The Truth About Protein Absorption 

Some misconceptions and half-truths just seem to stick around, and this is one of them: "If I eat more than X grams of protein in one meal, then the 'excess' will go to waste."

Is that really the case? Is there a ceiling to the amount of protein our body can successfully "absorb" (which frankly, could mean a lot of things) in one sitting? 

We'll call this a half-truth, because there does appear to be an upper limit or "saturation point" when it comes to protein consumption in one meal as it pertains to muscle protein synthesis. But while muscle building is often the primary focus of individuals looking to increase their protein intake, protein plays a far larger role in the body than simply building muscle mass.

Protein is crucial for all bodily tissues, and while we do not have a system for storing protein (similar to how carbs or fats are stored) the body does not simply reject all protein consumed beyond a certain limit. There is no biological gate that only allows say, 30g of dietary protein to pass at one time before slamming shut and sending the rest of the protein you ate straight to your toilet bowl.

So let's first discuss the truth portion of the half-truth mentioned above, and the limitations of protein consumption in relation to building muscle.

Reaching the Point of Diminishing Gainz

To begin, we need to define what "absorption" actually entails. From a nutritional standpoint, absorption describes the passage of nutrients from the gut into systemic circulation. By this definition, the amount of protein the body can absorb is virtually limitless.

After protein passes through digestion, the constituent amino acids the protein source is made up of pass through the liver, which utilizes some of the aminos directly. The remaining amino acids not utilized by the liver then pass into the bloodstream, where they become available for use by bodily tissues.

But how much is utilized by our muscles?

The bulk of research suggests that protein consumed beyond approx. 20-25g in one meal likely does little to further increase muscle protein synthesis. However, there are a number of factors that may affect dietary protein metabolism, ranging from the type of protein source, the amount ingested, other nutrients consumed, and how trained an individual is.

In addition, some debate still exists regarding the "anabolic ceiling" of 25g per sitting. A 2016 study published in Physiological Reports found the muscle protein synthesis response to 40g of whey protein ingested following whole-body resistance training was greater than 20g of whey ingested following the same workout. Researchers suggested the full-body nature of the workout may prompt a greater demand for amino acids than exercise focused on one muscle group.

"So, you're saying my muscles are hungrier for protein following my heavy leg day?" Possibly, but the research is still mixed. 

A 2018 paper published in the Journal of the International Society of Sports Nutrition suggests that in order to maximize anabolism over the course of a whole day, resistance-trained individuals should aim for 0.4g protein per kg of body weight (0.18g/lb), split between four meals. This suggestion is consistent with the generally accepted daily protein intake of 1.6g/kg of body weight, or 1g/lb to maximize muscle building.

What Happens to The Rest?

What happens to "excess" protein consumed beyond that 20-25g can largely depend on the unique digestion speed of the protein source. It appears that when consumed alone, fast-digesting protein sources like whey are more likely to be oxidized and utilized for energy, after muscle protein synthesis has been maximized. 

Slower-digesting protein sources, like casein, egg, plant protein, or protein consumed along with other macronutrients are likely assimilated almost entirely by the body due to their slower digestion speed. The "surplus" amino acids not utilized for MPS pass through digestion and are then utilized by the liver, or enter the bloodstream where they are available for use by bodily tissues for a number of different tasks. Our bodily structures are largely made up of protein, so there is always a demand.

The reality is, most individuals are in no danger of over-consuming protein, if there is such a thing. Those with impaired kidney function may need to be mindful of excess protein intake (a topic for another day), but many people fall on the opposite end of the spectrum and aren’t eating nearly enough.

However, individuals in the weight training and bodybuilding spaces may find themselves thinking “If some is good, more must be better” in terms of their post-workout protein shakes or protein rich meals.
Unfortunately, double-scooping your whey protein supplement post-workout is unlikely to produce double the gainz. That said, a meal containing 50g of high-quality protein does not go half to your muscles, and half to s**t.