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Concerns: Vegetarian Athletes

Eating a well-balanced diet containing adequate amounts of calories, protein, vitamins, and minerals is critical for optimal health and peak performance.   Several athletes are challenged to obtain these key nutrients due to incorporation of a vegetarian lifestyle, which restricts the intake of all (vegan) or a selected variety of animal-based foods. Athletes who merely restrict intake of animal foods as means to control weight or those who simply lack the knowledge are at high risk for unfavorable changes in metabolic efficiency, altered hormonal status, diminished bone health, and nutritional deficiencies, all of which can severely inhibit peak performance.

 

Risk #1:  Unfavorable Changes in Metabolic Efficiency Athletes can expend extraordinary amounts of energy during training and competition.  In fact, it has been estimated that endurance athletes require anywhere from 16-30 calories per pound of body weight to meet the high demands of endurance training.  Energy needs in vegetarian athletes may be even higher, as resting energy expenditure has been shown to be ~11% higher in vegetarians compared to nonvegetarians.1  Because vegetarians eat lots of high-fiber low-fat foods (whole grains, fruit, vegetables), it is not uncommon to discover inadequate energy intakes in vegetarian endurance athletes, especially those expending greater than 1,000 calories per day.2  When energy expenditure exceeds intake by over 1,000 calories, there is significant catabolism of lean body mass, leading to a drop in metabolic efficiency as well as endurance performance.3 For those vegetarian athletes who have trouble keeping weight on, it is recommended to eat 6 or more medium-sized meals/snacks containing such energy dense plant foods as nuts, avocado, dried fruits, and dairy products.  

 

Risk #2:  Nutritional Deficiencies  Protein: Protein is perhaps the most recognized nutrient of concern in vegetarians due to the incomplete nature and reduced digestibility of most plant sources of protein.  With the exception of soybeans, milk, and egg whites, other vegetarian based foods lack all the essential amino acids necessary for maximal tissue growth and repair.  Most vegetarian based foods need to be combined to attain all the essential amino acids; for example, tortillas and beans, rice and lentils, peanuts and wheat bread.  Endurance athletes require 0.55 to 0.75 grams of protein per pound of body weight, which is approximately 150%-200% the US RDA for protein intake.  Additional amounts of protein are needed to replace the loss of amino acids during exercise and to help repair exercise-induced muscle damage that occurs during weight-bearing activity such as running.  The World Health Organization suggests that vegetarian endurance athletes consume 110% of their calculated protein requirement because of the reduced protein digestibility of plant foods, which is attributable to the high fiber content of the diet.4  Vegetarian diets providing adequate energy and a variety of protein-containing plant foods will supply all the essential amino acids needed for efficient protein metabolism, thereby enhancing recovery from exercise and helping to prevent muscular injury. Calcium: Calcium becomes an especially vulnerable nutrient for vegetarians who do not consume dairy products.  A chronic low calcium intake, especially when combined with an inadequate energy intake, is associated with decreased bone mineral density, leading to elevated risk for bone fracture.5 Furthermore, a calcium deficiency may lead to severe cramping during endurance exercise as calcium plays a critical role in normal muscle function.  Recommended intake of calcium ranges from 1,000 mg to 1,500 mg depending on the individual.  Good non-dairy sources of calcium include calcium-fortified foods, calcium-processed tofu (4 ounces = 145 mg), almonds (1 ounce = 332 mg), legumes (1 cup = 90 mg), and collard greens (1/2 cup = 179 mg). Vitamin B12: Vitamin B12, which is present naturally only in animal products, is essential for maintaining healthy red blood cells and nerve fibers. Vegetarians who restrict energy intake may be at elevated risk for a deficiency, leading to premature fatigue during exercise and potential nerve damage.  Fortunately, the US RDA (2.4 mcg) for Vitamin B12 is very small and quite easy to attain in such fortified plant sources as soy milk, soy burgers, nutritional yeast, and certain breakfast cereals (such as Total or Product 19). Iron: Iron, a trace mineral, is a major component of the body’s red blood cells or hemoglobin, whose role is to carry oxygen to various body tissues, including muscle, for use during aerobic activity.  A blood deficiency in iron may lead to premature fatigue during exercise due to lack of oxygen transport to working muscles.  While iron is found extensively in several plant foods, the absorption is reduced by 20% as compared to the iron found in animal products.6 Therefore, the risk for iron deficiency is increased in vegetarian athletes even if total iron intake meets the US RDA of 10-15 mg. For added absorption of vegetarian iron sources, consume with foods rich in vitamin C (such as orange juice). Zinc: Along with iron, a zinc deficiency tops the list of the most common dietary deficiencies among vegetarian athletes, perhaps due to urinary and sweat losses during heavy trainingand/or the fact that plant sources of zinc (such as legumes, whole grains, wheat germ, fortified cereals, nuts, tofu, and miso) are not absorbed as efficiently as animal sources of zinc.6,7  A study of female distance runners discovered that 50% fell below the recommended daily intake for zinc (12 mg/day), which may lead to an altered zinc status.8  An altered zinc status will compromise immune function as well as basal metabolic rate and thyroid hormone levels, which can have a major impact on endurance performance and health.9  Fortunately, a recent study from the US Department of Agriculture found that zinc status can be maintained within normal limits with a vegetarian (lacto-ovo) diet that includes such zinc-rich foods as beans, milk, yogurt, tofu, and peanut butter.10  

 

Risk #3:  Altered Hormonal Status There has been some concern that vegetarian athletes are at increased risk for altered hormonal status, especially with the sex hormones estrogen and testosterone.11 In a study of 8 male endurance athletes, engagement in a lacto-ovo-vegetarian diet over a period of 6-weeks caused a slight decrease in total testosterone levels.12  Similarly, female vegetarian athletes have reported lower circulating estrogen levels as compared to their meat-eating counterparts.13  However, it is unclear whether hormonal function diminishes as a result of the food composition in a vegetarian diet or simply a reduction of total energy intake. Some studies have found that plant-based diets, with their high fiber content, report greater loss of sex hormones in feces as compared to non-vegetarian diets.12 Vegetarians also tend to have lower intakes of protein15, fat11, and zinc16 as compared to omnivores.  More recent research suggests that the cessation of hormonal function is merely an energy conserving adaptation to an energy-deficit profile, which can be caused by reduced energy intake or by an extremely high energy expenditure from chronic intense exercise, or by a combination of the two.17,18,19 Regardless of the cause, altered hormonal status can lead to serious health and fitness implications.  Symptoms of altered hormonal status include fatigue, weight loss, frequent infections, decreased physical performance, diminished bone health, and increased injury.  In order to maintain normal hormonal status, vegetarians should follow a well-balanced diet that meets individual energy needs. As the popularity of plant-based diets increase within the athletic arena, the risk for poorly planned diets and consequent nutritional deficiencies also increases.  A negative energy imbalance not only compromises metabolic efficiency, but also seems to negatively affect hormonal status, bone health, and nutritional intake of protein, calcium, vitamin B-12, iron, and zinc.  Sub sufficient intakes of these nutrients will have a profound negative effect on health and endurance performance.  However, an athlete can reap many benefits, both performance-based and health-based, from a balanced vegetarian diet.

 

By Kimberly J Mueller MS, RD

Owner of Fuel-Factor (fuel-factor.com)

 

REFERENCES

  1. Coggan AR, Swanson SC.  Nutritional manipulations before and during endurance exercise: effects on performance. Med Sci Sports Exerc. 1992; 24: S331-S335.
  2. Grandjean A.  The vegetarian athlete. Phys Sports Med. 1987; 15: 191-194.
  3. Willmore J, Costill D. Physiology of Sport & Exercise (2nd Ed). Champaign, IL:  Human Kinetics, 1999.
  4. World Health Organization Technical Report Series 724. Energy and protein requirements. Report of a joint FAO/WHO/UNU expert consultation. 1985.
  5. Myburgh KH, Hutchins J, Fataar AB, Hough SF, Noakes TD. Low bone density is an etiologic factor for stress fractures in athletes. Ann Int Med. 1990; 113: 754-759.
  6. Hurrell RF. Bioavailability of iron. Eur J Clin Nutr. 1997; 51: S4-S8
  7. LuKaski H. Micronutrients (magnesium, zinc, and copper): are mineral supplements needed for athletes? Int J Sports Nutr. 1995; 5: S74-S83.
  8. Duester PA, Day BA, Singh A, Douglass L, Moser-Veillon PB.  Zinc status of highly trained women runners and untrained women. Am J Clin Nutr. 1989; 49: 1295-1301.
  9. Wada L, King J.  Effect of low zinc intakes on basal metabolic rate, thyroid hormones, and protein utilization in adult men.  J Nutr. 1986; 48(116): 1045-1053.
  10. Kaiserauer S, Snyder A, Sleeper M, Zierath J. Nutritional, physiological, and menstrual status of distance runners. 1989; 21: 120-125.
  11. Kaiserauer S, Snyder A, Sleeper M, Zierath J. Nutritional, physiological, and menstrual status of distance runners. 1989; 21: 120-125.
  12. Raben A, Kiens B, Richter EA, Rasmussen LB, Svenstrup B, Micic S, Bennett P. Serum sex hormones and endurance performance after a lacto-ovo vegetarian and a mixed diet. Med Sci Sports Exerc. 1992; 24: 1290-1297.
  13. Goldin BR, Adlercreutz H, Gorbach SL, Warram JH, Dwyer JT, Swenson L, Woods MN. Estrogen escretion patterns and plasma levels in vegetarian and omnivorous women. N Engl J Med. 1982; 307: 1542-1547.
  14. Nelson M, Fisher E, Catsos P, Meredith C, Turksoy R, Evans W. Diet and bone status in amenorrheic runners. Am J Clin Nutr. 1986; 43: 910-916.
  15. Duester PA, Kyle SB, Moser PB, Vigersky RA, Singh A, Schoomaker EB. Nutritional intakes and status of highly trained amenorrheic and eumenorrheic women runners. Fertil Steril. 1986; 46: 636-643.
  16. Duester PA, Kyle SB, Moser PB, Vigersky RA, Singh A, Schoomaker EB. Nutritional intakes and status of highly trained amenorrheic and eumenorrheic women runners. Fertil Steril. 1986; 46: 636-643.
  17. Yaeger KK, Agostini R, Nattiv R, Drinkwater B. Female athelte triad: disordered eating, amenorrhea, osteoporosis. Med Sci Sports Exerc. 1993; 25: 775.
  18. Zanker CL, Swaine IL. The relationship between bone turnover, oestrodiol, and energy balance in women distance runners. B

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