Protein Metabolism: How Much Protein Can Your Body Absorb at Once
You might have heard of the claim that the human body cannot absorb more than a limited amount of protein at a time, and anything from 20 to 40 g is usually quoted as the upper limit of that amount (which is what 100 to 200 g meat would provide you with), and that if you eat more protein than that in a single meal, the rest of it will go to waste.
Is there any truth to that, though? Should you be eating only limited amounts of your protein source of choice at any given time?
How about people who have higher protein requirements, for example 150 g or more, such as athletes, or highly active people, or people who have lots of muscle. Do they need to eat their protein in 5 or 6 small portions throughout the day? Will they be unable to gain more muscle if they don’t?
Let’s see what the science says.
How Is Protein Absorbed By The Body?
Protein is made up of a number different of substances called amino acids, which are the building blocks of your body, and as such, an essential part of any diet or way of eating. Not only your muscles are made of protein, but also all other tissues, organs, hair, and even the hormones and enzymes.
Nine of the twenty amino acids are called “essential”, as the body cannot synthesize them, and are contained in high quality protein sources, such as meat, fish, eggs and dairy. They can also be found to varying extent in plants, but in that case the different plant sources would need to be combined so that your body can have a sufficient quantity of all nine essential amino acids.
When you consume a food containing protein, it gets broken down into its amino acids in your stomach. After that, the amino acids are absorbed into the bloodstream by cells in the small intestine, and then get “dispatched” to whichever parts of your body need to be repaired and rebuilt (for example, your muscles after a resistance workout, but also all of your organs and tissues).
Additionally, digestion is slowed down when the presence of a big amount of protein is detected.
Is There An Upper Limit To Protein Absorption For Maximizing Muscle Growth?
It’s important to mention that studies on protein absorption are somewhat lacking in accuracy, because it is impossible, for the moment, to trace the exact fate of the amino acids, once they’re absorbed in the small intestine into the bloodstream.
Most studies rely on information about intake and output, or on nitrogen excretion through urine, which means that the fine details of what happens exactly are lost.
Nevertheless, we do have a good understanding of the speed at which protein is absorbed, and it is hugely dependent on the type of protein.
Whey, for example, which is one of the proteins with the fastest absorption rate, is absorbed at approximately 8 to 10 g per hour, while casein comes at 6.1 g/h, and cooked egg whites at 2.9 g/h (4, 5).
As you can see, there isn’t a single “speed of absorption of protein”, but rather, a number of different values based on the type.
Another important thing to consider is that not all nutrients move through the intestine at the same speed. The body can absorb carbs and fat quickly, while at the same time delaying protein absorption, in order to maximize it.
The term “absorption” refers to the amount of amino acids that can be transported from the small intestine into the bloodstream, and this amount is nearly unlimited.
The real question is, how much of the absorbed protein is used for muscle repair and retention, and how much of it is used for other tissues.
Most meals are made of a mix of protein, carbs and fat, and your body will regulate the speed at which protein is absorbed. Meals high in protein will have an anabolic effect on the body for approximately 5-6 hours (6).
Bigger meals are slower to digest, and therefore the nutrients in them take longer to be fully absorbed – which is also why having 1, 2 or 3 big meals instead of 6-8 smaller ones, including snacks, feels more satisfying for most people.
So unless your main protein source is whey, you don’t need to be concerned – protein takes time to absorb, and the digestive system can slow the whole process down when you eat a lot of protein at once, especially if you combine it with other macronutrients.
For young women, both feeding patterns had a similar score in terms of protein retention, and that receiving most of their daily protein at once did not have a negative effect on protein synthesis and breakdown (9).
Studies on intermittent fasting show similar results – one study points out that intermittent fasting combined with calorie restriction, when compared to daily calorie restriction, might give better results in terms of muscle mass retention (10).
Another study on the OMAD (one meal a day) diet concluded that this way of eating might have a slight benefit in terms of body composition (11).
A study from 2016 on a 20:4 fasting protocol and a control group, combined with resistance training, showed that the increase in muscle mass (whereas measurements of the biceps brachii and rectus femoris muscles were taken), as well as in bench press strength was similar for both groups (12).
Additionally, as far as the anabolic response to protein ingestion is concerned, a study from 2014 points out that there virtually isn’t a limit to the maximum anabolic response after a meal, even when big amounts of protein are consumed (13).
Keep in mind that the net anabolic response (i.e. how much muscle you’d be able to gain) is also dependent on the protein breakdown, and not only on protein synthesis – both are constant processes in your body and are incredibly complex as such. At higher levels of protein availability, no upper limit in the anabolic response has been observed.
To complicate matters a little more, the same study points out that for optimal muscle protein synthesis to be provoked, it is necessary to consume more than 30 g protein at once.
So if you want to build muscle and provide your body with the best conditions to do so, you should aim to consume upwards of 30 g protein at once (which isn’t so difficult – 150 g of most meats measured raw would provide you with approx. 30 g protein).
If you’re concerned with whether your body can deal with more than 30 g protein at a time, don’t worry – our bodies are very smart and well-equipped to survive, optimize performance and utilize precious and scarce resources (which protein used to be when we needed to hunt for it) in the most effective way.
Small differences might exist, regarding meal timing and optimal protein synthesis, however, these are certainly subtle, and much less significant than sticking to your macros and to the protein you need in order to function and to sustain your lean body mass.
The most important part of the equation is eating adequate protein; meal timing and distribution through the day – much less so. If you eat a higher amount of protein at once, anything above 30 g will definitely not be wasted.
The real questions that you need to answer for yourself are: are you eating adequate protein? Are you sticking to your daily calories systematically? Are you accurately tracking your calories and macros? Are you doing some sort of resistance training, such as weightlifting? Are you giving your body adequate rest between workouts?
If the answer to these questions is “yes”, then you are definitely on the right track to improving your body composition and performance, and how you schedule your protein consumption throughout your day will not be nearly as important as any of these conditions.
If you’d like to make the best out of your protein consumption, it’s advised to not rely only on fast absorbing protein sources, such as whey, but instead to have a variety of high quality protein sources that are slower to digest, such as meat, dairy and eggs, and to eat your protein in combination with other nutrients (i.e. protein shakes , protein powders or collagen peptides can be an okay solution if you’re in a hurry, but they shouldn’t make up a major part of your day to day protein consumption).
On top of that, to elicit an optimal response in terms of muscle synthesis, it’s best to consume at least 30 g of protein at a time, but again, the details are so complex and studies haven’t yet reached a definite conclusion, that if you make sure to hit your protein macro daily (remember, “protein is a goal”), you’d likely benefit from all types of protein distribution throughout the day.
Personal preferences are also an important factor – if you feel best eating one or two big meals a day and like to consume most of your protein within these meals, that’s completely okay and you are unlikely to risk losing muscle mass, or miss on muscle gains.
What are your personal preferences in terms of protein consumption?
Would you rather eat all of your protein at once, or spread it out evenly?
Are you doing intermittent fasting? Are you doing OMAD?
Share your experience with us in the comments below!