Nutritional survey of highly trained women runners

Vitamin and mineral supplementation to athletes

Vitamin and mineral supplements are frequently used by competitive and recreational athletes. Dietary deficiencies of most vitamins are not very common among athletes except in those who restrict their food intake in order to maintain body weight. Vitamins most likely to be deficient in the diet are folate, B6, B12, and E. Biochemical evidence of vitamin deficiencies in some athletes have been reported for thiamine, riboflavin, and B6. When the diet is deficient, vitamin supplements may improve performance but are not likely to be effective if the dietary intake is adequate. Some female athletes' diets are low in calcium, iron, and zinc. Low calcium intake may reduce peak bone mass in young women. Iron deficiency may impair performance and needs to be corrected with an iron supplement. Zinc supplements that exceed the RDA interfere with the absorption of copper and lower HDL-cholesterol.

Minerals: exercise performance and supplementation in athletes

This paper examines whether mineral supplements are necessary for athletes, and whether these supplements will enhance performance. Macrominerals (calcium, magnesium, and phosphorus) and trace minerals (zinc, copper, selenium, chromium, and iron) are described. Calcium supplements are important for the health of bones. Athletes tend to have enhanced calcium status as assessed by bone mineral density, with the notable exception of female amenorrhoeic athletes. Magnesium status is adequate for most athletes, and there is no evidence that magnesium supplements can enhance performance. Phosphorus status is adequate for athletes. Phosphorus supplementation over an extended period of time can result in lowered blood calcium, however, some studies have shown that acute 'phosphate loading' will enhance performance. Athletes may have a zinc deficiency induced by poor diet and loss of zinc in sweat and urine. Limited data exist on the relationship of performance and zinc status. Widespread deficiencies in copper have not been documented, and there are no data to suggest that copper supplementation will enhance performance. There is no reason to suspect a selenium deficiency in athletes. The relationship between selenium status and performance has not been established, but selenium may play a role as an antioxidant. Because of the low intakes of chromium for the general population, there is a possibility that athletes may be deficient. Exercise may create a loss in chromium because of increased excretion into the urine. Many athletes, particularly female, are iron depleted, but true iron deficiencies are rare. Iron depletion does not affect exercise performance but iron deficiency anaemia does. Iron supplements have not been shown to enhance performance except where iron deficiency anaemia exists. In conclusion, poor diets are perhaps the main reason for any mineral deficiencies found in athletes, although in certain cases exercise could contribute to the deficiency. Mineral supplementation may be important to ensure good health, but few studies have definitively documented any beneficial effect of mineral supplementation on performance.

Discrepancies between energy intake and expenditure in physically active women

Energy intake and expenditure in women runners and non-runners were assessed by weighed food records, evaluation of minute-by-minute activity diaries, and indirect calorimetry. All participants were adapted to their stated activity levels for at least 6 months and maintained a constant body-weight throughout their participation. Calculated daily energy intake equalled calculated expenditure in non-runners (7300 (SD 1536) v. 7476 (SD 872) kJ/d), but calculated energy expenditure in women running about 54 km/week was found to exceed intake by more than 2700 kJ/d (8259 (SD 1466) v. 10963 (SD 1367), P less than 0.01). The runners showed no evidence of compensating for the increased energy expenditure associated with running by engaging in lower-intensity activities during non-running time. Further, runners did not decrease energy expended at various activities. The findings suggest that women adapted to high levels of activity may possess mechanisms to maintain body-weight without significantly increasing energy intake.

Repeated Stress Fractures in an Amenorrheic Marathoner

This case conference is one of a series presented at the annual meeting of the American College of Sports Medicine, Dallas, May 1988.

Effects of exercise training on human copper and zinc nutriture

The findings of our three studies indicate no significant decreases in blood biochemical indices of copper and zinc nutritional status among female and male swimmers during physical training when dietary intakes of these trace elements are adequate (greater than or equal to 67% recommended safe and adequate intake). At these intakes, erythrocyte superoxide dismutase activity increased after physical training indicating a biochemical adaptation of human copper metabolism associated with exercise training. It is noteworthy that this increase in superoxide dismutase activity occurred without an apparent increase in daily copper intake. The calculated copper intakes were 1.3-1.4 and 1.6-1.9 mg/d in the female and male swimmers, respectively. These intakes are less than the suggested value of 2.0 mg/d (Committee on Dietary Allowances, 1980), but they are similar to the reported intakes of other groups in the United States (Klevay et al., 1979). In conclusion, these findings do not appear to support the belief that physical training per se produces adverse effects on copper and zinc nutriture.

Trace nutrients. 5. Minerals and vitamins in the British household food supply

1. The amounts of magnesium, copper, zinc, phosphorus, manganese, potassium, vitamin B6, vitamin B12, folate, pantothenic acid, biotin, vitamin E and dietary fibre in the British household diet were calculated by applying appropriate values from recent analytical studies to the amounts of foods recorded in the National Food Survey during 1986. 2. National average intakes were (mg/person per d): Mg 247, Cu 1.25, Zn 9.0, P 1249, Mn 3.43, K 2694, vitamin B6 1.73, vitamin B12 6.33 micrograms, folate 230 micrograms, pantothenic acid 6.07, biotin 35 micrograms, vitamin E 8.4. Regional and income-group differences were estimated, and found to be small. Additional contributions from alcoholic drinks and confectionery were also determined. 3. Dietary fibre was estimated both as unavailable carbohydrate and as non-starch polysaccharide. The national average intakes were 21.8 and 12.9 g/d respectively. 4. Intakes were compared with Canadian (Department of National Health and Welfare, 1983) and American (National Research Council, 1980) recommended dietary allowances (RDAs). With the exception of biotin, the Canadian RDAs were met by the household diet but the much higher American RDAs were only met for vitamin B12 and pantothenic acid.

Nutrition Education for Elite Female Runners

In brief: Suboptimal nutrition practices that may limit performance and promote injury prevail even among informed top competitors. A survey of the dietary habits of elite female runners showed that while most do fuel themselves with nutritious foods, others in the group only believe they eat wisely (but actually may have a suboptimal intake), and still others exist on hit-or-miss nutrition habits. The authors review the characteristic eating patterns, nutrition knowledge, and attitudes about body weight and food in this group of athletes, and recommend ways to counteract their performance-limiting habits.