Do you think we know everything about protein and how your body uses it to build muscle? Then you are sorely mistaken. We probably don’t know much at all. For example, we don’t know how long a certain amount of protein builds new muscle mass. Add all the various protein sources in a regular diet, and you have a very large amount of unknown data.
Most studies that examine muscle protein synthesis use isolated protein sources that you absorb very fast. Examples inlude whey protein and soy protein isolate. In addition, most of these studies look at whole body protein synthesis, not muscle protein synthesis in particular. Whole body protein synthesis includes everything in your body that use protein to create new tissue. Your organs, your gut, your skin, and so on, all rely on protein turnover. Nothing wrong with that. However, when you choke down a protein shake, you probably don’t care how much of that shake goes to building your intestines. That usually takes care of itself.
When you eat these fast acting proteins in isolation, the amino acid levels in your blood spike in minutes. This leads to a large and rapid increase in the amount of muscle protein your body creates. What happens when you eat a slowly absorbed protein, like when you eat a regular meal?
A New Study
In a new study, researchers had young men ingest 38 grams of milk protein concentrate. Milk protein concentrate is a mix of both slow and fast proteins. This creates an inflow of amino acids into your blood that is more typical to a regular meal, than chugging a whey shake.
The researchers gave the subjects continuous infusions of amino acid tracer infusions for 5 hours after they had ingested the protein. This makes it possible to follow the amino acids to see where they actually end up. In addition, they took repeated blood samples and biopsies during this 5-hour period and measured muscle protein synthesis and anabolic signaling.
The milk protein produced both a rapid and sustained increase in muscle protein synthesis lasting the entire 5-hour period. Amino acids quickly appeared in the blood, and the amount just kept rising.
During the first 2 hours, around 1.1 grams of the amino acids from the milk protein were incorporated into muscle protein. During the following 3 hours, another 1.6 grams of the amino acids followed suit and became new muscle protein.
This means that unlike a whey protein shake, where the stimulation of muscle protein synthesis only lasts an hour or three, protein absorbed more slowly bulids muscle a much longer time. This study only lasted 5 hours, but muscle protein synthesis was elevated the entire time. It might have gone on for quite a while longer for all we know.
What’s the take-away from this study? If you eat a regular protein-rich meal containing around 40 grams of protein, you don’t have to worry about building muscle for the next 5 hours. For at least the next 5 hours. You will have plenty of muscle-building amino acids available the entire time.