Geschatte leestijd: 5 minutenWhey protein is one of the most popular, if not the most popular, supplements for strength training and muscle growth. Whey plays an important role in the diet of strength athletes for good reasons. However, more attention should be given to slower forms of protein, specifically casein. The actual point of this story is that casein is underrated. Given the popularity of whey, however, I expect this title to attract more attention, because “woe to anyone who comes between a bodybuilder and his whey.”
Muscle growth results from muscle synthesis and breakdown
Muscle growth results from muscle synthesis and muscle breakdown. Muscle growth is caused by the production of protein in the muscles from amino acids transported through the blood (protein synthesis). Muscle breakdown, on the other hand, is caused by the breakdown of this protein into individual amino acids. The entire process of protein synthesis and breakdown is called protein metabolism. Muscle growth can only occur when protein synthesis is greater than protein breakdown in the muscles (1). This is called a “positive protein balance” (1).
We train to stimulate muscle growth by heavily loading them and then provide nutrition so that a) the body has the resources to grow (anabolic phase) and b) there is no need for muscle breakdown to provide the body with energy (catabolic phase). Immediately after training, the need for protein is high because the amino acids in the protein are needed for muscle recovery and growth. Due to the intensity of training, hormones are also released such as insulin, growth hormone, testosterone, and IGF-1. These signal the body to enter an anabolic phase. These effects of training typically last 24 to 48 hours, and the “interaction between protein metabolism and the meals eaten” determine the effect of nutrition on hypertrophy/muscle growth (1).
“Fast” and “slow” proteins
Whey is highly valued because the amino acids from whey are absorbed into the bloodstream very quickly and are available to the muscles compared to other (natural) types of protein (2). The faster the amino acids are available, the faster protein synthesis can start and the shorter the period of amino acid deficiency that could lead to breakdown.
Casein is called “slow protein” because the speed of amino acid absorption from it is much slower (2).
In practice, you often see people using whey after training when the need for fast protein is high. Casein is often used before sleep to provide the muscles with protein for (ideally) the 8-hour fasting period for as long as possible. Then whey is often taken in the morning with the thought that the casein did not suffice in the last hours of the night, and thus amino acids need to be pumped into the bloodstream as soon as possible upon waking.
Casein less anabolic but anti-catabolic for a long time
All of that sounds very logical. However, French researchers wondered if the different absorption speeds of two types of protein also have different effects on protein metabolism (2,3). In two different studies, they looked at the absorption rates of amino acids from whey and casein.
In the first study from 1997, they looked at absorption when whey and casein were taken separately (2). They “labeled” the amino acid leucine in both proteins for this purpose. This allows them to precisely see when and to what extent this amino acid enters the bloodstream. In the graph on the right, you can see results plotted against time, whey is represented by the triangle and casein by the black circle. It is clear that whey causes a higher increase in the amount of leucine half an hour to 3 hours after ingestion. Casein still rises in the first half hour but then remains stable. Where whey dips below the point of casein after 3 hours and barely causes an increase an hour later, casein actually rises slightly and continues to increase the amount of leucine in the blood even after 7 hours.
The researchers also looked at the amount of “endogenous” leucine in the blood and the rate at which this appears (endogenous leucine rate of appearance). That is, the amount of leucine in the blood that did not come from the ingested protein and thus originates from muscles that have broken down protein for this purpose. This is an indication of muscle breakdown. It is visible that both whey and casein limit breakdown after ingestion. However, with whey, this lasts only about 90 minutes after which breakdown starts to increase again and is soon back at the old point. Casein, on the other hand, begins to have a greater limiting effect on breakdown and then lowers it until 6 hours after ingestion, after which it slowly rises back to the old point.
As a result, whey has a greater anabolic effect due to faster availability and a higher rise in amino acids, while casein limits breakdown more. The French researchers concluded that casein limits protein breakdown in the muscles by 34%, whereas whey does not provide significant limitation of breakdown. Whey, on the other hand, increases protein synthesis (thus growth) by 68%, whereas casein is lower at 31%. Over a period of seven hours after ingestion, casein according to the French has a greater added value (3):
“Most importantly, postprandial leucine oxidation was significantly higher after ingestion of whey proteins than after ingestion of casein despite identical leucine intakes.
Therefore, the postprandial leucine balance, an index of protein deposition, was better with casein than with whey. Taken together, our results suggested that, in young adults, “slow” proteins (e.g., casein) fare better than “fast” proteins (e.g., whey) with respect to postprandial protein gain.”Y. Boirie, Université Clermont Auvergne
The above results apply when whey and casein are taken separately. In a later study, they looked at what happened when they were taken together (4). Even when taken together, casein had a longer-lasting effect, although the differences shortly after ingestion were smaller than when taken separately.
“Here, with proteins coingested, we show that phenylalanine appearance into the hepatic vein (and therefore, systemic circulation very soon after) is similar between proteins initially rather than higher, as expected from the work in which proteins were ingested separately. However, importantly, consistent with the previous whole body study, the Cas phenylalanine outflow into circulation was sustained, whereas WP phenylalanine outflow from the liver moved back toward baseline sooner. Therefore, the present study demonstrates that Cas leads to more sustained systemic amino acid delivery and, therefore, more sustained delivery to the skeletal muscle.”
M. Soop, Mayo Clinic
Conclusion
This doesn’t mean you should only buy casein from now on. After all, the studies have shown that both contribute in different ways. For this reason, I advocate for the combined intake of both proteins to maximize the different benefits they offer.
Furthermore, I have only looked at two types of protein here. If you were to extrapolate the conclusions of these studies to other, even faster forms of protein such as hydrolysates, you might suspect that these have an even greater anabolic effect, but at the same time do less (long) to limit breakdown. For this reason, I use hydrolysates around training (e.g., Pepto Pro, whey hydrolysate) to provide the necessary amino acids as quickly as possible. An hour later, I then take a mix of whey and casein (such as Premium Protein) to extend the length of the anabolic effect and limit breakdown.
There is still insufficient research to have insight into a comparison of all different types of protein, how they work together, and at what time and in what amounts each type of protein has the greatest added value. With this article, I at least wanted to make it clear that it is not a simple story of: “The faster, the better”.
References
- Tipton KD, Wolfe RR.Exercise, protein metabolism, and muscle growth.Int J Sport Nutr Exerc Metab. 2001 Mar;11(1):109-32.
- YVES BOIRIE, MARTIAL DANGIN, PIERRE GACHON, MARIE-PAULE VASSON, JEAN-LOUIS MAUBOIS, AND BERNARD BEAUFRERE. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc. Natl. Acad. Sci. USA. Vol. 94, pp. 14930–14935, December 1997. Physiology
- Dangin M, Boirie Y, Garcia-Rodenas C, Gachon P, Fauquant J, Callier P, Ballèvre O, Beaufrère B. 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.
- Soop M, Nehra V, Henderson GC, Boirie Y, Ford GC, Nair KS. Coingestion of whey protein and casein in a mixed meal: demonstration of a more sustained anabolic effect of casein.Am J Physiol Endocrinol Metab. 2012 Jul 1;303(1):E152-62. doi: 10.1152/ajpendo.00106.2012. Epub 2012 May 8.
