How Much of Your Protein Drink Does Your Body Keep?

Most protein advice is about how much to eat. Far less of it is about how much of what you eat your body actually holds on to as new protein. A 2020 study in the Journal of the International Society of Sports Nutrition measured exactly that. It compared a whey-based recovery drink with a drink built from free essential amino acids plus a small amount of whey, and tracked how much protein the body gained from each. The differences were large, and the reasons behind them say a lot about why protein quality matters as well as quantity.

What the researchers did

Park and colleagues studied 16 healthy young men and women at rest, after an overnight fast. Nobody trained during the study.

• One group of 8 drank a single serving (6.3 g) and, at least a week apart, a double serving (12.6 g) of the test drink. One serving held 3.2 g of free essential amino acids, 2.4 g of whey protein and 0.5 g of creatine.
• A second group of 8 drank a popular whey-based recovery product (17.9 g) that contained 12.6 g of whey protein.

Using stable isotope tracers, the team measured how fast the whole body built new protein and how fast it broke protein down over the 4 hours after the drink. The difference between the two is net protein balance: how much protein the body gained. They also took muscle biopsies to measure how fast muscle itself was building new protein.