Advanced Sports Nutrition by Dan Benardot

Author:Dan Benardot
Language: eng
Format: epub, pdf
ISBN: 9781450419963
Publisher: Human Kinetics

FEMALE ATHLETES

A quick review of the dietary reference intakes (DRIs) demonstrates clearly that females have different nutrient requirements than males. Many of the requirement differences are based on body size (males being larger than females) and differences in body composition (males have a higher metabolic mass), but some are due to clear physiological differences, as is the case with iron (females require twice as much) because of the blood-iron loss associated with normal menses.

Energy intakes, for all athletes, are based on total weight, weight of the metabolic mass, and duration and intensity of exercise. Surveys of female athletes commonly report an underconsumption of energy, leading many to conclude that female athletes are at an elevated risk of developing eating disorders regardless of the type of sport they are participating in.4 In addition, the literature is filled with reports of the impact intense exercise has on the female reproductive system, with amenorrhea or oligomenorrhea a common outcome. These reports suggest that increasing energy intake to offset the high energy demand may be sufficient to reverse the menstrual dysfunction and halt the associated reduction in bone mass.5 The reduction in bone mass caused by menstrual dysfunction is clinically relevant for female athletes because it places them at current increased risk for stress fractures and later increased risk for osteoporosis. Amenorrhea is associated with lower circulating estrogen, which is an inhibitor of osteoclasts, the cells that break down bone. As a result, amenorrheic and oligomenorrheic athletes are at high risk for developing low bone density. In one study of 46 female athletes (31 with multiple stress fractures and 15 without stress fractures), nearly half of all athletes with stress fractures had menstrual irregularities, with a particularly high prevalence observed in endurance runners with high weekly training mileage.6 Although consuming sufficient calories and calcium will not correct the biomechanical factors associated with stress fractures, often associated with a high longitudinal foot arch and leg-length inequality, it will substantially reduce risk if this strategy helps females return to normal menstrual function.7 See table 11.1 for stress fracture risks.

The energy substrate distribution is of interest to female athletes. Studies indicate that females have a higher lipid, lower glycogen (carbohydrate), and lower protein utilization than do male athletes during endurance exercise.8 Because glycogen storage is limited, the lower rate of glycogen utilization gives female athletes what appears to be a clear advantage over men in long-duration, lower-intensity athletic events.9 This also gives rise to the following question: Should female endurance athletes have a different energy substrate consumption pattern than male endurance athletes given the difference in the pattern of substrate utilization? No solid evidence indicates there should be a difference in intake, and the nature of endurance and ultraendurance events still makes carbohydrate storage (glycogen) the limiting substrate in performance. Whether an endurance athlete is male or female, when glycogen is depleted the athletic performance will drop (or stop). A series of studies assessing the carbohydrate consumption pattern of female athletes involved in different sports indicated a wide range of intakes (see table 11.

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