Many different numbers are perpetuated in this myth. Some “experts” claim you shouldn’t eat more than 40 grams of protein per meal, whereas others give lower numbers, and yet others higher.
Well, as with many issues of nutrition, there’s no simple answer.
It would stand to reason that an NFL linebacker’s body deals with protein intake differently than a 120-lb weakling’s. Protein needs due to lifestyle and lean mass should influence the matter of protein metabolism, right?
Additionally, if it were true that a person can only absorb a relatively small amount of protein in one meal, then “super-dosing” daily protein needs into 2–3 meals would result in protein deficiencies. This assumption begs the question of how the human species survived the hunter-gatherer days, but the body IS incredibly adaptive.
So, how much protein can we eat and absorb in one sitting, and how often do we have to eat protein to build muscle?
In order to better evaluate the issue at hand, let’s look at what actually happens when you eat protein.
First, your stomach uses its acid and enzymes to break the protein down into its building blocks, amino acids. These amino acids are transported into the bloodstream by special cells that line the intestines and are then delivered to various parts of the body. Your body only has so many transporter cells, which limits the amount of amino acids that can be infused into your blood every hour.
This is what we’re talking about with “protein absorption”—how quickly our bodies can absorb the amino acids into our bloodstreams.
It’s widely known that the human body absorbs different proteins at different rates. According to one review, whey clocks in at 8–10 grams absorbed per hour, casein at 6.1, soy at 3.9, and egg at 1.3. These numbers aren’t completely accurate due to the complexities involved in measuring protein absorption, but they lend insight nonetheless: certain proteins are absorbed very slowly, whereas others can be quite fast.
You should also know that food substances don’t move uniformly through the digestive tract, and they don’t leave sections in the same order that they arrived in.
For instance, the presence of protein in the stomach stimulates the production of a hormone that delays “gastric emptying” (the emptying of the food from the stomach), and that slows down intestinal contractions. This causes food to move more slowly through the small intestines, where nutrients are absorbed, and this is how your body buys the time it needs to absorb the protein you eat. Carbohydrates and fats can move through and be fully absorbed while your body is still working on the protein.
The next step in protein metabolism occurs once the amino acids make it into the blood stream. Your body does various things with them, such as tissue growth and repair, and it can temporarily store (up to about 24 hours or so) excess amino acids in muscle for future needs. If there are still amino acids in the blood after doing all of the above, your body can break them down into fuel for your brain and other cells.
If that’s how your body processes proteins we eat, what’s up with the claims that it can only absorb so much in one meal?
Claims that the body can only absorb so much protein in one sitting are usually based one or two things:
1. An ignorance of how food moves through the digestive system. Some people believe that all foods move through the small intestines in 2–3 hours. Thus, they believe, even if you ate even the fastest type of protein that can be absorbed at a rate of 8–10 grams per hour, you could only absorb 25–30 grams of protein in one meal. If you ate protein that is absorbed more slowly, then you would (apparently) wind up with even fewer grams absorbed into the bloodstream.
Well, as we now know, your body is smarter than that, and regulates the speed at which protein moves through the small intestines to ensure it can absorb all of the available amino acids.
2. References to studies relating to the anabolic response to protein consumption. A study commonly cited in connection with protein absorption showed that 20 grams of post-workout protein stimulated maximum muscle protein synthesis in young men. That is, eating more than 20 grams of protein after working out did nothing more in terms of stimulating muscle growth.
The most obvious flaw in this argument is you can’t use studies on the anabolic response to protein consumption to extrapolate ideas about how much we can absorb in one sitting. Acute anabolic responses to eating protein don’t give us the whole picture. Absorption relates to the availability of amino acids over extended periods of time, which prevents muscle breakdown and provides raw materials for growth. And, as we now know, our body doesn’t just throw away all of the amino acids it can’t immediately use—it can store them for later
Further supporting this position is a study conducted by the Human Nutrition Research Center. It had 16 young women eat 79% of the day’s protein (about 54 grams) in one meal or four meals over the course of 14 days. Researchers found no difference between the groups in terms of protein synthesis or degradation.
Furthermore, if we look at the amount of protein used in the above study relative to body weight, it comes out to about 1.17g/kg. Apply that to a man weighing 80 kilograms (176 pounds), and you get about 94 grams of protein in one sitting. While this isn’t definitive scientific proof, it’s food for thought.
Research on the style of dieting known as intermittent fasting is also relevant. This style of dieting has people fasting for extended periods, followed by anywhere from 2–8-hour “feeding windows.” One study found that eating the entire days’ worth of protein in a 4-hour window (followed by 20 hours of fasting) didn’t negatively impact muscle preservation.
Before we move on, I want to quickly address something mentioned earlier, which is the study that showed that 20 grams of post-workout protein stimulated maximum protein synthesis in young men. Don’t assume that this 20-gram number applies to everyone.
Protein metabolism is affected by several things:
On the other hand, elevated levels of cortisol reduces protein synthesis and accelerates the process whereby the body breaks down amino acids into glucose (gluconeogenesis), thereby reducing the amount available for tissue generation and repair. Some people have chronically elevated cortisol levels, and this impairs protein metabolism.
So, while 20 grams of protein might be enough to stimulate maximal muscle growth in certain conditions, this won’t hold true for everyone. Some people will need more to reach the same level of synthesis, and others will be able to benefit from more protein (it will result in more protein synthesis).
As you can see, it’s impossible to put a cap on how much protein your body can absorb in one meal. It’s definitely a hell of a lot more than the 20–30 grams that some people claim.
You probably also noticed that protein timing isn’t as important as some people think, either. You don’t have to eat protein every 2-3 hours to maximize muscle growth or avoid going catabolic. Total intake over 24-hour periods is what really matters, not regular feedings.
While it’s smart to have a good amount of protein before and after training, break up the rest of your daily needs however you want and let your body take care of the rest.
Personally, I like to eat every few hours, but if you prefer fewer, larger meals, then don’t be afraid to load up on the protein when you eat.