Sports Fitness Training

Excess protein has been considered by many nutritional experts to be hazardous to the health of athletes. According to research from the Medlantic Research Foundation, “Protein intake is more than adequate in the USA and further increases could have negative effects on the prevalence of renal disease and osteoporosis.” Certainly, there is little evidence in active, athletic individuals that high-protein consumption is harmful to one’s health.Because of the kidney’s role in processing and ridding the body of nitrogenous waste, this organ could be particularly susceptible to damage from being overworked. Theoretically, large amounts of nitrogen from a high-protein diet may become toxic. Despite its role in nitrogen excretion, there are presently no data in the peer-reviewed scientific literature demonstrating the normal kidney will be damaged by the increased demands of protein consumed in quantities above the RDA. Furthermore,real world examples support this contention as kidney problems are nonexistent in the body­building community in which high-protein has been the norm for over half a century.

Researchers Poortmans and Dellalieux from the Department of Physiological Chemistry, Institute of Physical Education and Kinesiotherapy at Free University in Brussels, Belgium, studied the effects of a high- and medium-protein intake in bodybuilders and other well-trained athletes. Subjects underwent blood and urine sampling in addition to keeping a 7-day record of their food intake. Data demonstrated that despite higher plasma concentrations of uric acid and calcium, the group of bodybuilders on the high-protein diet had normal renal clearance of creatinine, urea, and albumin. Interestingly, the nitrogen balance for both groups became positive when daily protein intake exceeded 1.26 g/kg. Researchers concluded that protein intake under 2.8 g/kg/ day does not impair renal function in well-trained athletes.

Animal data enforce the belief that a high-protein diet does not damage the mammalian kidney. This lack of toxicity is present even at extremely high amounts for prolonged periods of time. Zaragoza and colleagues fed rats a dietary regimen in which protein constituted 80% of their energy intake for more than half of their life span. In spite of the amount of protein and the time of administration, no deleterious effects were noted.

High-protein diets may increase the excretion of calcium, a particular concern to women at risk for osteoporosis. However, work by Orwell and Porter & Johnson suggest that increased protein intake is often beneficial and associated with anabolic processes in bone. In a study published in Calcified Tissue International, Cooper et al. studied bone density (dual-photon absorptiometry in the lumbar spine and proximal femur and single-photon absorptiometry in the distal and mid-radius) in 290 women ranging from 30 to 94 years of age. Dietary information on calcium, phosphorus, vitamin D, protein, fat, and total energy were obtained from a 7-day food record. Among the premenopausal women studied, there was a statistically significant positive association between protein intake and bone mineral content in the distal radius and proximal femur. Postmenopausal women showed no relationship between protein and bone mineral content. From the food record, all of the women studied consumed a mean of 75 g/day of protein.These results suggest that dietary protein consumption may be a determinant of the peak bone mass attained by premenopausal white women. They further commented that the finding of a positive association between protein consumption and bone mineral content was a surprise because animal and human studies on calcium metabolism show excess urinary excretion of the mineral as protein intake increases. According to work by Freudenheim et al., it is possible that the hypercalciuric effect of protein is offset by a hypocalciuric effect of phosphorus, which is present in substantial quantities in diets high in meat protein. In women who engage in strength training, any hypercalciuric effect of protein may be offset by the strong effect this mode of exercise has on increasing bone density. There may be further benefits on bone from a high-protein diet and weight training via increased insulin-like growth factor-1, which has been shown to have a positive effect on bone mass. Levels of this peptide hormone have been shown to increase in strength-trained subjects after a protein-carbohydrate supplement and in those who consume a protein supplement after hip fracture.

Atherogenic effects of high-protein diets have been over­ stated, especially in regards to athletic populations. In the past, strength athletes and football players (especially offensive and defensive linemen) were known for consuming protein sources that were high in saturated fat such as various forms of fast food, whole milk, and fatty cuts of beef. Today, athletes have access to protein sources that contain minimal amounts of fat like chicken breast without skin, fish, lean cuts of beef, and egg whites. Protein supplements available today contain little to no fat. To consider a diet high in protein that is also high in fat is an outdated concept. With the variety of lean, whole-food sources of protein and the multitude of protein supplements available, some athletes may need to be advised to consume additional fat in an effort to get sufficient calories to meet their daily requirement.