Dear BLOG readers, Dear PEAK customers,
There are several approaches to differentiating between proteins. First of all, there are animal and plant proteins. They are differentiated by their origin.
The second distinction separates proteins with a high insulin index from those with only a minor influence on insulin secretion.
The third distinction is biological value, which refers to the ability to convert dietary protein into the body's own protein. A final distinction separates proteins into fast and slow representatives and thus refers to blood availability, i.e. the time a protein needs until the amino acids split from it are available in the blood.
A number of nutrition systems are based on this theory of fast proteins and slow proteins and sometimes use this approach to recommend when to consume certain types of protein.
Since I am one of those people who like to check unwritten laws for their origin, today I will look at the question of whether the theory of fast and slow proteins is true and what conclusions can be drawn from it to help optimize your nutrition plan in terms of protein intake.
Stomach retention time and absorption rate
Stomach retention time
When it comes to absorption, i.e. the absorption of amino acids from the intestine into the blood, you actually have to start researching a little further back, namely where a not insignificant part of protein digestion takes place, namely in the stomach. Different foods are "held" there for different lengths of time until the stomach porter releases them in doses into the intestine. In technical terms, this is known as the gastric retention time and refers to the length of time a food spends in the stomach. It depends on several factors and is usually between one and six hours.
Solid or less chewed food stays in the stomach longer than liquids. In addition to the consistency, the osmolarity, i.e. the particle concentration, is also involved in the gastric retention time. This is particularly important for liquids and especially for the absorption of monosaccharides, as these irritate the osmoreceptors of the duodenum in different ways. The composition of nutrients also influences how long they remain in the stomach. Fats and carbohydrates in particular ensure a longer retention time. This is due to their influence on osmo- and chemoreceptors in the digestive tract. Ultimately, a high energy density also ensures a longer gastric retention time. However, it is important to know that with high-calorie meals, more energy is released into the small intestine per unit of time than with a low energy density.
This brings us to the crux of the issue of gastric retention time in connection with protein intake, which is repeatedly misinterpreted.
Conclusion
Depending on the properties of a food, it remains in the stomach for a longer or shorter period of time before the nutrients are released into the small intestine.
Rate of absorption
Although a long gastric retention time means that a food takes a long time to leave the stomach completely, it does not mean that this time is also required for the first pre-digested nutrients to leave the stomach. This is not the case, as the stomach releases fully processed nutrients to the small intestine in measured doses.
Absorption of whey protein
When whey protein (whey) is ingested, the first amino acids are already present in the amino acid pool of the blood 30 minutes after ingestion. The maximum level (peak) is reached after about 45 to 120 minutes. After about three hours, the concentration has normalized again.
Not all whey is the same
As whey protein is available in several different forms, it stands to reason that there are also differences in terms of absorption. Quasi pre-digested proteins, such as whey hydrolisate, cause blood amino acid levels to rise faster than whey concentrates.
Kalmann et al. assume that the first amino acids from protein hydrolisates arrive in the blood as early as 15 minutes after ingestion, but that this increased concentration falls back to the initial level after 90 minutes.
The absorption rate here would be the same as that of free amino acids. High-quality whey isolates are also characterized by an absorption speed that can almost compete with free amino acids.
The absorption of whey concentrates will take a little longer, as this dosage form lacks short-chain peptides and therefore requires a little more digestion.
Interesting
Soy protein isolate is known to have an absorption time that is almost equal to that of whey protein.
Casein takes its time
Casein is known to remain in the stomach for up to 7 hours. However, even with casein, a moderate amount of amino acids can be detected in the blood just one hour after ingestion, which then lasts for several hours.
Incidentally, this property does not apply to casein hydrolisate, which is why the time-released effect typical of casein cannot be assumed here.
Medium-fast
Soy protein and egg protein are often described in the literature as "medium-fast" proteins and that is exactly what they are. The gastric retention time of both is around 2 - 3 hours, i.e. it takes a little longer for a large amount of amino acids to be found in the blood.
Conclusion
In general, it takes quite a short time for the first amino acids from each protein source to be present in the blood. The big difference is the quantity per time unit and the time-released effect, i.e. the time unit in which an increased concentration of amino acids is present.
Summary
The theory of fast and slow proteins also proves itself in practice. While hydrolysates are generally the front runners in terms of absorption thanks to the short amino acid chains, it can be assumed that a larger quantity of amino acids from whey protein and also soy protein in its form as an isolate will be in the blood significantly faster than those from egg protein, soy protein concentrate and casein. Anyone who bases their calculations purely on the time they remain in the stomach is unfortunately on the wrong track.
With best regards
Holger Gugg
Sources
Boirie, Y., Dangin, M., Gachon, P. et. ali. "Slow and fast dietary proteins differently modulate postprandial protein accretion". Proc Natl Acad Sci U S A. Dec 23, 1997; 94(26): 14930-14935
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC25140/
https://www.spektrum.de/lexikon/ernaehrung/magenverweildauer/5520
D. Kalman et. al. Journal of the Int. Soc. of Sports Nutrition, July 2007
NBJ's Sports Nutrition and Weight Loss Report 2007-2008. Nutrition Business Journal. Boulder CO. New Hope Natural Media, January 2008.
Paul GL. The rationale for consuming protein blends in sports nutrition. J Am Coll Nutr. 2009 Aug;28 Suppl:464S-472S. Review.
Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrère B. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A. 1997 Dec 23;94(26):14930-5.
Dangin M, Boirie Y, Garcia-Rodenas C, Gachon P, Fauquant J, Callier P, Ballèvre O, Beaufrère B (2001). The digestion rate of protein is an independent regulating factor of postprandial protein retention. Am J Physiol Endocrinol Metab. 2001 Feb;280(2):E340-8.
