Anabolic Protein Limits

An unwritten rule of bodybuilding nutrition is that you should limit protein to no more than 30 grams per meal. So if a 200-pound bodybuilder should ideally get 1.7 grams of protein per kilogram (2.2 pounds) of bodyweight, that amounts to a suggested daily protein intake of 153 grams. In reality, most bodybuilders who weigh 200 pounds get considerably more than that. The recommendation is based on research that monitored protein use and absorption in a weight-training population. Despite that, you hear and read about champion bodybuilders who take in 300 grams or more protein a day.

Many dietitians and other health professionals who aren’t as well-versed in nutrition as their academic backgrounds would indicate espouse the idea that eating a large amount of protein can be problematic or even hazardous to health. They warn that it stresses the liver and kidneys, which at first glance seems to be true, as the liver and kidneys are the primary organs that metabolize protein in the body. Even so, normal liver and kidney functions are more than sufficient to handle the nitrogen-based waste products that result from eating a huge amount of protein. Having diseased kidneys or liver may require some changes in protein intake, but that doesn’t apply to an otherwise healthy population.

Other so-called expert claim that excess protein can make you fat, since a gram of protein does contain four calories and since too many calories eaten from any source can eventually wind up as bodyfat. Here again, however, is an example of scientific ignorance, perhaps duplicity. In active people the fate of excess protein is not storage but rather oxidation, mainly in the liver.

Again, the question arises: Is there an actual limit to how much protein you should eat if you’re trying to build muscle? Although the 30-gram rule has been around for decades, its source is not clear. Recent studies seem to confirm that there is indeed a limit to how much protein you can use at one time. For example, an intake of only six grams of essential amino acids maximizes muscle protein synthesis after weight training. Other studies narrow it even further, suggesting that just one essential amino acid—leucine—is the key to effective muscle protein synthesis after weight training.

Another theory is that getting excess protein spurs the synthesis of a major blood protein called albumin. Basically, the albumin is thought to act as a storage vehicle for protein, to be used when required for muscle and whole-body protein synthesis. Amino acids stored with albumin are protected from oxidation.

Until recently, no one had bothered to test the notion that 30 grams of protein or less is about all the body can handle after weight training. A new study tackled that issue in particular. Six healthy young men, average age 22, on five separate occasions reported to a lab, where they did intense leg exercise. After training, the men received drinks containing zero, five, 10, 20 or 40 grams of whole-egg powder. The researchers measured protein synthesis and oxidation over a four-hour period after the training ended by tracing tagged leucine.

They also monitored factors involved in muscle protein synthesis that are affected by amino acid intake, particularly the branched-chain amino acids, such as leucine. The factors become activated when phosphate groups are attached to them; however, in this study they weren’t affected by any amount of protein intake. The authors suggest that the exercise itself may have maximally stimulated the factors, which would obscure the effect produced by amino acids.

The study did find that both muscle protein and serum albumin synthesis were maximally stimulated with protein intakes under 20 grams at one sitting. Eating more than 20 grams of protein at a time results in increased protein oxidation with no further increase in muscle protein synthesis. The 20 grams contain 8.6 grams of essential amino acids, which is about the same amount that has proved effective in boosting muscle protein synthesis following weight training. Maximal protein synthesis at rest requires only 10 grams of protein per meal.

As for the lack of muscle-protein-synthesis-factor stimulation, adding carbohydrate to the protein would likely have favored more stimulation due to a greater insulin release. The authors note, however, that the exercise-induced increase in essential amino acid delivery into muscle results in upgraded muscle protein synthesis after weight training.

While some people advocate taking supplemental amino acids to spark muscle protein synthesis, in reality, having a constantly high level of aminos in the blood makes muscle resistant to protein synthesis. The excess amino acids are simply oxidized. According to the authors of this study, maximal protein synthesis can be achieved with 20 grams of protein per meal, eaten five to six times daily. Any more than that results in oxidation of the excess protein, with no further increase in muscle protein. In short, the excess protein is just wasted.

The authors also warn that eating huge amounts or protein regularly causes the body to oxidize less of it. That may actually result in a protein deficit, although I doubt whether it’s likely with most bodybuilders.

What is certain is that many bodybuilders are eating much more protein than they need for building muscle. Those 300-to-600-gram daily intakes that you hear about may not be causing health problems, but they aren’t helping to build muscle or strength, either.

I contacted one of the authors of the new study. Stuart M. Phillips, Ph.D., is an associate professor of kinesiology at McMaster University in Hamilton, Ontario, Canada. He’s published many articles about sports nutrition and muscle physiology in numerous professional journals. Phillips said that the recommendation of 1.7 grams of protein per kilogram of bodyweight is based on old, imprecise examinations of nitrogen balance. In contrast, his study measured actual muscle protein synthesis, a far more reliable method of determining protein use in relation to exercise. He notes, “The bottom line is that nobody has any idea how much protein you need to consume to maximize muscle growth, but based on our work, we see it as being much lower than anyone has previously speculated. This makes a lot of sense, since the rate of muscle growth is so slow in even the biggest guy that it can’t be much more protein, if any.”

Moore, D.R., et al. (2009). Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr. In press.