Whey protein is a milk-derived protein that is highly bioavailable, fast acting, and inexpensive, and it has many qualities that make it superior to most other protein sources, especially for the athlete. It also provides an easy way for athletes to meet their high protein needs. This article outlines the types of whey, their strengths and weaknesses, and many of the less well-known benefits of whey protein.
As far as protein quality goes, whey is top of the line. Various methods have been used to evaluate protein quality. The most well-known is biological value (BV). This is a measure of how much of the protein that is absorbed is retained for use. Egg protein, which was originally thought to have the highest bioavailability of any protein, is the standard reference with a bioavailability of 100. Whey protein concentrate has a bioavailability of 100 as well, compared to around 90 for milk and 70-80 for meat. Some protein hydrolysates and isolates may have higher biological value.
PDCAAS (protein digestibility-corrected amino acid score) is a more recent method of determining protein quality, and is used to determine percent daily value for protein on food labels. The PDCAAS is based on whether or not a protein meets the human amino acid requirements (hence, incomplete proteins have lower scores) as well as how digestible the protein is. The maximum PDCAAS is 1.00, and whey protein has a PDCAAS of .99-1.00.
Both of these methods have both strengths and weaknesses, but illustrate that whey is a very high quality protein. There are a number of other variables we can look at as well, which more effectively establish the unique properties of whey: protein synthesis, protein breakdown, and speed of digestion. Different proteins have a spectrum of effects in this regard, but follow a general pattern: There are "slow" and "fast" proteins, and fast proteins tend to significantly stimulate protein synthesis for a short period of time, while slow proteins (such as casein) stimulate protein synthesis to a much lesser extent but inhibit protein breakdown for a longer period of time. Being a fast acting protein, whey has the capability to stimulate protein synthesis at the most crucial times, such as during the workout period. In contrast, slower acting proteins like casein are ideal for fasting periods where inhibiting protein breakdown becomes more of an issue, such as before bed. For example, one study found that whey stimulated protein synthesis by 68% compared to 31% for casein, but casein resulted in a higher net leucine balance (a marker of protein synthesis and degradation) over a seven hour period (1).
In addition to being a fast acting protein, whey contains very high amounts of glutamine and branched chain amino acids (BCAAs) as well as other essential amino acids. Studies by Tipton et al. indicate that essential amino acids are the most important in supporting protein synthesis in the post-workout period (2).
Studies support the idea that whey protein exerts an anabolic response when taken before and after workouts. While exercising and in the following hours, protein breakdown and synthesis both increase drastically, and a readily available protein source is essential to changing the initially catabolic response from exercise into an anabolic one. In a rat study, glucose, milk protein, and alpha-lactalbumin (a milk product) enriched whey were compared when administered preworkout every day for five weeks. All three groups gained weight, but in the first two groups the weight was primarily from fat while in the whey group it was primarily lean body mass (3). A human study with 36 males also found that 1.2 g/kg of whey per day resulted in greater lean mass than with no supplement, with creatine and whey having additive effects (4).
Whey protein has many other benefits besides stimulation of protein synthesis and amino acid profile. One article refers to whey as "more than a source of protein," as it contains many beneficial growth factors, toxin-binding factors, antimicrobial peptides, probiotics, and immune regulatory factors (5), and the combination of these things has many unique properties that are absent from other protein sources (including casein). Indeed, whey is now being researched in the areas of immune support, cancer prevention, digestive tract health, hypertension, bone strength, metal chelation, liver support, and even the treatment of stress.
One of the most important biological activities whey has is the ability to increase levels of glutathione (GSH), the body's primary antioxidant (6). There are probably multiple mechanisms of action for this ability, the primary being that whey is high in cystine, the disulfide form of the amino acid cysteine, as well as other GSH precursors (7). Cysteine also helps remove toxic metals from the body, while the presence of other aminos in whey that compete for entry into the blood brain barrier may prevent the cysteine-metal complex from crossing the barrier and placing toxic metals in the brain, an effect that high doses of cysteine supplements have been implicated in (8). The GSH precursors in whey protect the stomach from damage (9), while the resulting elevation of GSH in various tissues from whey has a protective effect against cancer in these tissues (10).
Numerous other substances present in whey also have beneficial effects on health. Whey-derived growth factor decreases damage and increases repair to the intestine (11), beta-lacoglobulin and alpha-lactalbumin may aid in the prevention and treatment of hypertension (12), and milk basic protein, a fraction of whey protein, has been shown to increase bone formation in healthy men (13). Finally, the high amount of tryptophan in whey, especially when combined with alpha-lactalbumin, causes reduced stress and cortisol in stress-prone subjects when compared to casein (14). The dosage that is most commonly used for beneficial health effects is 45 g of whey protein per day.
Of course, the type of whey protein can change the biological activity. Whey protein concentrate (WPC) is at best 80-85% protein by weight, and contains undesirables such as lactose and fat. However, it is also the best way to ensure that you get all of the other beneficial components of whey – the more processed it is, the more likely it is that some of these components will be lost. On the other hand, the most processed form of whey, hydrolyzed whey ("predigested" with enzymes), yields superior nitrogen retention (15) and still possesses at least some antioxidative capacity if properly processed (16). CFM whey is the best source, as it contains both the protein and the active components, but once again this is assuming that it is properly processed. Ion-exchange whey may be more bioavailable but the ion exhange process destroys the other active fractions. All in all it comes down to how much money you want to pay, how much you trust the supplement company (Optimum 100% Whey has tested and meets label claims), and how important it is for you to avoid the extra lactose and fat. Because of the easy digestibility, hydrolyzed whey is probably superior in the workout period, but many people cannot tolerate the taste.
Because whey has benefits that other protein sources have to offer, but some other proteins (such as casein) have qualities that whey doesn't have, it can be concluded that a blend of proteins is best, and that different proteins are optimal during different times. Whey protein forms the cornerstone of any bodybuilder's regimen, and is a powerful tool for gaining muscle as well as improving general health.