How much protein can we absorb per meal?

Carlos Sánchez 8 min. of reading Proteins Leave a comment

Protein intake has become one of the most influential factors for the scientific community when we talk about body composition

Greater muscle mass during a low-calorie diet (1) or a reduction in appetite (2) (and therefore calories consumed) are some of the positive effects shown by increasing protein intake in the diet.

Still, the topic of proteins is very broad and debated, raising questions like:

How many grams of protein is optimal,
What type of protein we should consume and, the one that creates the most disagreement,
How to split protein intake across different meals.

In this article, I’ll focus on this last point and see if the number of meals affects better or worse amino acid absorption

The myth of absorbing 30g per meal

As many of you know, the protein we eat through food is digested in our digestive tract, resulting in amino acids or di- and tripeptides (bonds of two or three amino acids).

If you remember my article about peptides, I mentioned that hydrolyzed protein intake has a faster absorption rate than other proteins since di- and tripeptides are absorbed through a different type of receptor (specifically via PEPT1) (3), avoiding saturation of the common sodium-dependent receptors.

Obviously, gastric emptying has a big impact on the absorption speed of different amino acids

High-fat meals, solid foods, or very large volumes of liquids are some factors that can delay gastric emptying and therefore reduce absorption

This phenomenon has made many obsess over finding the fastest way to take their post-workout shake, a topic I recently covered.

The problem we find is that athletes confuse the term “absorb” with “use”

Nutrient absorption

Nutrient absorption by our body is a very efficient process

We’re talking about absorption close to 95% (6), with the remaining 5% usually used by our bacterial flora or expelled with the feces.

A clear example is seen when comparing the effects of eating one meal a day versus 3 (4).

There’s no difference in hormones like insulin or adiponectin, which are related to carbohydrate and fat availability

Amino acid absorption

In the case of amino acids, a large part is retained (around 30-50%), with preference for two amino acids in particular: Glutamine and Aspartate (the form in which aspartic acid can be found).

When our body doesn’t get proteins or glucose intake is very low, our intestinal cells start releasing amino acids to be used (5), preventing the need to break down muscle mass.

Relax, losing muscle is harder than you think…

As I mentioned above, our body is one of the smartest machines out there, and the intestine is no exception.

When protein intake is very high, amino acid absorption is limited (due to saturation in transport into cells), increasing the amount of amino acids flowing into the colon.

As you can guess, reducing protein intake to one meal isn’t ideal for people with damaged intestinal mucosa, as it will make proper amino acid absorption harder.

Diagram of the amino acid “pool” at the intestinal level

When protein intake is low, our intestinal cells will release amino acids, which is why having a healthy mucosa is essential for our protein metabolism (Marielle P et al 2007)

Protein utilization

Having covered absorption, now comes utilization (which is why I stressed the difference earlier). Amino acid utilization depends largely on two factors:

The protein quality
The type of protein (fast VS slow)

Protein quality

In the first case, protein quality will determine the greater or lesser retention of amino acids at the intestinal level, with a classic example being the comparison between soy VS casein or Whey Protein – The Whole Truth About Whey Protein.

When comparing both proteins, soy protein is converted into urea, while casein tends to increase protein synthesis, reducing urea production (9).

Although both proteins reduce protein breakdown (commonly known as catabolism), the biological value of the protein will determine the greater or lesser protein synthesis at the muscle (and systemic) level, with proteins like WHEY being superior to plant-based ones like soy.

Type of protein

In the second case, the speed of the protein also influences amino acid utilization. As most of you know, WHEY protein is a fast protein, so it spikes amino acid levels in the bloodstream, unlike a slow protein like casein, which releases amino acids much more gradually.

So, if someone consumes little protein, casein will be better for them by maintaining a positive nitrogen balance for longer hours (10), as shown in the image below.

Casein keeps leucine levels up longer. Chart adapted by S.Espinar from Boirie et al.

However, we have to be aware that nobody eats just one meal a day (except some who practice intermittent fasting), so this isn’t a real situation.

When protein intake is every 4-5h, the “advantage” of slow proteins disappears, since amino acids are supplied constantly, so slow protein intake is only interesting for older adults

Conclusions

In summary, most experts agree that the higher the presence of amino acids in the blood, the greater the muscle protein synthesis and, therefore, the greater the muscle mass gained

Which is partly true:

It’s true that amino acid presence at the muscle level is a key factor for muscle growth, but it’s not the most important
What some studies (11) show is that the amount of intracellular amino acids has no relation to greater protein synthesis (yes, you read that right) because they saturate easily

Origin of the Myth

The amount at which this “anabolic environment” is maximized is approximately 30g

That’s why it’s confused with absorption and has given rise to the myth that we can only absorb 30g of protein per meal, something disproved by this article.

In fact, putting most protein in one meal can be an option for older people, since it’s been observed that consuming 80% of protein in one meal improves muscle mass (12).

This should not be extrapolated to healthy or athletic populations, hence my recommendation to split protein intake into at least 3 meals (for convenience), possibly increasing it for satiety reasons (don’t forget protein is the most satiating macronutrient).

Don’t obsess over forcing yourself to eat protein every 2-3h, remember that the most comfortable diet for you is the one you can stick to the longest

Cheers!

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