NW Spine - Library

 

Protein Permutations: A Review with New Insights into an Age-old Question --Part I

 

by Greg E. Bradley-Popovich, DPT, MSEP, MS, CSCS

 

© 2000

Originally published in Anabolic

 

INTRODUCTION

What's the problem?

In case you are relatively new to resistance training, it has long been debated among nutrition and exercise scientists as to whether active individuals or athletes require more dietary protein per unit body weight than those values espoused by the various government agencies for normal sedentary subjects. This ongoing debate is between one school of thought, which believes that athletes and other active individuals do not require more protein than sedentary individuals, versus another that believes those engaged in physical activity have special needs. Increases in protein loss in athletes have been shown to occur through several means including, but not limited to, the following: source of energy, collagen repair, collagen hypertrophy, myofiber repair, myofiber hypertrophy, protein hidrosis (losses in sweat), and proteinuria.

 

When examining the protein needs of physically active individuals, one must further divide this diverse segment of the population into categories of subjects in search of specific training effects. As training techniques and goals vary, so does nutriture (Reimers, 1994). Athletes can generally be grouped into three broad categories: those individuals seeking aerobic conditioning, those seeking anaerobic conditioning, and those seeking a combination of these two forms of conditioning.

 

Of the aforementioned categories, the focus herein will be towards predominantly anaerobically-trained persons. Anaerobic athletes are athletes who participate in bursts of activity that last a short duration, generally less than two minutes. If you're reading this magazine, chances are you're an anaerobic athlete. Two outstanding and highly visible examples of athletes who seek strength and muscle gains are weight lifters and bodybuilders. Other examples of anaerobic athletes include sprinters, shot putters, and gymnasts.

Of the various anaerobic athletes, most of the data regarding protein metabolism and protein requirements have been collected on weight lifters and bodybuilders. (Lucky for us!) Because much of this article will focus primarily on these two groups, let's take a moment to define them. Weight lifters desire to increase strength as much as possible and view muscle hypertrophy as a means of increasing strength. In contrast, bodybuilders are not preoccupied with strength gains per se, but with the accretion of muscle mass associated with strength development. In other words, for the bodybuilder, strength development is the means, not the end. Yet, both weight lifters and bodybuilders ultimately depend upon the hypertrophy of muscle to one extent or another. Additionally, bodybuilders strive to minimize body fat stores more so than weight lifters.

By no means is muscle hypertrophy desirable only in certain athletic populations. Rehabilitation patients, the active elderly, and general fitness enthusiasts may all qualify as athletes, though not in the traditional sense of the competitive context. Certainly non-competitive "athletes" comprise a far greater proportion of the population than competitive or elite athletes. Therefore, this article will include studies performed on a variety of participants from neophytes to professionals, all undergoing some form of resistance exercise, often to induce skeletal muscle hypertrophy.

How are protein needs increased with resistance exercise?

The previously mentioned metabolic fates of protein as a result of exercise are general routes that apply to virtually all athletes, though to varying degrees depending upon the nature of the training. For example, under certain conditions, some protein will be oxidized for energy, as is commonly depicted in the glucose-alanine cycle, which uses the branched-chain amino acids, especially leucine, to provide an amine group for the formation of the amino acid alanine. The alanine, in turn, is carried from the muscle to the liver where it is used to form glucose to be consumed by the working muscles or the central nervous system. In addition to their role in the glucose-alanine cycle, the dietary essential branched-chain amino acids isoleucine, leucine, and valine are the primary amino acids oxidized under exercise stimuli, because the working skeletal muscles can oxidize them intramuscularly (Lemon, 1987). Other amino acids as well as the branched-chain amino acids can be degraded to Krebs Cycle intermediates in the liver to provide energy during exercise. Despite the detailed understanding of the biochemical pathways involved in transforming protein into energy-yielding substances, the overall loss of protein through such degradation for energy is agreed to contribute a very minor role in increasing the protein needs of anaerobic athletes (Lemon, 1995).

The tissue damage that occurs as a result of the high-intensity muscle contractions common to anaerobic athletes includes insults to the connective and muscle tissues. Connective tissue, primarily made of the protein collagen, has been shown to increase proportionally with muscle hypertrophy (MacDougall, 1986). Thus, the absolute amount of connective tissue in an anaerobic athlete increases with training. Muscle hypertrophy occurs by two means: increased size of myofibrils in a muscle fiber and possibly an increased number of myofibrils in a muscle fiber (MacDougall, 1986). These increases occur via the assimilation and incorporation of additional protein. Thus, the healing and hypertrophy resulting from strength training may be largely responsible for any increase in protein need.

Also, additional protein is lost in urine, a condition known as proteinuria. It appears to be positively related to exercise intensity. Proteinuria may be caused by a decreased reabsorption of amino acids in the kidney tubules during intense exercise. This avenue would be negligible, accounting for no more than 3 grams of protein per day (Poortmans, 1985).

Protein losses in sweat, protein hidrosis, also occur as a result of exercise. Both amino acids and proteins have been found in sweat. Approximately 1 gram of protein is lost in each liter of sweat. Again, these losses are relatively minor and training in a very warm environment would result in a loss of less than 3 g N/day (Celejowa and Homa, 1970; Consolazio, Johnson, Nelson, Dramise, and Skala, 1975; Lemon, Tarnoplosky, MacDougall and Atkinson, 1992; Walberg, Leedy, Sturgill, Hinkle, Ritchey, and Sebolt, 1988).

 

It appears that muscular growth accounts for the majority of additional protein needed by resistance-trained individuals. Additional dietary protein, then, mainly serves the needs of the growth mechanism.

 

Because the largest dry weight of muscle consists of protein, many athletes and researchers have suspected that increasing dietary protein intake above normal values may facilitate muscle hypertrophy. However, the wet weight of muscle is mostly water (Oser, 1965).

It is most appropriate that weight lifters and bodybuilders have primarily served as the anaerobic athletes on which many protein studies have been conducted. The lore and common "wisdom" promulgated in muscle magazines and gyms everywhere place protein high on a pedestal. Protein is generally regarded as an essential and almost mystical ingredient in achieving optimal progress in these sports.

What are some of the arguments surrounding protein and resistance training?

At least two interesting arguments regarding protein requirements of resistance-trained individuals have been published in popular body building literature. These arguments arise not from physiology or nutritional biochemistry, but from mathematics. First, many bodybuilding journalists have emphasized that conventional nutrient allowances such as the Recommended Dietary Allowances establish a suggested protein intake that will be sufficient for approximately 98 percent of the population (National Academy of Sciences National Research Council, 1989). Therefore, they logically conclude that 2 percent of the population will not be covered by the recommended nutrient allowance. To quantify this conclusion, the bodybuilding authorities delineate that just 2 percent of the population of the United States (roughly 260 million people) is equal to more than 5 million people. They argue, therefore, that many bodybuilders and other athletes under strenuous training are likely to be part of this minority for whom the conventional allowance is inadequate.

On the other hand, some bodybuilding authorities point out that muscle growth is a relatively slow process and if muscle accretion alone is quantified on a daily basis, the need for copious amounts of protein above the conventional allowances are discredited. For example, if an individual were to increase his muscle mass by an impressive 20 pounds (9.09 kg) in one year, that would amount to about 2,000 grams of assimilated net muscle protein. (Each pound of muscle at 454 g is about 22 percent protein, and .22 X 454 = 99.8 g protein.) Averaged out over the course of a year, the 2,000 g would amount to only an additional 5.5 g of protein above daily maintenance requirements. This viewpoint is supported by Durnin who estimated this figure to be 7 g/day (1978). In contrast, Brotherhood (1984) cites research which indicates that the estimated value for lean body mass gains may exceed 50 g/day during aggressive muscle building programs.

It cannot be assumed that protein assimilation in muscle tissue occurs with 100 percent efficiency, as is the underlying assumption with the former argument which suggests a surplus of just 5.5 g of protein per day. There is no guarantee that all of the additional protein, once absorbed, will arrive at its intended destination (Di Pasquale, 1997, p. 73). This is because the amino acids in sufficient amounts must not only be made available during muscular growth, but must be available at the time a particular amino acid is being incorporated into a translated protein. Thus, because protein synthesis is continuous, it is a hit-or-miss situation in regards to the supplying of a particular amino acid at the correct time (Di Pasquale, 1997, p. 82). This imperfect efficiency accounts, at least partially, for the apparent mathematical discrepancies that have persisted for years: why it appears to require a lot of protein to build a comparatively small amount of muscle.

If you feel a little confused and think all these arguments sound pretty convincing, don't feel badly. I was so confused by it that I decided to devote two years of graduate school to this very subject!

Look for the next installment in this series, in which I'll review numerous scientific trials that have examined the effects of supraphysiological protein ingestion during resistance training. Is there any scientific evidence to support the axiom of eating one gram of protein per pound of body weight, or is it merely popular opinion? Perhaps more importantly, I'll reveal some information that is hot off the press!

 

About the Author

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.

 

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