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Protein, whether we’re talking about the protein that makes up your own tissues, or that supplied by food, consists of amino acids linked together in chains. Amino acids are the principle means by which we get nitrogen –an essential element in your survival.
Building bigger muscles is about balance –protein balance. If your body makes more muscle protein than it breaks down (i.e., a positive protein balance) your muscles will increase in size and strength with time. Conversely, if you make less muscle protein than you break down (i.e., a negative protein balance), your muscles will tend to get weaker and smaller.
Scientists refer to ‘building up’ (synthetic) processes as ‘anabolism’ or ‘anabolic’; ‘catabolism’, or ‘catabolic’ processes, in contrast, involve breaking down tissue structures. Thus, a positive protein balance indicates an anabolic state.
A Positive Protein Balance is Essential to Building Bigger Muscles
Since protein contains nitrogen, we can estimate your protein balance by measuring your nitrogen balance. Technically speaking, however, the two should not be considered equal. In any case, a positive nitrogen balance is generally taken as a sign of an anabolic state with an overall gain (retention) of nitrogen for the day, whereas a negative nitrogen balance indicates a catabolic state.
Another, arguably more accurate, way to estimate your protein balance is by measuring your body’s balance of a particular amino acid, such as leucine. A positive leucine balance indicates protein anabolism. Or, at least, a positive leucine balance reflects a state (i.e., increased availability of leucine inside your muscle cells) that supports protein anabolism. Conversely, a negative leucine balance suggests protein catabolism (‘breaking down’). Simply stated, a positive leucine balance is ‘good’; a negative leucine balance, ‘bad’, for the purpose of building bigger muscles.
Maintaining Muscle Protein Balance
You don’t eat all the time; there are gaps in your protein intake, such as in between meals and while you sleep.
So how does your body preserve its protein balance? How does it keep your ‘Protein Economy’ (the total amount of protein in your body) from shrinking --and your muscles alongside-- in the face of fluctuating intakes of dietary protein?
Your body maintains its protein balance largely by adjusting tissue protein breakdown according to how much protein you feed it (for review see Garlick et al., 1999).
In between meals (e.g., overnight), you lose tissue (e.g., muscle) protein, but after a protein-containing meal, you recoup what you lost through a decrease in protein breakdown. The production, or synthesis, of tissue protein often stays about the same after a protein-containing meal (Melville et al., 1989; Price et al., 1994; Garlick et al., 1999), yet because protein breakdown is reduced, the result is a net increase (gain) in protein such that balance is achieved. You don’t get bigger, but you don’t shrink, either.
In order to actually make your muscles bigger and stronger, you’ve got to work on both sides of the protein balance equation. However, the stimulation of muscle protein synthesis is by far the most important half of the muscle-building equation. This cannot be emphasized enough. Indeed, the stimulation of muscle protein synthesis is the means by which resistance exercise makes muscles grow (Barr and Esser, 1999); it’s also how some of the most powerful muscle-building hormones (e.g., testosterone, growth hormone, insulin-like growth factor-1) work their magic.
Whey vs. Casein
Now we’re prepared to discuss protein supplements. Whey and casein are the two major proteins in milk. Whey is frequently touted as the highest quality protein available for the bodybuilder or similarly-focused individual. Yet these claims appear to reflect a vast misinterpretation of the available scientific literature on the matter.
Absorption: Faster is Not Better!
When you eat a serving of whey protein, its digestion in your gut results in a very rapid, but short-lived, surge of amino acids into your bloodstream (Boirie et al., 1997). Casein, by comparison, yields a slower, more sustained release of amino acids (Boirie et al., 1997). Importantly, casein’s slower absorption profile seems to better promote a positive protein balance (Boirie et al., 1997) –an essential requirement for building bigger muscles.
Recall from above that one way of estimating your protein balance is by measuring your body’s balance of a particular amino acid, such as leucine. A positive leucine balance indicates a state (i.e., increased availability of leucine inside your muscle cells) that supports protein anabolism. Conversely, a negative leucine balance indicates conditions favoring protein catabolism.
Ironically, whey protein marketers have been known to cite the Boirie study (Boirie et al., 1997) as evidence with which to support whey’s ‘superiority’ as a muscle-building protein. Contrary to what their ads and articles (‘advertorials’) imply, however, Boirie et al. found that casein –not whey— produced the most positive leucine balance when fed to healthy young humans. In fact, whey actually produced a negative leucine balance.
The negative leucine balance associated with eating whey protein resulted from a greater loss of leucine, through its irreversible ‘burning’, or oxidation. Furthermore, when the subjects in the Boirie et al. study ate whey protein, more urea was formed than when they ate casein. Urea is a waste product of amino acid breakdown. Nitrogen from amino acid breakdown is irreversibly transferred to urea. Since urea cannot be reused, it represents a loss of nitrogen.
To sum it up, at least under the conditions of this study, casein demonstrated superior potential for promoting a positive protein balance as compared to whey – not the other way around. But even so, will this difference translate into faster gains in muscle size for you? Maybe. Maybe not. The answer must be determined by long-term, controlled clinical trials.
Whey’s Frequently Touted ‘Virtue’ Is Actually Its Downfall
Again, whey is often said to be superior to casein because of its ability to deliver amino acids into your bloodstream rapidly. Yet this is not a virtue; rather, it’s a weakness.
When it comes to amino acid absorption, haste makes waste. The rate at which amino acids are broken down, or catabolized, is directly related to the level they achieve in the bloodstream (Reeds et al., 1992). The faster the amino acids provided by the protein you eat exit your gut and enter your bloodstream, and the higher the blood levels they attain, the more they get wasted.
The higher your blood levels of the amino acid leucine, for instance, the greater its rate of catabolism. Eating whey protein drives blood leucine levels very high (Boirie et al., 1997). Not surprisingly, this results in a corresponding loss of leucine through catabolism (Boirie et al., 1997). And as indicated above, whey generates more urea –the waste product of amino acid breakdown— than casein.
Barnyards, Hair and Feathers
There’s another longstanding issue we need to clear up. To do so, let’s go visit the animals in the barnyard. A barnyard filled with cows, sheep, dogs, rats, cats, chickens.
What do all these creatures have in common? And what the heck has this got to do with bodybuilding and whey protein supplements?
Plenty, in fact. To answer the first question, unlike you and me, all of above barnyard creatures are covered in either hair or feathers. Hair and feathers are made of the protein known as keratin, which is rich in the sulfur-containing amino acid, cysteine (found in keratin in its oxidized form, cystine).
Cysteine can be produced in animals from another sulfur-containing amino acid, methionine. Since whey has more sulfur-containing amino acids than casein, hair- or feather-covered animals require less whey than casein to achieve protein balance. But this advantage will clearly does not apply to humans, a relatively hairless and featherless species, as the Boirie et al. study would seem to agree.
Nevertheless, studies performed over a half-century ago on hair- or feather-covered animals which demonstrated the ‘superiority’ of whey over casein, have been used as marketing ‘support’ by companies selling whey protein supplements.
Back in 1947, Tomarelli and Bernhart demonstrated that feeding whey protein (hydrolyzed -lactalbumin, more specifically) to rats produced greater protein retention than did casein (e.g., Tomarelli and Bernhart, 1947). The rats required about 70% more casein nitrogen than whey nitrogen per day to maintain nitrogen balance. These results are consistent with a number of similar studies performed around this time. The trouble is that these studies, too, were performed on animals covered either in hair or feathers –rats, dogs, and chickens, for instance. Thus, these data are applicable to barnyard animals, but not to humans.
Methionine is an essential sulfur-containing amino acid. As I noted earlier, it can be used by your body to synthesize cysteine (as in the production of keratin). Rats, which were commonly used in early studies to determine the frequently-quoted “Biological Value” (BV) of various dietary proteins, have a methionine requirement that is around 50% greater than you or I (Sarwar et al., 1989). This contributes to the lower BV numbers reported for dietary proteins containing relatively less methionine when such proteins are fed to rats, as compared to humans (Bricker and Mitchell, 1947).
Johnson et al. (1946) relate: “In the case of the human experiments, then, it would be concluded that the methionine requirement is lower, and is not a limiting factor in the attainment of nitrogen excretion in these experiments, or that the requirement is met by the body protein breakdown plus any dietary protein….Since the addition of further methionine did not reduce the nitrogen excretion on the low protein diet, it can be concluded that no more methionine is required under these circumstances than that represented by the entire sulfur excretion, or 1.4 gm methionine per day for our average subject….the present experiments suggest that the human body is not limited in its ability to conserve nitrogen by the need to meet a methionine requirement.”
Cox et al. (1946) clarify even further: “comparison of the nitrogen retention of a casein hydrolysate with and without added methionine in rats, dogs and man has clearly shown a striking species difference. The addition of methionine increased the rate of growth in rats and the magnitude of nitrogen retention in dogs. In man, however, it was without effect on nitrogen retention…An explanation for this difference does not seem difficult, based on the fact that the rat and dog are covered with hair, and that man is not. Since hair contains large amounts of cystine, it is reasonable to suppose that the requirement for this amino acid (or methionine) is considerably greater than that of man…The generally recognized nutritive difference between casein [lower in cystine] and lactalbumin [higher in cystine] is valid for the rat and for the dog, but not for man.”
CONCLUSION
As the above evidence hopefully makes clear, the claim that whey is superior to casein for building muscle is simply not valid.
The study performed by Boirie et al. (1997) found evidence to suggest that casein is superior to whey for promoting a positive protein balance. But that doesn’t necessarily mean it will build muscle any better than whey, or a chicken breast meat, for that matter.
Protein supplement ads and articles frequently cite Biological Value (BV) numbers (e.g., 104 and sometimes even higher) for whey as evidence for its superiority; however, these BV values were derived from studies on hair- and feather-covered animals that require more of the sulfur-containing amino acids that whey is rich in. These results do NOT apply to humans.
