protein absorption rates

Protein Absorption Rates

Understand protein absorption rates to support muscle growth and recovery

Bioavailability is the standard used to determine which protein supplement is best to support your muscle recovery and growth after training.

Bioavailability refers to how much of the protein you consume actually reaches your bloodstream so your muscles can use the circulating amino acids for growth and repair.


Know your biological values

A key metric often used to quantify protein bioavailability is biological value (BV), which is a measure of how efficiently the body can use a protein source to build and repair muscle tissue.

It is calculated by comparing the nitrogen retained in the body from a protein source to the nitrogen consumed. A higher biological value indicates a more efficient protein source, which typically supplies all the essential amino acids (EAAs) that your body can’t produce on its own.

Animal proteins typically possess a higher BV than plant sources due to the lack of one or more EAAs in plant-based proteins.

The biological value of protein supplements:

  • Whey protein: 104
  • Eggs: 100
  • Milk: 91
  • Casein protein: 77
  • Soy protein: 74

Whey achieves slightly better nitrogen retention than soy or casein, likely due to its high EAA content, especially leucine².


The protein digestion journey

Protein digestion starts in your mouth, where enzymes in saliva start breaking the bonds that bind amino acids together into protein molecules.

Once in the stomach, a digestive enzyme called pepsin starts to break down chains of connected amino acids called polypeptides into smaller peptides.

The pancreas releases additional digestive enzymes into the small intestine, which continue to break down peptides into smaller peptides (tripeptides and dipeptides) and individual amino acids3 in the upper part (the duodenum).

Following digestion, protein absorption occurs in the middle and lower parts of the small intestine, in the jejunum and ileum³.

The time it takes for the body to absorb the single amino acids digested from whole proteins varies significantly between sources.


Whey and casein

Amino acid concentrations rise rapidly after drinking a product like Primal Whey Protein, peaking roughly within 100 minutes and returning to baseline within 300 minutes ⁴.

Rates also vary between whey variants, with whey isolate taking 60-90 minutes to digest and whey concentrate between 2-3 hours.

Based on findings from a 2001 study⁴, amino acid levels started rising after 20 minutes and remained elevated for 180–200 minutes among those who consumed the amino acids and whey protein.

The body absorbs casein from supplements like Primal Premium Casein more slowly taking 3-7 hours to fully digest, with amino acid concentrations remaining elevated beyond five hours⁴.

In the 2001 study, it took 20–40 minutes for amino acid levels to rise after participants consumed casein and remained elevated for seven hours (all participants consumed a 30g serving of protein).


Egg protein

A product like Primal Egg Protein Powder is another animal-derived protein supplement with a similar biological value to whey (104 vs 94) and a moderate absorption rate of between 3-5 hours.

Egg protein has a complete amino acid profile, including all nine EAAs.


Protein blends

A 2012 clinical study⁶ confirmed that consuming a blend of proteins (whey and casein) versus whey protein alone “provides a prolonged delivery of amino acids to the muscles, making it optimal for consumption following resistance exercise.”

Protein blends like Primal Blended Whey deliver a varied and prolonged absorption profile, offering the best of all proteins, which makes it ideal for those looking to prolong the amino acid release between meals.

Whey provides a quick release of amino acids whereas plant-based sources like pea and rice proteins deliver an ‘intermediate’ release between 3-4 hours, and a slower release from casein protein, which requires several hours to digest.


Boost absorption with enzymes

Researchers⁷ who studied ways to improve protein absorption found that digestive enzymes can offer benefits.

The study ⁷ found that it took 4 hours for amino acid levels to peak after consuming whey. Those who drank whey alone experienced a 30% increase in circulating amino acid levels compared to baseline in that time, while those who took 2.5g of enzymes with their whey saw amino acid levels rise 110% higher. Those who had double the enzyme dose (5g) faired even better, achieving 127% higher absorption.

However, it is important to note that various other factors can also impact protein bioavailability beyond the type of protein source and the use of digestive enzymes. Individual factors like age, health status, and digestive system function also materially impact protein absorption rates.


References

  1. Hoffman JR, Falvo MJ. Protein – Which is Best? J Sports Sci Med. 2004 Sep 1;3(3):118-30. PMID: 24482589; PMCID: PMC3905294.
  2. Moore DR, Soeters PB. The Biological Value of Protein. Nestle Nutr Inst Workshop Ser. 2015;82:39-51. doi: 10.1159/000382000. Epub 2015 Oct 20. PMID: 26545252.
  3. Basile EJ, Launico MV, Sheer AJ. Physiology, Nutrient Absorption. [Updated 2023 Oct 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK597379/.
  4. The digestion rate of protein is an independent regulating factor of postprandial protein retention. Am J Physiol Endocrinol Metab 280: E340–E348, 2001.
  5. Matsuoka R, Kurihara H, Nishijima N, Oda Y, Handa A. Egg White Hydrolysate Retains the Nutritional Value of Proteins and Is Quickly Absorbed in Rats. ScientificWorldJournal. 2019 Aug 27;2019:5475302. doi: 10.1155/2019/5475302. PMID: 31534442; PMCID: PMC6732637.
  6. Effect of Protein Blend vs. Whey Protein Ingestion on Muscle Protein Synthesis Following Resistance Exercise. Journal Nutrition. 2013 Apr; 143(4): 410–416.
  7. An open label study to determine the effects of an oral proteolytic enzyme on whey protein concentrate metabolism in healthy males. JISSN, 2008.