Gut amino acid absorption in humans: concepts and relevance for postprandial metabolism

Our new review:
Gut amino acid absorption in humans: concepts and relevance for postprandial metabolism

*Note: this is a methodological review. Therefore, it is not focused on practical takeaways. But feel free to ask your protein questions in the comments*

Not all dietary protein has the same nutritional quality. An important factor that impacts protein quality is its absorption in the gut.  

For example, protein powders have a very high absorption (~95%), while whole food plant-based proteins are typically lower (~70%).

We found that much of the literature discussing protein absorption is confusing, inconsistent, and/or incorrect.

For example, digestibility, absorption, release in the circulation, and bioavailability seem to be used interchangeably, while we consider them all different. See the table below for the definition we propose:

Hence, the common term “amino acid digestibility” is a misnomer. Amino acids are not digested, they are absorbed. “Amino acid absorbability” is clearer and more accurate.

The same is true for the various essays used to assess gut absorption.

Apparent, standardized, true, and real ileal digestibility are used inconsistently. As a consequence, this inconsistency and inaccuracy spills over to protein quality scores.

Another limitation of protein quality scoring systems (e.g. DIAAS) is that they account for total absorption, but not absorption rate.

However, a more rapid absorption may result in a greater anabolic response.

Therefore, a kinetic approach is preferred to take into account all experimental and individual factors.

Postprandial whole-body protein net balance can only be assessed using intrinsically labeled protein, but the method is expensive and complex (Trommelen, 2021).

In summary,

• There is a need for more consistency and accuracy in the terminology of protein digestion and amino acid absorption.
• Protein quality scoring systems have limitations.
• Intrinsically labeled protein can accurately assess the anabolic response.

Open access reference:
Trommelen et al, Clinical Science Open Science, 2021