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Whey is a big buzzword in the active world. Not just for bodybuilders, whey is a key ingredient of many muscle recovery drinks catering towards all kinds of athletes. But what exactly is whey and why is it so common in these products? What about its relatively unknown counterpart, casein? Is that good too? This article should help answer these questions and others that you may be curious about.

Whey and casein proteins are both derived from mammalian milk. Casein is predominant, constituting about 80% of protein found in milk. Whey makes up the remaining 20% of milk protein. Casein is commonly used to produce cheese, and whey is the natural byproduct of that process.

Protein structure

The difference in the molecular structures of whey and casein proteins accounts for the dissimilarities in how they act within the human body. Whey protein is simple, consisting of only amino acids in a globular structure, and is relatively soluble. Casein, in contrast, lacks a true tertiary structure, taking a form resembling a denatured globular protein. This results in the hydrophobic portions of the amino acid building blocks to be exposed, making the overall protein insoluble in water. Because of this, casein molecules aggregate into colloids when in solution.

Because both whey and casein are derived from the same source, their amino acid profiles are similar. Whey does contain greater amounts of glutamine and leucine, however both proteins have the amino acid content necessary to meet normal dietary needs.

Rate of metabolism

Whey is a fast acting protein with amino acid levels in the blood peaking 20-30 minutes post consumption, and fully metabolized within the hour. Casein is absorbed at a much slower rate, peaking in the blood 3-4 hours after it is consumed, with peak levels much lower than those experienced with whey.

Casein takes much longer to absorb than whey because of its property of coagulating when coming into contact with certain stomach enzymes, in a process very similar to the curdling of milk. This coagulation slows the digestion of all other contents in the stomach, which is the cause of milk making the drinker feeling full.

Protein synthesis

Because casein is slow to digest, it has an anti-catabolic, or muscle breakdown preventing, effect, keeping amino acids available in circulation over time, in order to prevent the breakdown of muscle tissue. Whey’s quick influx of blood amino acids provides muscle tissues with materials necessary to stimulate muscle synthesis and growth, making it an anabolic, or muscle building, agent.

Recommendations

For athletes, whey is an excellent choice to deliver a quick and abundant supply of protein to the muscles, especially post exercise when a strong and immediate influx of protein is necessary to start the recovery process. It would be advisable to avoid sources of protein that include casein, however, as its coagulating effect will slow the absorption of all else consumed, delaying the delivery of protein and other nutrients needed for proper muscle recovery. For those who are looking for a protein supplement during times of inactivity, such as between workouts or before sleep, casein would be the optimal selection in order to slow the catabolic breakdown of muscle and to give the athlete a good, full feeling.

References

Goeff HD & Hill AR. 1993. Chemistry and physics. In Y.H. Hui (ed.), Dairy Science and Technology Handbook Vol. 1: Principles and Properties, 1-82. VCH Publishers, New York.

Mahe S, Roos N, Benamouzig R, Davin L, Luengo C, Gagnon L, Gausserges N, Rautureau J & Tome D. 1996. Gastrojejunal kinetics and the digestion of [15N]beta-lactoglobulin and casein in humans: the influence of the nature ad quantity of the protein. American Journal of Clinical Nutrition, 63: 546-552.

Walstra P & Jenness R. 1984. Dairy Chemistry and Physics. John Wiley and Sons, New York.

Wong NP, Jenness R, Keeney M & Marth EH (eds.). 1988. Fundamentals of Dairy Chemistry, 3^rd edit. Von Nostrand Reinhold, Yew York.