Q: What is the difference between whey protein and casein? Does it matter which one I use as a protein source?

A:

Both whey and casein are complete protein sources containing all the essential amino acids. Either one can be used to satisfy your daily protein requirements. And although they are milk-based proteins, most of the lactose is removed during extraction so they shouldn’t pose much of a problem for the lactose intolerant. Just add them to water, juice, or whole foods for a power-packed meal.

If you really want to be scientific about your nutrition and optimize your results, however, the manner in which these two protein sources are used can make a difference in your physique. First let’s cover the basics.

Although whey and casein have similar amino acid profiles, there are inherent differences between the two. The important thing to know from a body sculpting perspective is that they digest at different speeds. Whey is a “fast-acting” protein, meaning it’s rapidly absorbed into circulation, generally within about an hour’s time. Casein, on the other hand, is a slow-acting protein. It “clumps up” when subjected to stomach acids, dramatically slowing down absorption. So how can you use this information?

Because it’s rapidly assimilated, whey is perfect as a pre- and/or post-workout protein source. It reaches your muscles quickly, thereby expediting repair. And since your muscles are primed for anabolism (growth) during and after a training session, virtually all the protein will be utilized for rebuilding with little wastage. In the pre-workout period, aim for about one-tenth of a gram of whey per pound of bodyweight (i.e., a woman weighing 120 pounds would need about 12 grams of whey) while post-workout the amount should be about one-quarter of a gram of protein per pound of bodyweight (the same 120-pound woman would need about 30 grams of whey).

Conversely, casein is better as a general protein source during “non-workout” periods, either as a meal replacement or simply to meet daily protein requirements. It is particularly good to take before bedtime. During sleep, your body becomes catabolic, breaking down muscle tissue for their amino acids. Since casein takes roughly three to four hours to be fully assimilated, it provides the body with a steady supply of aminos throughout much of the night, significantly limiting protein breakdown. This results in a higher net daily nitrogen balance, leading to better muscle retention.

It is important to understand, though, that taking whey and casein over and above your normal protein requirements won’t do any good from a muscle-building standpoint. Unfortunately, protein cannot be stored in your body for future use. When you consume more than what your body can handle (generally about one gram per pound of bodyweight a day), the rest will simply be excreted (or stored as fat, if your calories are in excess of what you expend).