Meatless Diets in Female Athletes: A Red Flag
Alvin R. Loosli, MD; Jaime S. Ruud, MS, RD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 11 - NOVEMBER 98
In Brief: Physically active adolescent girls and young women may eliminate meat from their diets to achieve or maintain low body weight. By doing so, they risk developing protein, iron, and zinc deficiencies. Further, meatless diets in this population may signal the possibility of amenorrhea and/or disordered eating, with the attendant risk of osteoporosis. Educating young women and their parents and coaches regarding the risks of a meatless diet and using the preparticipation exam to screen for these problems can promote preventive measures.
In a survey of 854 adolescent girls and young women, Moore (1) reported that 67% were dissatisfied with their weight, and 54% were dissatisfied with their body shape.
These figures reflect the enormous pressure on today's young women to be attractive and achieve a certain body weight. The resulting preoccupation with weight has been attributed to American cultural values and the media's depiction of women (2).
Whatever the cause, female athletes can also be preoccupied with body weight and shape, and this is especially true of those who must maintain a low body weight for their sport (3). For example, Wiita and Stombaugh (4) reported that 25% of 22 female adolescent runners were unhappy with their weight and felt pressure from coaches and parents to be thin.
In an effort to reach or maintain an ideal weight, female athletes may avoid eating meat because they think it is fattening (5). This is not a step toward true vegetarianism for religious, moral, or environmental purposes but rather one taken under the sway of distorted beliefs about food, body weight, and nutrition (6). For this reason, a meatless diet in a female athlete should be a red flag to physicians, trainers, and other healthcare professionals, because it may indicate potential problems for the athlete that include inadequate intake of protein, iron, and zinc as well as amenorrhea and serious eating disorders.
Diets that do not include animal food such as meat, chicken, and fish tend to be low in protein. In a study (4) in which adolescent female runners underwent dietary analyses twice in 3 years, the runners limited their consumption of beef, milk, and cheese, and their daily protein intake decreased significantly from 1.6 g per kilogram of body weight to 1.1 g/kg. While these values are higher than the US Department of Agriculture's Recommended Dietary Allowance (RDA), the runners' daily protein intakes were lower than those recommended for endurance athletes (1.2 to 1.7 g/kg) (7).
Furthermore, the runners' mean daily energy intake decreased from 2,150 kcal to 1,647 kcal over the 3 years. Given their average height, weight, and activity level, these female adolescent runners should have consumed closer to 2,500 kcal. Insufficient energy intake increases protein requirement, because more protein is needed to maintain nitrogen balance when energy intake is low. In addition, female athletes who avoid meat may also limit their intake of chicken, fish, and eggs—important dietary sources of high-quality protein.
Iron and Zinc
Female athletes who eliminate meat from their diets may not take in enough of two key minerals, iron and zinc (8).
Getting enough iron is a particular concern for those who do not eat meat because the body's absorption of iron depends on the form of iron in foods. Meat contains heme iron, which is absorbed at a much greater rate than the nonheme iron found in plant foods (15% to 35% vs 2% to 20%) (9). The rate of absorption depends on dietary substances that enhance absorption (ascorbic acid) or inhibit it (tannins, wheat, bran) and on the amount of iron stores. Meat promotes the absorption of both nonheme and heme iron and is currently the only dietary factor known to influence heme iron absorption. Ascorbic acid found in citrus fruits enhances the absorption of iron from nonheme food sources.
Snyder et al (10) reported that the bioavailability of iron was significantly lower in female runners who ate a modified vegetarian diet (less than 100 g of red meat per week) than in those who regularly ate red meat (0.66 mg vs 0.91 mg per day). Both groups had similar total calorie intakes and consumed similar amounts of dietary iron (about 14 mg/day). However, the athletes who ate red meat consumed more heme iron than the others (1.2 vs 0.2 mg/d) and also had significantly higher serum ferritin levels.
Decreased consumption of red meat and low calorie intake explain why female athletes have difficulty meeting the RDA of 15 mg of iron. Surveys (11) of female athletes show mean daily energy intakes ranging from 1,706 to 3,572 kcal, with an average of 13 mg/d of iron.
Low dietary iron intakes can contribute to iron deficiency, one of the most common nutritional deficiencies in the United States. Data from the Third National Health and Nutrition Examination Survey (12) indicated that 9% to 11% of adolescent girls and young women have iron deficiency, and 2% to 5% have iron-deficiency anemia.
Iron deficiency is associated with many adverse health effects, including changes in immune function, cognitive development, temperature regulation, energy metabolism, and work performance (13). Subtle negative effects of iron deficiency, such as fatigue and lack of concentration, can be magnified with intense training (14). Female athletes who have low iron stores also risk illness and injury and thus may reduce their ability to train and compete (8).
Similarly, zinc intake and absorption are influenced by the amount of animal products in the diet. Meat, liver, eggs, and oysters are among the best sources of dietary zinc and provide about 70% of the zinc consumed by most people in the United States (15). Furthermore, meat contains a more easily absorbed form of zinc than plant foods, and high amounts of dietary fiber, phytic acid, and oxalic acid—substances found in plant foods—may interfere with zinc absorption. Thus, the athlete who avoids animal foods may have trouble meeting daily requirements for zinc, especially if caloric intake is low.
The RDA for zinc is 12 mg for women. The average daily intake for sedentary and athletic women in the United States is about 10 mg. One study (16) reported that vegetarian women had significantly lower mean daily zinc intakes than nonvegetarian women (8 mg vs 11 mg).
Meatless diets have also been linked to menstrual abnormalities (17-21). Pedersen et al (21) reported that the prevalence of menstrual irregularities among 41 nonvegetarian women was 4.9%, vs 26.5% among 34 vegetarian women.
Kaiserauer et al (18) compared nine regularly menstruating runners with eight amenorrheic runners and seven regularly menstruating controls with regard to nutrient intakes, estrogen levels, and physical characteristics. The amenorrheic subjects consumed significantly less total fat and calories than eumenorrheic runners, and they ate no red meat, while 44% of the eumenorrheic runners ate meat.
Slavin et al (19) found similar results in 128 recreational athletes and 36 elite female cyclists. Nine (7%) of the recreational athletes and 12 (33%) of the elite cyclists were amenorrheic, and none of the 12 cyclists ate red meat. Amenorrhea was present in 3 of the 84 recreational athletes (about 4%) who ate diets balanced from four food groups and in 6 of the 44 (about 14%) who ate high-carbohydrate, low-fat diets.
The primary health risk posed by amenorrhea is premature osteoporosis. Amenorrhea is associated with decreased bone mineral content of the lumbar spine (22-25) and increased risk of scoliosis (26) and stress fractures (27-28). More recent data have shown that amenorrheic athletes may have reduced bone mineral density at multiple skeletal sites (29). Noted sports nutritionist Nancy Clark has stated that eating small portions of red meat—4 to 6 oz two to three times per week—can be part of the solution for athletic amenorrhea (30).
Restrictive eating behaviors can lead to a multitude of nutrition-related health problems, the most serious of which are anorexia nervosa and bulimia nervosa. Though many factors account for an athlete's predisposition to eating disorders, including sports-related pressures, perfectionism, high expectations, low self-esteem, and emotional instability (31), a meatless diet may be a warning sign to healthcare professionals about a potential eating disorder.
In fact, a meatless diet has been associated with anorexia. Gadpaille et al (32) suggested a link between athletic amenorrhea and meatless diets in runners with eating disorders. Of 13 amenorrheic runners, 12 (87%) were vegetarians, and 8 (62%) had eating disorders diagnosed through a psychiatric interview according to criteria of the Diagnostic and Statistical Manual of Mental Disorders. Only 3 (about 16%) of the 19 menstruating runners were vegetarians, and none had diagnosed eating disorders.
In a recent cross-sectional study (33) of 107 female adolescents who did not eat meat and 214 who did, those who did not eat meat dieted twice as often, vomited four times as often, and used laxatives eight times as often as those in the meat-eating group.
Anorexia nervosa and bulimia can cause serious health consequences for patients, including intermittent hospitalization and death. Early identification of a disordered eating pattern may allow intervention and prevention of these conditions.
Female athletes who change their eating habits to reduce calories and fat may eliminate meat from their diets. These athletes, their coaches, and physicians should be aware that those who do not eat meat risk adverse effects on health, training, and performance. They are also at risk for eating disorders, amenorrhea, and osteoporosis, which are components of the female athlete triad, a syndrome seen in some physically active girls and young women. Any component of the triad can impair health and performance, and the presence of all three compounds the risk.
The American College of Sports Medicine recently published a position stand (34) on this syndrome. This is an important document that emphasizes prevention through the education of athletes, peers, parents, coaches, and healthcare professionals regarding the contributory psychological factors, warning signs, and outcomes of the triad.
The preparticipation exam is an ideal time for physicians to ask about weight, nutrition, menstrual function, and performance goals. At-risk athletes should be referred to a sports nutritionist who can assess dietary habits and provide sound nutrition information.
Female athletes who consume no meat may seek to legitimize their restrictive eating behaviors by calling themselves vegetarians. Although it is theoretically possible to compete athletically on a meatless diet, it requires much education and commitment. Those who wish to do so should be informed about the risks and educated about eating a balanced diet that includes alternative sources of protein, iron, and zinc, since these may not be adequately available from certain plant foods. They should also be screened for disordered eating and amenorrhea, and if either is found, for osteoporosis; screening for iron-deficiency anemia is also important.
Dr Loosli practices at the Center for Sports Medicine at St Francis Memorial Hospital in San Francisco. He is an instructor in family practice at the University of California at Davis School of Medicine and is an editorial board member of The Physician and Sportsmedicine. Ms Ruud is a nutrition consultant with Nutrition Link in Lincoln, Nebraska. Address correspondence to Alvin R. Loosli, MD, Center for Sports Medicine, St Francis Memorial Hospital, 900 Hyde St, San Francisco, CA 94109.
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