© 1999

Certainly one of the most widely utilized dietary tactics among strength-trained athletes is the consumption of a high-protein diet. For instance, it is not uncommon for elite bodybuilders to consume 400-500 g of protein per day. They do so claiming they have found this results in optimal gains in muscle hypertrophy. What these individuals do not realize is that their strategy may be less than optimal. In fact, it may actually prove self-defeating.

Several studies of resistance-trained individuals have demonstrated a significant increase in nitrogen retention when supraphysiological amounts of protein were administered. A positive nitrogen balance is generally thought to reflect an increase in lean body mass, particularly skeletal muscle when a strength-training stimulus is present. Thus, the evidence supports consumption of extra protein in these athletes, at least superficially. However, in many instances, what the researchers measured was not the effect of a high-protein diet per se, but rather the investigators measured the effect of an acute increase in protein ingestion. In other words, most studies collected data during a change in the diet. Many of such studies would have likely found that if the observation period would have been of greater duration, the positive effects of the high protein diets would have been diminished as the body adapted to the diet. The decrease in the efficiency of protein utilization with chronic ingestion of a high-protein diet partly explains why nitrogen balance studies of resistance trainees have shown a broad range of ceilings for "optimal" protein intake since some subjects entered the studies having habitually consumed a normal protein diet while others had been consuming a high-protein diet.

This dietary dilemma is further complicated by the widely advocated practice of frequent protein consumption every three hours or so. It is conceivable that this strategy may also decrease the body’s adeptness at handling periods of less protein consumption. For example, this practice could cause one to enter into a catabolic state during sleep when one goes for many hours without food. Perhaps not surprisingly, some athletes do go so far as to wake in the night so that they may fulfill their need to feed.

The body’s adaptability to varying quantities of dietary protein is not an unusual physiological capability. The concept of conservation versus elimination with respect to nutrients is relatively ubiquitous throughout the body. When we consume too much of a particular nutrient, the body becomes more efficient at ridding the body of that substance. This is usually accomplished through a decrease in absorption from the gastrointestinal tract and/or an increase in metabolism and elimination of the nutrient. Conversely, when a nutrient’s demand surpasses a nutrient’s supply, the body makes attempts to conserve that nutrient.

In a correlational study, my colleagues and I reviewed the findings of nine nitrogen balance studies of resistance-trained individuals in which protein intake was manipulated (manuscript submitted for publication). Among our calculations, we found that net protein utilization (NPU), a measure of the efficiency of dietary protein utilization, decreased by almost 70% when compared to that of the average American. There are a number of factors that could contribute to this observed decrease in efficiency of utilization, but nevertheless the subjects were generally very inefficient with regard to nitrogen consumed as protein versus nitrogen retained. NPU would have likely decreased even further over a longer period of exposure to increased dietary protein.

Our recent findings lend support to the notion that chronic consumption of a high-protein diet leads to a dependency on such a diet. In our previous example of elite bodybuilders’ notable protein consumption, it is possible that the athletes themselves create a protein dependency. Their bodies, accustomed to copious dietary protein, squander their protein resources so that progressively more protein is needed to result in optimal protein accretion in the form of muscle hypertrophy. It is obvious that one cannot increase one’s protein intake indefinitely. So what can be done to resolve this issue?

A possible solution to this protein paradox may rest within a concept known as protein cycling. Protein cycling has been written about previously but, as of this writing, has never been experimentally tested. The underlying premise of protein cycling is consuming supraphysiological amounts of protein when the body has been primed to utilize the protein with maximum efficiency. This is hypothetically accomplished by very gradually tapering off protein ingestion to modest levels over several weeks followed by abruptly increasing protein intake. After several additional weeks when the body has adapted to the high-protein diet by increasing amino acid degradation, the process is repeated. Additionally, the variable of meal frequency could be manipulated to further increase the body’s efficiency. For example, the frequency of protein feedings could be reduced to increase the body’s efficiency of protein usage in preparation for the high-protein phase of the cycle.

It could be years before data on protein cycling are collected and the research is replicated. But, it only makes sense to attempt to harness the adaptive mechanisms that have ensured our survival for millions of years. It is always prudent to work with the body, not against it.

Part II of this article will describe a possible framework for the practical application of protein cycling.

Dr. Greg Bradley-Popovich holds dual master's degrees in Exercise Physiology and Human Nutrition from West Virginia University as well as a doctorate in Physical Therapy from Creighton University. He is the Director of Clinical Research at Northwest Spine Management, Rehabilitation, and Sports Conditioning in Portland, Oregon.

Back to Library Main Page