by Jeff S. Volek, Ph.D., R.D.
This is a difficult question to answer because not only does the amount of protein affect muscle mass, but also the type of protein and timing of ingestion. A couple of recent papers provide results that help advance our knowledge of how best to incorporate protein into the diet.
There have only been a few dose-response studies to determine what dose of protein elicits the optimal increase in muscle protein synthesis, one in young people and one in older people. Both used whey as the protein source. The young resistance-trained men were fed 0, 10, 20 or 40 grams of protein after performing a bout of resistance exercise. Compared to the control trial (0g protein), the rates of muscle protein synthesis were significantly higher with the 20g (49%) and 40g (56%) dose, but not the 10g dose.
In a study of older individuals (average age of 70 years), muscle protein synthesis was determined after performing a bout of resistance exercise followed by ingestion of a drink containing 0, 10, 20 or 40 grams of whey protein isolate. There was a significant increase in muscle protein synthesis with 20 grams of whey, and a further 32% increase with the 40 gram dose. Leucine oxidation (indicating protein was being burned as fuel) increased in a step wise manner as the dose of whey increased.
These studies support the idea that at least 20 grams of an intact quality protein source, and maybe closer to 40 grams for older individuals, is necessary to achieve a maximal increase in muscle protein synthesis after resistance exercise. Adding carbs to the protein does not appear to offer additional benefit on muscle protein synthesis.