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Article: Casein vs Whey: What's the best source of protein for swimmers?

Casein vs Whey: What's the best source of protein for swimmers?

Casein vs Whey: What's the best source of protein for swimmers?

There's a lot of information out there about proteins and which are the best source of protein for swimmers. Here we break down the basics of two important proteins for swimmers and some considerations as you integrate whey and casein into your nutritional training program.

Whey and casein are both excellent sources of essential Amino acids (building blocks for proteins that cannot be produced by the body). They also score a 1.0 in the highest Protein Digestibility Corrected Amino Acid Score, a measure of protein quality based on Amino acid utilization after it is being digested. The biggest difference between these two proteins is the rate they are absorbed by the body.

What is whey?

Whey is the watery by-product of cheese production. This water portion of milk that is left over after the curds have separated is whey protein. It is concentrated and dried, which results in the popular powder form that most of us use in our diets. Whey also has high levels of leucine, a potent amino acid that stimulates protein synthesis (which promotes muscle building). Consuming repeated doses of whey allows for sustained high levels of blood amino acids and repeated bursts of protein synthesis that provide superior effects on muscle protein balance. We will get into why this is a good thing below. 

How does it work?

Whey protein is considered a “fast” protein. Fast refers to the amount of time it takes for whey protein to be fully metabolized. Shortly after ingestion, whey protein's solubility allows it to be absorbed from the stomach and into the small intestine. This results in a large and rapid spike of amino acid plasma levels (a fantastic medium that promotes muscle synthesis), however, this response is short-lived, lasting only a few hours after ingestion.

Why do I need it?

Muscle growth is dependent on the balance between protein synthesis and breakdown. If the synthesis of new muscle protein is greater than the breakdown of muscle protein, net gains in muscle mass are seen. So with whey protein, you are enabling your body to synthesize protein at a faster rate since this process only takes about 40 minutes for blood levels of amino acids and protein synthesis to reach a peak.

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What is casein?

Casein is considered a “slow” protein and is the most abundant protein in milk. It is relatively insoluble and tends to form structures called micelles that increase solubility in water. During the processing of milk, the casein peptides and micelle structure become denatured to form simpler structures. As a result, a gelatinous material is formed. This is the basis for why casein has a slower rate of digestion, and results in a slow, but steady release of amino acids into circulation.

How does casein work?

Casein’s superior long-lasting effect is due to a delayed gastric emptying and slower absorption rate from the gastrointestinal tract to the blood.

Why do I need it?

Casein has the ability to provide your bloodstream with a slow and steady flow of amino acids that could last for hours. According to studies by the Nutrition and Toxicology Research Institute Maastricht in the Netherlands, subjects who increased their casein intake had a higher metabolic rate while sleeping and a better overall fat balance. In other words, by taking casein you’ll be increasing your odds of keeping lean muscle and losing fat, which is important for swimmers who are trying to stay as strong and lean as possible.

Casein vs. Whey. Do I need both whey and casein?

In brief, yes! Since whey rapidly increases protein synthesis and casein blocks protein breakdown, a combination of both would be ideal. Some athletes mistakenly think that it would be best to just drink whey protein drinks all day to keep your system full of amino acids, but just having constantly high levels of amino acids doesn’t equate to protein synthesis. Studies show that supplementation with a mix of whey and casein proteins resulted in greater increases in lean muscle mass and muscle strength.

Because whey and casein have different but complementary effects, many athletes keep both types on hand and use them differently throughout the day. For example, whey in the morning and after workouts and casein before bed is a great supplement to your training diet. Or you can use the NutriBoost Shake, which has the ideal mix of both proteins to sustain the ideal proportion of whey and casein to give your nutritional program an edge.


  1. Protein - Which is best? – Journal of Sport Science and Medicine 
  2. Protein and Exercise – Journal of the International Society of Sports Nutrition

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