Dear BLOG readers, dear PEAK customers,
In Part 1 of my 2-part article, I dealt with the distinction between fast proteins and slow proteins, the gastric retention time and the absorption speed of various proteins. The conclusion is that there is indeed a distinction between slow and fast proteins. However, the terms are often misinterpreted.
Slow and fast proteins - a myth? Part 1
Today I would like to take the research from Part 1 as a basis to discuss whether there are advantages or perhaps even disadvantages to be expected from a more or less rapid absorption rate.
Differences in the time of absorption?
In principle, it can be assumed that the amino acid concentration after the intake of the corresponding protein is the same at any time of day. However, what changes particularly when ingested after training is the flow of blood to the muscle cells. According to studies, this is 30 - 100 % higher than in a resting state and therefore also has a positive influence on protein synthesis via this mechanism.
Conclusion
Increased blood flow to the muscles is particularly noticeable after training.
We will need this information again later...
Resorption rate and protein turnover
We know from Part 1 that there are fast and slow proteins, a fact that is certainly a relief for many. What we do not yet know, however, is the extent to which these differences affect the body's own protein turnover, i.e. the build-up and breakdown processes of proteins in our body.
Study
To this end, Boirie, Y., Dangin, M., Gachon, P. et. al investigated the influence of a 30 g portion of casein and the same amount of whey protein on the amino acid concentration in the blood in a time sequence. In order to distinguish whether the measured amino acids originated from the respective meal or from endogenous protein turnover, radioactive tracers were attached to the amino acid leucine of the supplied protein. The test subjects were 16 young, healthy men with an average age of 24 years and an average BMI of 21.
As a result, Figure 1 shows the overall increase in leucine, how the endogenous protein turn-over behaves in parallel and how the intake of the two proteins ultimately affected the amount of leucine.
As expected, the whey protein triggers a rapid and stronger increase in leucine, thus strongly inhibiting endogenous protein breakdown in the short term and ultimately generating a high, rapid increase in leucine overall, which reaches its PEAK around 60 minutes after ingestion. After a short time, a downward trend in blood amino acid levels can be observed again.
The casein also produced an increased amount of leucine after about 60 minutes, but not to the same extent as the whey protein. In contrast to whey protein, endogenous protein breakdown was inhibited over a much longer period of time, which ultimately resulted in 34% less protein breakdown over the measurement period.
Similar effects on protein breakdown as with casein were not observed with whey protein, but protein synthesis increased more quickly in the short term.
Conclusion
Whey protein causes a rapid increase in the absolute amount of amino acids, but quickly falls again. In contrast to casein, it increases protein synthesis quickly, but has no significant effect on protein breakdown, which is why it can be assumed that the combination of both protein variants can generally be regarded as the most potent choice.
Fast or slow proteins - the better choice?
A general question that now arises on our topic is whether the speed of digestion should actually be a decision criterion when buying a protein supplement or whether it is solely the amino acid constellation of the respective protein that determines the positive effects.
In order to find out, Yves Boirie, Bernard Beaufrere and colleagues have brought some extremely interesting study results to light. In the course of their investigations, they made the following findings, some of which we are already familiar with:
- Whey protein is absorbed faster than micellar casein
- The amino acids from whey protein (especially BCAA and in particular leucine) are used to a much greater extent to provide energy
- Micellar casein can generally, but especially after training, prevent the breakdown of muscle protein
- Micellar casein is superior to whey protein in terms of utilization
With regard to the effects of digestion speed, the researchers found that this appears to be even more important than the amino acid profile of the respective protein. For further studies, they used different proteins, but standardized the amino acid compositions and nitrogen content to determine the pure effect of absorption speed.
In a comparison of the effects of 30g casein and a mixture of 30g free amino acids, the uptake of the amino acid mixture resulted in a faster uptake and an increase in protein synthesis. However, neither contributed to improved leucine balance or increased protein storage, but resulted in increased oxidation of amino acids, similar to the rate seen with standardized whey protein. Protein degradation was only slightly inhibited with the amino acid mixture, while the intake of slow casein significantly inhibited degradation for over seven hours.
In a further study, a single dose of a protein was compared with multiple doses of 2.5 g every 20 minutes. As known from the chapter on gastric retention time from part 1, it was to be expected that the protein drink with the complete 30 g would be digested and utilized more quickly. As in the previous studies, some of its amino acids were used for energy production, while protein breakdown was not prevented. The distribution over several hours ensures a constantly increased amino acid concentration of four to five hours, although this was at a much lower level than could be demonstrated with the single dose. The small doses reduced protein degradation but did not significantly affect protein synthesis. The researchers came to the conclusion that the extent of the change in amino acid levels and the length of the increase were decisive factors. Quickly available proteins (such as whey protein) are better suited directly after training, as the muscles absorb protein more effectively here (as already mentioned above). Slowly available protein ensures improved absorption at all other times of the day and protects body tissue better against breakdown.
Conclusion
With the exception of after training, slower digesting proteins are the better alternative when it comes to building, protecting and maintaining muscle.
Net yield as a disadvantage of fast-digesting proteins?
Now that a fast digestion rate has been shown to be advantageous, at least for certain times of the day, it is necessary to give the whole thing a brief summary. Julius Oben et al published an interesting study in the Journal of International Society of Sports Nutrition in 2008, in which they apparently raised justified doubts about the net yield of rapidly available proteins. They investigated the effects of a single dose of 50 g whey protein concentrate on the actual absorption yield, once with and once without the additional intake of a digestive enzyme complex, in young healthy and non-overweight subjects. The CG (control group) received a placebo, TG-A-5 received 5 g of an enzyme complex of proteases, TG-A-2.5 received 2.5 g of the same enzyme complex.
The results showed significant differences in the amount of amino acids in the blood. The different effects of the 2.5 or 5 g supplement on the net intake are of secondary importance at this point. Of decisive importance, however, is the reduced uptake of amino acids that was observed, triggered by a transit time that was too short and apparently overtaxed endogenous proteases. Of 50g of protein supplied, only 15g were actually absorbed into the blood, and this when using a whey protein concentrate, which we found to be nowhere near as fast as hydrolysates or isolates in terms of digestion speed.
Conclusion
It is possible that fast proteins are a little too fast and overtax our proteases, our body's protein cleavers, which can result in a reduced net yield of amino acids in the blood. The addition of exogenous enzymes to fast proteins should definitely be reconsidered from this point of view.
Summary
After reviewing all the data, studies and facts, it can be concluded that different absorption rates of proteins are not a myth and are definitely important when it comes to using the right protein at the right time. Overall, slowly available proteins have the edge for both muscle building and muscle maintenance, regardless of the amino acid constellation. It is only after training that you benefit from consuming a rapidly available protein, as this ensures a rapid increase in amino acid concentration and drives protein synthesis. The question of the actual net yield and the efficiency of protein-splitting digestive enzymes in connection with the intake of fast proteins remains open.
With best regards
Holger Gugg
Sources
Boirie, Y., Dangin, M., Gachon, P. et. al. "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 M1, 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.
