Protein: recent research and debate

By Nathan Payne

Editor’s Note: In the November 2009 print issue of The Dance Current, our “Healthy Dancer” column focussed on the body’s need for and use of protein. A discussion ensued in our letters to the editor in December/January 2009/10, which inspired writer Nathan Payne to develop a longer article on the topic.

More Research Leads to More Questions
The conventional nutritional wisdom in the area of protein use and classification of amino acids has changed. In the 1930s and 1950s Rose and colleagues performed a series of nitrogen balance studies on volunteers. The volunteers were fed diets deficient in one or more amino acids and as each amino acid was removed from the diet a corresponding deficiency would be observed in the body. It was only when the amino acid was re-introduced into the diet that the deficiency was reversed (Rose 1955).

More...
New understandings of protein such as biological use, individual variability and the dose-response relationship (i.e., what quantity of amino acid “x” reduces risk of deficiency), can only be refined by the development of controlled clinical trials.

Adjustments to an individual’s requirements for dietary protein consumption and use of amino acids can be impacted by a number of variables including but not limited to the intensity level and type of physical activity performed, biological differences, physiological and pathophysiological states (e.g., trauma and catabolic disease), protein quality and digestibility, and energy balance (i.e., meeting the functional needs of the body during rest and active states). For example, a sixty-two kilogram person who is incorporating resistance training, like weight-bearing physical activity, and endurance training, would require approximately 100 grams of protein or 1.6 grams of protein per kilogram of body weight per day. For the average Canadian, this level of protein would not be required to maintain a healthy lifestyle, and consuming the Recommended Daily Allowance (RDA) of 0.8 grams of protein per kilogram of body weight per day would be sufficient.

Earlier examinations of protein and training also discovered that training intensity, restricting calories through diet and following food plans that decrease the levels of carbohydrate and fat, could all decrease the efficiency of protein use in the body. These results would in turn alter the dietary protein recommendations for some athletes (Tarnopolsky et al. 1988).

Rather than generating conclusive evidence, the volume of research conducted in this area has raised many unresolved questions in nutrition science.

Measuring Nitrogen Balance to Determine Protein Requirements
The body’s principle uses of protein are energy and repair of muscle following exercise. Of the several approaches used by researchers to evaluate protein use, the most common is the nitrogen balance method. Nitrogen is required by the body to form proteins, hormones, neurotransmitters and other molecules related to the immune system. Nitrogen must be obtained in the diet through amino acids (components of proteins). One criterion to determine an individual’s protein requirement is the maintenance of a positive or zero level of nitrogen. However, nitrogen measurements can be impacted by a number of confounding variables. The results from research focussing on nitrogen balance data with respect to context, methodology and test subjects used, have subtle nuances that need to be compared with other research.

Do highly active individuals have greater protein requirements?
The Food and Nutrition Board (FNB) of the United States Institute of Medicine report on the evidence of additional protein needs cites studies published in 1992 and 1995 that conclude additional protein is not required for highly active individuals. This report differs from the combined position of the American College of Sports Medicine (ACSM), American Dietetic Association (ADA) and the Dietitians of Canada (DC) committee (2006 and 2009) as well as others. In their own study, Venderley and Campbell suggest that the protein needs of well-trained endurance and strength athletes are higher than that of sedentary persons (Venderley and Campbell 2006). These authors further note that the position of the ACSM, ADA and DC committee on higher protein recommendations were specifically for highly trained, elite athletes, and that otherwise their assessment is consistent with findings of the FNB, which suggests that there is little scientific support for increasing dietary protein recommendations for recreational or non-elite athletes. In the context of dance, this last statement would beg the question: Is a dancer a “recreational” or “non-elite athlete”, or does a dancer’s level of training equal that of other highly trained athletes?

The suggested range of 1.6 to 1.8 grams of protein per kilogram of body weight per day and greater for individuals pursuing high-level strength training, depending on intensity and duration of the strength exercise, has consistent support based on several studies (Campbell et al. 2007; Wilson et al. 2006; Tarnopolsky et al. 1992; Lemon et al. 1992). Similar results are found in studies focussed on endurance exercise and this may be due to the body’s use of protein for energy, or the fact that some proteins used in the studies are of lower quality compared to others (Phillips 2006). In a recent “Globe and Mail” article, Phillips is quoted as advocating a “middle path” between the low protein requirements suggested by research studies and the higher requirements advocated by many coaches and athletes (Hutchinson 2009). When it comes to wading through the results of these studies, the devil is in the details and you will likely draw your own conclusions.

So, where do dancers fit in?
Back to the earlier question of whether a dancer is a recreational or elite athlete, most of these publications classify the study participants as active or sedentary, or athletes who are training recreationally or professionally. One thing is clear: an RDA of 0.8 grams of protein per kilogram of body weight per day does not apply to everyone, especially dancers at different stages of training. Perhaps we should come back to consider how these studies define a recreational athlete. When examining individuals’ protein requirements, Tarnopolsky characterized a recreational athlete as someone participating in activity such as jogging four times per week at forty-five percent maximum oxygen consumption for one hour. This is a very different physiological scenario from a top sport athlete who may be training and competing at intensities of sixty to eighty-five percent of their maximum oxygen consumption for eight to forty hours per week (Tarnopolsky 2004). VO2 max, a measure of aerobic potential or the maximum amount of oxygen used during intense/maximal exercise, may not necessarily be the best method of testing performance. A dancer will differ in training impulse and peripheral adaptations compared to a cyclist or runner. In other words, VO2 max values collected from a study participant riding a stationary bike may not be transferable to a dancer or other athletes. So where does a dancer fit in this scheme? I would argue that many dancers, during their initial stages of training, as well as throughout their careers, would fall somewhere within the range of physical activity presented in the Tarnopolsky article.

Protein requirements are also impacted by intensity, duration and type of exercise (Lemon 2000). Recent intervention studies have examined the importance of consuming protein with carbohydrate during exercise (Beelen et al. 2008). Campbell and colleagues also noted that strength/power exercise is thought to increase protein requirements even more than endurance exercise, particularly during the initial stages of training and if there is a sharp increase in the intensity and frequency of training (Campbell 2007). It would be reasonable to surmise from this data that a dancer would have increased demand for protein as well. For example, in rehearsals involving more strength movements, including jumping and lifts, the body will require greater amounts of protein and energy to sustain the activity and for recovery (repair to damaged muscle tissues).

In evaluating this research, however, one should keep in mind that a proper food plan, which includes adequate carbohydrates, will have a sparing effect on amino acid oxidation and protein balance (Elwyn et al. 1978). In other words, protein will not be the first choice for fuelling the body if one consumes a sufficient amount of carbohydrates. Therefore, it is generally recommended to include snacks composed of a mixture of both protein and carbohydrate, especially when training over an extended period of time.

Protein Intake and Renal Function
There is a widely held belief that additional protein, beyond the recommended daily intake for the general population, could stress the kidneys. Most of the studies that observed a negative impact on renal function were conducted on animals and patients with co-existing renal disease so an extension of those findings to healthy individuals is inappropriate (Martin et al. 2005). A report of a joint World Health Organization/Food and Agriculture Organization/United Nations University Expert Consultation published in 2007 suggests that a high intake of protein in healthy subjects does not lead to a deterioration of kidney function. This same report concludes that, with respect to safe upper limits for adults, “an intake of twice the recommended intake … is likely safe given that it equates to intakes of physically active individuals consuming average mixed diets who would otherwise be identified as having healthy lifestyles.” This statement is supported by the most recent review published in the “Journal of the International Society of Sports Nutrition”, which summarizes research results concerning renal function in athletes and finds the data to be inconsistent, especially when looking beyond the population of chronically diseased people (Lowery and Devia 2009).

Classifying and Combining Proteins
In terms of the relevance of essential (“indispensable”) amino acids and non-essential (“dispensable”) amino acids, researcher Alan Jackson suggested reclassifying amino acids into four categories based on the ability or inability of the body to synthesize all or part of the amino acid (Jackson 1983). The traditional classification of essential or indispensable amino acids (IAAs) and non-essential amino acids is a little less rigid today due to certain physiological circumstances that make particular amino acids “conditionally” essential. Laidlaw and Kopple further modified this classification based on research indicating that humans synthesize amino acids differently in healthy and diseased states (Laidlaw and Kopple 1987). So in certain circumstances, when an amino acid is no longer synthesized in the body, it must be consumed through diet in sufficient quantities to avoid any deficiencies.

The classic nutritional theory of protein combining within one meal in vegetarian diets has also been refined over the years. The position of the ADA and DC is that one does not have to consume complementary proteins at one meal, and that consuming a variety of foods throughout the day will also ensure minimum levels of protein are being met (Mangels et al. 2003). However, I would also argue that the concept of strategically consuming a variety of grains, pulses and other meat alternatives throughout the day for various eating habits (vegetarian or other) is not common knowledge for most people and is even more relevant today. If an individual does not follow the basic tenet of consuming fruits and vegetables, it would be reasonable to assume that they may also stray away from whole food sources of protein found in pulses and grains. More specifically, they may not appreciate the variability in quality and quantity of plant and animal proteins.

This knowledge is especially important for those deriving a majority of their protein from plant sources in order to support an active lifestyle or during bouts of training. A modification in one’s food plan is particularly important if one decides to completely eliminate particular animal proteins. The latest data collected by a recent Ipsos Reid poll was well publicized. Unfortunately, it found that 23% of all Canadians surveyed did not consume any vegetables or fruit in their diet and 91% of younger adult men and women did not eat the recommended daily amount. As noted by Venderley and Campbell: “A vegetarian diet can provide all essential and non-essential amino acids from plant foods alone if a variety of foods are consumed throughout the day and energy intake is adequate (Venderley and Campbell 2006).”

The practice of food combining throughout the day is important because the quality of amino acids is not the same in all foods. The Protein Digestibility Corrected Amino Acid Score has been adopted as the preferred method for the measurement of protein value in human nutrition (Schaafsma 2000). For example, if a dancer follows a diet composed mostly of cereal grains, which are often deficient in the amino acid lysine, either another complementary food item, such as quinoa, various other seeds and legumes, or a strategic supplement, such as a dose of spirulina or other, if one is vegan, is recommended.

The biological systems addressed here are complex. Dietary needs are diverse and individuals living either active or sedentary lifestyles may need to adjust their food plan in relation to the general recommendations. There is considerable evidence that the dietary protein needs of a dancer are different than that of the average person. Therefore, it is reasonable to assume the RDA may not be sufficient for everyone. Not all foods are created equally, and so consuming a variety of foods, with extra attention during periods of increased physical activity and training, will ensure unique dietary needs are being met.

References

American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada. (2009). “Joint position statement: Nutrition and athletic performance”. Medicine & Science in Sports & Exercise, 41(3), 709-731.

Beelen, M., Koopman, R., Gijsen, A. P., Vandereyt, H., Kies, A. K., Kuipers, H., et al. (2008). “Protein coingestion stimulates muscle protein synthesis during resistance-type exercise”. American Journal of Physiology, Endocrinology and Metabolism, 295(1), E70.

Campbell, B., Kreider, R. B., Ziegenfuss, T., La Bounty, P., Roberts, M., Burke, D., et al. (2007). “International society of sports nutrition position stand: Protein and exercise”. Journal of the International Society of Sports Nutrition, 4, 8.

Elwyn, D. H., Gump, F. E., Lles, M., Long, C. L., & Kinney, J. M. (1978). “Protein and energy sparing of glucose added in hypocaloric amounts to peripheral infusions of amino acids”. Metabolism: Clinical and Experimental, 27(3), 325-331.

Food and Nutrition Board (FNB) of the United States Institute of Medicine. (2005). “Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients).” A Report of the Panel on Macronutrients, Subcommittees on Upper Reference Levels of Nutrients and Interpretation and uses of Dietary Reference Intakes, and the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes.

Hutchinson, A. (2009, May 8). “Easy on the protein shakes big guy”. Globe and Mail, pp. L.3. Retrieved from http://www.theglobeandmail.com/life/do-i-need-to-quaff-protein-powders-to-gain-muscle/article1139578/

Joint World Health Organization/Food and Agriculture Organization/United Nations University Expert Consultation. (2007). Protein and amino acid requirements in human nutrition No. 935. Switzerland: WHO Press.

Jackson, A. A. (1983). “Amino acids: Essential and non-essential”. Lancet, 1(8332), 1034-1037.

Laidlaw, S. A., & Kopple, J. D. (1987). “Newer concepts of the indispensable amino acids”. American Journal of Clinical Nutrition, 46(4), 593.

Lemon, P. W., Tarnopolsky, M. A., MacDougall, J. D., & Atkinson, S. A. (1992). “Protein requirements and muscle mass/strength changes during intensive training in novice bodybuilders”. Journal of Applied Physiology, 73(2), 767.

Lemon, P. W. R. (1996). “Is increased dietary protein necessary or beneficial for individuals with a physically active lifestyle?” Nutrition Reviews, 54(4), 169-175.

Lemon, P. W. R. (2000). “Beyond the zone: Protein needs of active individuals”. Journal of the American College of Nutrition, 19(Supplement 5), 513.

Lowery, L. M., & Devia, L. (2009). “Dietary protein safety and resistance exercise: What do we really know?” Journal of the International Society of Sports Nutrition, 6, 3.

Mangels, A. R., Messina, V., & Melina, V. (2003). “Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets”. J Am Diet Association, 103(6), 748-765.

Martin, W. F., Armstrong, L. E., & Rodriguez, N. R. (2005). “Dietary protein intake and renal function”. Nutrition & Metabolism, 2, 25.

Phillips, S. M. (2006). “Dietary protein for athletes: From requirements to metabolic advantage”. Applied Physiology, Nutrition, and Metabolism, 31(6), 647-654.

Rand, W. M., Pelett, P. L., & Young, V. R. (2003). “Meta-analysis of nitrogen balance studies for estimating protein requirements in health adults”. The American Journal of Clinical Nutrition, 77(1), 109-127.

Rose, W. C., Wixom, R. L., Lockhart, H. B., & Lambert, G. F. (1955). “The amino acid requirements of man. XV. the valine requirement; summary and final observations”. 217: 987-995, The Journal of Biological Chemistry.

Rose, W. C. (1938). “The nutritive significance of the amino acids”. Physiological Review, 18, 109.

Schaafsma, G. (2000). “The protein digestibility-corrected amino acid score”. Journal of Nutrition, 130(7), 1865S.

Tarnopolsky, M. (2004). “Protein requirements for endurance athletes”. Nutrition, 20(7-8), 662-668.

Tarnopolsky, M. A., Atkinson, S. A., MacDougall, J. D., Chesley, A., Phillips, S., & Schwarcz, H. P. (1992). “Evaluation of protein requirements for trained strength athletes”. Journal of Applied Physiology, 73(5), 1986.

Tarnopolsky, M. A., MacDougall, J. D., & Atkinson, S. A. (1988). “Influence of protein intake and training status on nitrogen balance and lean body mass”. Journal of Applied Physiology, 64(1), 187.

Venderley, A. M., & Campbell, W. W. (2006). “Vegetarian diets: Nutritional considerations for athletes”. Sports Medicine, 36(4), 293.

Wilson, J., & Wilson, G. J. (2006). “Contemporary issues in protein requirements and consumption for resistance trained athletes”. Journal of the International Society of Sports Nutrition, 3(1), 7.


Nathan Payne [department writer] graduated from Ryerson University with a degree in Food and Nutrition. Currently he volunteers in health promotion and community gardening. He also continues to develop his interest in visual arts.