Research Review: Fast vs. slow whey for protein synthesis

Whey protein is the most popular source of protein for athletes and bodybuilders. It has been shown to provide a number of benefits, including increased muscle growth, improved recovery time after exercise, and reduced muscle soreness.

The casein protein vs whey reddit is a research review that discusses the differences between fast and slow proteins.

Casein digests slowly, while whey protein digests rapidly. Researchers wanted to see whether rapid digestion or delayed digestion is better for protein synthesis and muscle growth in this experiment. What’s the bottom line? The greatest way to increase muscle protein synthesis is to eat quickly.

Protein powder is a must-have for anybody looking to bulk up. I’m sure some of you PN Coaching muscle-builders have huge paint-can-sized containers of protein powder as furnishings in your apartments. (Congratulations! Continue to eat!)

You’ll discover more brands, tastes, and kinds of protein than you can imagine at most supplement shops. Of course, most individuals choose a powder that they can stomach, since many products have an unpleasant flavor (may we suggest a SuperShake instead?) But, which one is the best?

What is the definition of protein powder?

For begin, protein powder is just dried protein that has been processed into a handy and portable form. (See All About Protein Powders for additional information.) These powders may be made from a wide variety of foods, including:

  • dairy products (whey and casein)
  • a hen (whole egg or egg white)
  • soy
  • hemp
  • pea
  • beef, too
  • etc.

In 2004, dairy-based proteins accounted for about three-quarters of all protein in sports supplements. The remainder was mostly made up of soy proteins. [1] Plant-based protein powders have grown increasingly popular in recent years. Dairy proteins like whey and casein, on the other hand, still make up the majority of protein supplements on the market.

The most popular type of dairy-based protein powder is whey protein powder, which is a liquid by-product of cheese production. Casein, on the other hand, is derived from the solid portion of skim milk after it has been acidified (like lemon juice). Casein is the curd component of milk that forms when it curdles.

Dairy proteins (as well as egg protein) are called complete proteins because they contain adequate quantities of all necessary amino acids. A few plant proteins, such as hemp, are likewise complete, although their total protein content is lower.

Casein versus whey

Whey and casein have been a staple for bodybuilders for years. Each protein has unique characteristics. But which is better?  Well, just like comparing an economy car and a sports car, deciding which protein is better depends on the purpose of the protein.

In terms of similarity, both proteins are complete and have the same Protein Digestibility Corrected Amino Acid Scores (PCDAAs; 1.00) [2]. So, in order to figure out which is superior, we’ll have to delve a little further.

When it comes to differences, whey protein has more leucine, while casein contains more glutamine (Figure 1). Whey is also considerably more rapidly absorbed than casein.


Isolated soy protein (ISP), whey protein (WP), and casein concentrations of isoleucine, leucine, valine, glutamine, and arginine. The grams per 100 grams of protein are used to calculate the values. It was adapted from (2).

In the synthesis of muscle protein, leucine and glutamine are important.

The mammalian target of rapamycin (mTOR) pathway, which is activated by leucine, stimulates skeletal muscle protein synthesis via a sequence of molecular biology interactions that behave like dominoes. Whey is an excellent option for increasing muscle growth because it contains more leucine, which is a crucial amino acid for stimulating protein synthesis.

Glutamine is also important in muscle protein synthesis. After exercise, glutamine is depleted in blood plasma and muscle. More muscle glutamine is directly correlated to higher muscle protein synthesis. Glutamine supplementation leads to more growth hormone, which has anabolic affects on muscle.

Rates of absorption

Another distinction between whey and casein protein is how quickly and for how long the protein is absorbed.

The rate of protein absorption is calculated by measuring blood amino acids. Whey protein consumption causes blood amino acid levels to rise in less than an hour, peaking at just under 90 minutes. Casein takes slower to raise blood amino acids, but the effects persist longer, lasting over 300 minutes [3].

Table 1: Summary of Whey vs. Glutamate

Protein that is completeYesYes
Leucine is abundant in this dish.YesNo
Glutamate is abundant.NoYes
Rate of absorptionFastSlow
Blood amino acid levels have been high for a long time.ShortLong

Clearly, comparing whey and casein is difficult. Different amino acids, absorption rates, and immune system impacts are all factors to consider.

How can you know what’s important? One strategy is to maintain all other circumstances the same and then alter one item.

The same protein (constant) was utilized in this study, but the time it took for participants to eat it was changed (change one thing). Or, as I like to refer to it, the chugging vs. sipping test.

Question for investigation

The topic of today’s study is whether the pace of intake — and therefore the rate of absorption — affects the benefits of protein supplementation.

DW West, NA Burd, VG Coffey, SK Baker, LM Burke, LM Hawley, DR Moore, T Stellingwerff, SM Phillips After resistance exercise, rapid aminoacidemia boosts myofibrillar protein synthesis and anabolic intramuscular signaling responses. 2011 Sep;94(3):795-803. Am J Clin Nutr. 2011 Sep;94(3):795-803. The article was published on July 27, 2011, and it was epub on the same day.


On two occasions, eight moderately active young men consumed 25 grams of whey protein after doing leg extension strength testing (10 rep max).

  • Trial 1: The guys downed the whole 25 grams in one sitting.
  • Trial 2: The men drank 2.5 grams of casein 10 times over 200 minutes (with a shot of whey every 20 minutes), simulating the gradual yet lengthy absorption of casein.

Blood samples were used to determine the levels of amino acids and leucine in the blood. Isotope labeling, a biological method, was used to quantify muscle protein synthesis (fractional synthesis rate; FSR).

Muscle biopsies were also used to assess the levels of particular proteins involved in controlling muscle protein production. Muscle from the outer quadriceps is sampled using a biopsy needle the size of a pen barrel (vastus lateralis).


Either chugging or shooting a total of 25 grams of whey protein both increased essential amino acids and leucine in the blood (Figure 2a & b).

When compared to serial shooting (pulse), bolus produced a greater peak level of essential amino acids and leucine, but after 5 hours, everything appears to balance out. Based on the area under the curve (AUC), which is a method of looking at levels throughout time rather than simply the peak, chugging and firing had the same impact on overall levels, as seen in Figure 2.


Figure 2 – Blood concentrations of a) essential amino acids and b) leucine after consuming whey protein all at once (BOLUS; 25 grams) or after more than 200 minutes (PULSE; 2.5 grams X 10 drinks every 20 minutes). DW West et al., 2011. (Figure 2).

We actually want to know what happens to protein synthesis in the muscle, as fascinating as blood leucine levels are (aka myofibrillar protein synthesis). The curve of protein production is shown in Figure 3. As can be shown, consuming all of the whey protein at once (bolus) boosted protein synthesis more than consuming the same quantity of whey over a 3-hour period (pulse).


Figure 3: Average myofibrillar protein synthesis rate (myofibrillar FSR) after fasting (fasted), BOLUS (1X 25 grams), or PULSE (2.5 grams X 10 drinks every 20 minutes) after exercise. DW West et al., 2011. (Figure 4).


More muscle protein synthesis is caused by high peak levels of blood leucine and amino acids than by muted but prolonged elevated levels of blood leucine and amino acids. So, how does this affect you?

If you want to develop muscle, consume a fast-digesting protein drink (with at least 25 grams of protein) within 15 minutes after doing out. You may drink a second fast-digesting protein drink 2 or 3 hours after the first if you truly want to try something new. It’s possible that a second drink after blood amino acids have returned to normal may induce a second surge in blood leucine, resulting in increased muscle protein synthesis.

[Of course, this study doesn’t directly suggest that casein or any other slow protein has no value.  After all, casein wasn’t even used in this study.  Rather, the researchers tried to mimic casein’s effects by slowing down the absorption of the whey protein.  In fact, slow digestion may be an asset during other times of the day.  However, after exercise, slow proteins might not be best.]

If you can’t digest dairy, replace it with lean proteins from whole foods like eggs, shellfish, or lean meats, and keep your post-workout fat consumption low while increasing your carb intake to accelerate absorption. Have some lean protein an hour or two before your workout to ensure that amino acids are already floating about. If at all feasible, take your largest protein meal of the day as soon as possible after a strenuous workout. Include some BCAAs (branched-chain amino acids) in your workout.

In conclusion

Drinking 25 grams of fast-digesting whey protein all at once, just after exercise, boosts muscle protein synthesis more than drinking 25 grams of whey protein three hours later.


To see the information sources mentioned in this article, go here.

  1. Sports Nutrition and Weight Loss Report 2007-2008 from the National Business Journal. Boulder, CO: New Hope Natural Media, January 2008. Nutrition Business Journal. Boulder, CO: New Hope Natural Media, January 2008.
  2. The reason for using protein mixes in sports nutrition, Paul GL. 2009 Aug;28 Suppl:464S-472S. J Am Coll Nutr. 2009 Aug;28 Suppl:464S-472S. Review.
  3. Slow and rapid dietary proteins influence postprandial protein accretion differentially, according to Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, and Beaufrère B. 1997 Dec 23;94(26):14930-5. Proc Natl Acad Sci U S A. 1997 Dec 23;94(26):14930-5.

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The is chicken fast digesting protein is a research review that discusses the benefits of fast and slow whey proteins.

Frequently Asked Questions

Is fast or slow digesting protein better?

Fast digesting protein is better for people who have a busy schedule and dont have time to eat often.

Is whey optimal for protein synthesis?

Whey is a milk protein that is often used in the diet for muscle growth. It is also an excellent source of protein, which makes it very useful for the synthesis of new proteins and muscle tissue.

Which Whey protein is best for fast muscle growth?

The best protein for fast muscle growth is a whey protein blend.

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