On the other hand, Nelson points out that the amount of amino acids that can be used to fuel muscle growth2, or muscle protein synthesis (MPS), is limited.
He compares the process of muscle hypertrophy (aka muscle building) to an assembly line: A calorie surplus is needed to provide energy for the line, leucine (a type of branched-chain amino acid) is needed to turn it on via a gene called mTOR, and essential amino acids are used as the building materials for the new muscle tissue.
“Levels of leucine above 2.5 grams per meal will turn on [mTOR],” protein and amino acid requirements researcher Don Layman, Ph.D., explains on the mindbodygreen podcast. “If you don’t meet that threshold, that protein consumption is a sense going to waste.”
This means that the composition of your meal matters just as much as how many grams of protein you’re getting in your daily diet.
There are a few other factors that can also impact how much protein your body is able to use for muscle growth1, including your age, body composition, and training status.
Interestingly, one 2015 study estimated that the amount of protein needed to maximize muscle growth3 was up to 0.4 gram per kilogram of body weight for young men, and up to 0.6 grams per kilogram for some older men. To put this into perspective, this means that a 150-pound man can require up to 27 to 41 grams (including 2.5 grams of leucine) to maximize hypertrophy, depending on their age.
Mary Sabat, M.S., RDN, L.D., points out that your overall protein needs can be influenced by a wide range of factors4, including your age, your physical activity level, the intensity and duration of your workouts, and your overall health status. Learn more about figuring out your personal protein needs here.
