From the time that the first physique enthusiasts & bodybuilders ever started choking down extra chicken breasts, steaks, and vile concoctions to increase their protein intake for the purposes of gaining muscle; the question of just how much protein is optimal has been debated. Fast forward more than half a century and people still debate the same question without much of a consensus. Many people believe that protein is already over consumed by the typical person and bodybuilders and athletes have no need to take in extra, while there are those who will tell you that there is no upper limit to the benefits of protein. In reality the answer to this question probably lies well within the middle of these two extremes. The question of protein quantity at a meal and frequency of protein consumption has been debated almost as often as total protein consumption. Quite often we see the question, “what is the max level of protein that one can benefit from at a meal and how long often should I consume it?” Fortunately for us, this question actually has some data that we can start picking apart to get some general guidelines for protein size and frequency at meals.
Many ‘experts’ or gym know-it-alls out there who will tell you to only consume “X” amount of protein at a meal because only “X” amount of protein can be absorbed by the body at a meal (I’m sure you’ve all heard this one before). Let this nonsense stop here and now. To begin with, this entire train of thought isn’t even on the correct track. Hell it didn’t even depart from the right train station! Assuming that you have a healthy digestive system, the absorption of the amino acids from a meal containing protein is very efficient and almost never a limiting factor. Absorption only refers to nutrient uptake & absorption via the digestive track (most absorption occurring in the small intestine). If our digestive systems didn’t absorb most of what we eat than anytime you had a big meal you would have diarrhea like clockwork from the undigested material in the gut! It also makes very little sense from an evolutionary standpoint to be very wasteful with nutrients when primitive man may have only been able to eat one large meal in a day at times. Our species would not have survived very long if we were wasteful with nutrients and did not absorb amino acids beyond a certain level. In reality, the body has an extremely high capacity for amino acid absorption. What these people who spout this nonsense are really referring to is amino acid utilization. You see, even if we absorb 100% of the amino acids we ingest, that doesn’t mean they will all reach the skeletal muscle and input towards building muscle mass. In actuality a very small percentage are used for that role. The cells of the small intestine and liver extract a huge amount of amino acids for energy and their own synthesis of new proteins in first pass metabolism before they ever reach the bloodstream! Once in the bloodstream amino acids can also be taken up and utilized by other tissues such as the kidneys, heart, skin, etc. So it is not a question of how much protein/amino acids can be absorbed at a meal, rather the question is what level of protein at a meal gives the maximum benefit for muscle building? Essentially anything below this level would not maximally support muscle building, while at a protein intake above this level, the body would merely oxidize the excess amino acids for energy.
In order to start answering this question of optimal protein intake at a meal we first must make clear as to what defines a “maximum level of benefit” from protein intake. Using rates of protein synthesis as a measure for this definition is logical as increased rates of protein synthesis would be required for the addition of new skeletal muscle tissue. To put it more plainly, in order to build muscle the body must increase the rate at which it synthesizes muscle tissue above the baseline rate. Decreasing the rate of skeletal muscle breakdown also can lead to increased tissue accrual, unfortunately data on protein breakdown is much more difficult to obtain, interpret, and it is much more variable than the synthesis data. It is very difficult to measure short term changes in skeletal muscle breakdown as it has a very slow turnover rate so the focus on this article will be on protein synthesis, which likely plays more of a regulatory role in tissue accrual/loss in muscle than degradation since synthesis is the more regulated energy dependant process.
To find the optimal level of protein intake at a meal we must determine what the optimal level of protein at a meal for stimulating muscle protein synthesis is. It appears that maximizing skeletal muscle protein synthesis requires approximately ~15g of an essential amino acids1,2. It has been postulated that the amino acid leucine is responsible for the stimulatory effect of dietary protein on protein synthesis3 and 15g of essential amino acids would contain 3.2g of leucine. Thus in order to determine how much protein from a specific source is required to elicit the maximal response it may be useful to back calculate how much leucine is contained in the source. One could then determine how much of the source must be consumed in order to reach the leucine threshold. For example, whey protein is approximately 12% leucine per gram protein, therefore about 27g of protein from whey would need to be consumed to reach the threshold for maximal anabolism, whereas a source like chicken, which has a protein content of about 7.5% leucine would require 43g of protein to reach the leucine threshold required for maximal stimulation. So it appears that the maximum benefit level for protein at a meal is varies depending upon the source of protein. It is important to note that most of these studies were done on individuals who weighed approximately 155-165 lbs on average. So if you weigh less than this you might want to aim for the lower end of the threshold whereas if you weigh more you may want to aim for the higher end of the threshold.