Nutritional Concerns of Vegetarian Athletes

Vegetarian diets are associated with a reduced risk of coronary heart disease, obesity, hypertension, dyslipidemia, non-insulin dependent diabetes, and some types of cancer. Compared to nonvegetarians, vegetarians have a lower risk of these chronic disease due to a higher intake of fruit and vegetables, dietary fiber, antioxidant nutrients, phytochemicals and folic acid, and a lower intake of saturated fat and cholesterol. Vegetarian diets, like all diets, need to be properly planned to be nutritionally adequate (see American Dietetic Association, 1997).

David Neiman, DrPH, a researcher at Appalachian State University in Boone, NC noted in a presentation at the 1997 International Congress on Vegetarian Nutrition that the available evidence does not support either a beneficial or detrimental effect of a vegetarian diet on athletic performance, especially when carbohydrate intake is controlled. Neiman also indicated that there is no convincing data that the vegetarian diet, in combination with heavy training, impairs health and/or athletic performance (see Neiman, 1998).

A high carbohydrate diet is recommended for athletes to maintain glycogen stores. At the high intensities required for training and competition, muscle and liver glycogen provide the major fuel for muscle contraction, and fatigue occurs when these reach low levels. A vegetarian diet that emphasizes plant foods such as whole grains, legumes, fruit, and vegetables facilitates a high intake of carbohydrate.

There is concern that a diet emphasizing plant foods increases both dietary fiber and phytic acid intake to levels that reduce the bioavailability of several nutrients, including zinc, iron, and trace minerals such as zinc, copper, manganese, and selenium. The nonheme iron from plant sources is also more poorly absorbed than heme iron from animal products. This may increase the risk of anemia in endurance athletes who are at greater risk of iron deficiency due to exercise-induced iron losses. The female adolescent athlete on a vegetarian diet may be at particular risk.

Despite the lower bioavailability of some trace elements in vegetarian diets, most studies have failed to demonstrate that vegetarians have impaired trace mineral status. Although vegetarian diets are higher in total iron content than nonvegetarian diets, serum ferritin and other iron status indicators are lower in vegetarians due to decreased iron absorption. However, iron deficiency anemia rates are similar in vegetarians and non-vegetarians (see American Dietetic Association, 1997).

Neiman recommends that vegetarian athletes increase their intake of good dietary sources of iron and zinc (e.g. fortified breakfast cereals, legumes, nuts and seeds), include vitamin C sources with each meal to enhance absorption of nonheme iron, and avoid heavy tea intake as tannic acid inhibits iron absorption. Iron, zinc, and trace element supplementation may be required for some vegetarian athletes who have poor diets, but supplements should not exceed 100% of the Recommended Dietary Allowance (RDA) to avoid negative interactions with the absorption or function of other nutrients (see Neiman, 1998).

Vegetarian athletes usually consume a diet rich in fruit, vegetables, and whole grains and so receive a high intake of antioxidant nutrients which may help to reduce the oxidative stress associated with heavy exercise. The value of antioxidant supplements in reducing exercise-induced oxidative stress remains controversial (see Neiman, 1998).

Plant sources of protein alone can provide adequate amounts of essential and non-essential amino acids as long as the athlete consumes a variety of foods and enough calories to meet energy needs. Legumes and soyfoods are good plant sources of protein and combining complementary proteins within the same meal is unnecessary. Most vegetarian diets meet or exceed the RDA for protein, but provide less protein than nonvegetarian diets. Though protein needs may be elevated due to heavy training, most vegetarian athletes can meet these extra demands without protein supplementation by consuming adequate calories and keeping protein intake near 15% of total calories (see Neiman, 1998).

Creatine is a popular ergogenic aid for athletes who engage in repeated bouts of short-term, high-intensity exercise such as sprinting or weight lifting. Research has shown that consuming 20 to 25 grams of creatine daily in divided doses for five days significantly increases muscle creatine levels, especially in individuals who have low levels initially. Vegetarians have a reduced body creatine pool due to avoidance of meat and represent a population that will likely be helped by creatine supplementation. However, further research is required since not all studies have found that creatine supplementation improves performance during short-term, high intensity exercise.

There is concern that a vegetarian diet places the female athlete at greater risk for amenorrhea and osteoporosis. High-fiber, low-fat vegetarian diets and large volumes of exercise have each been independently associated with reduced estrogen levels and amenorrhea. There is increasing evidence that low energy intake, rather than exercise stress or dietary quality, is the major cause of amenorrhea in athletes. Neiman notes that properly nourished vegetarian athletes have normal menstrual function when compared to matched nonvegetarian controls (see Neiman, 1998).

 

References

Position of the American Dietetic Association: vegetarian diets, Journal of the American Dietetic Association, 1997;97(11):1317-1321.

Neiman, DC, Fitness and vegetarian diets, American Journal of Clinical Nutrition, (supplement issue for the Third International Congress on Vegetarian Nutrition), 1998; in press.

Ellen Coleman, RD, MA, MPH
ellen@cruciblefitness.com