis. On the other hand, isolated casein is a slowly digested protein that results in a slower, moderate, but more prolonged increase in plasma amino acid availability resulting in a greatly attenuated protein synthesis response compared to whey. No studies have compared the muscle protein synthesis response following bovine milk as compared to its constituent proteins whey and casein. Further, whether the post-exercise muscle protein synthesis response to soy protein can be enhanced when the leucine content of soy is matched to milk remains unknown. We aim to fill this gap in our understanding.
Objective: To define the properties of whey, casein, milk protein, as well as soy protein with and without additional leucine to augment post-exercise muscle protein synthesis when co-ingested with a carbohydrate containing recovery drink.

Study design: Parallel group, randomized, placebo controlled, double blind.

Study population: 72 young (20-30 y inclusive) healthy males.

Intervention: Subjects will perform both aerobic and resistance exercise and consume either a carbohydrate solution or a carbohydrate solution with 20 g whey, 20 g casein, 20 g milk protein, 20 g soy protein, or 20 g soy protein with leucine. In addition, continuous intravenous tracer infusions will be applied, with plasma and muscle samples collected.

Main study parameters/endpoints: Primary: mixed, myofibrillar, and mitochondrial protein bound [13C6] phenylalanine enrichments. Secondary: plasma glucose, insulin, leucine, phenylalanine, tyrosine, plasma [13C6]phenylalanine and (3,5-D2)-tyrosine enrichments.

Protein-carbohydrate ingestion stimulates greater muscle protein synthesis than carbohydrate placebo alone. milk and whey protein elicit the greatest anabolic response. Soy protein with added leucine will stimulate muscle protein synthesis equivalent to whey protein

t=0 Drink. t=0 , t=2h and t=6h muscle biopsies. 14 blood draws

Exercise bout followed by ingestion of one of the following beverages:

• Carbohydrate drink (45 g Carbohydrate)

• Carbohydrate drink (45 g Carbohydrate) with 20 g milk protein

• Carbohydrate drink (45 g Carbohydrate) with 20 g whey

• Carbohydrate drink (45 g Carbohydrate) with 20 g casein

• Carbohydrate drink (45 g Carbohydrate) with 20 g soy

• Carbohydrate drink (45 g Carbohydrate) with 20 g soy and leucine