Nutrition for the Female Athlete - Part 2
In the last issue of SSC, I highlighted that female athletes tend to have a lower energy intake relative to body weight than their male counterparts. This puts female athletes at a greater risk of developing certain micronutrient imbalances or deficiencies, especially iron, vitamin D and calcium, which are key to their physiology.
The female athlete’s micronutrient needs and intake
Iron is a vital micronutrient as its main function is to transport oxygen from the lungs to the exercising muscles by binding it to red blood cells. This is especially critical for the female athlete since women experience greater iron losses during menstruation. Another mechanism by which female athletes may experience greater losses is acute inflammation from strenuous exercise, during which high levels of IL-6 (interleukin-6) stimulate the expression of hepcidin. This hormone regulates iron homeostasis by affecting its absorption and promoting its export from red blood cells. For this reason, female athletes may find it hard to meet their iron needs, even more so if they restrict their energy intake or adopt a vegetarian/vegan lifestyle that could lead to iron deficiency anaemia (IDA). To prevent IDA and maintain an adequate iron status, a diet with highly bioavailable sources such as red meat, seafood and certain legumes is encouraged. However, athletes who have been diagnosed with IDA may benefit from iron-enriched foods or supplementation under the supervision of a dietitian or registered sport and exercise nutritionist.
Vitamin D and calcium are known to be vital for optimal bone health. In addition, vitamin D has been under the radar a lot in the last few years as it seems to support the immune system and muscle function, which are key to performance (see my article on the effects of vitamin D supplementation on athletic performance – link here). Vitamin D deficiency is normally indicated by a serum level of ≤20 ng/mL (approximately 50 nmoL/L). Female athletes should test their levels regularly and those who present deficiency are most likely to benefit from supplementing with 4000-5000IU for 8-12 weeks to help reach healthy levels. More importantly, more sunlight exposure and the intake of foods rich in vitamin D, such as oily fish and mushrooms, are also encouraged. Calcium may also need to be supplemented due to losses through sweat, especially in female amenorrheic athletes who present inadequate estrogen levels. Amenorrheic athletes have an additional requirement of 500mg/day of calcium to maintain their calcium balance and, therefore, may require an additional 1000mg/day.
The duration of supplementation will depend on the severity of the deficiency, however, this can normally be over a number of years. Nevertheless, female athletes are encouraged to establish healthy habits by eating calcium-rich foods such as dairy products, leafy greens, peanuts and sardines, since the effects of calcium supplementation are short-lived after its termination.
Hydration for the female athlete
Women tend to have lower sweating rates than men, mainly because of their smaller body size and lower metabolic rate during exercise. Moreover, during the luteal phase of the menstrual cycle (after ovulation until the period commences), when the female sex hormones (estrogen and progesterone) are elevated, the body core temperature increases by up to 0.6ºC1. This increases sodium losses and there is a higher rate of water turnover, which puts the female athlete at a greater risk of hyponatraemia (when serum sodium levels are too low) or dehydration during exercise. Research has shown that there is a higher prevalence of hyponatraemia in female athletes following long endurance events such as marathons and ironmans, which can be explained by the fact that they require less overdrinking than their male counterparts to dilute serum sodium concentration. There is also some evidence to suggest that women who develop hyponatraemia and have naturally higher estrogen levels are more likely to suffer from permanent brain damage or even die. This is thought to be due to the inhibitive effect of estrogen on the sodium-potassium ATPase enzyme, a protein that is responsible for moving potassium out of the brain cell, which in turn counteracts the influx of more fluid into the brain cell.
While there are no specific recommendations for the female athlete, they should pay particular attention to their hydration and favour electrolyte intake during training sessions, especially during the luteal phase. The current consensus is that any athlete should try not to lose more than 2% of their body weight during a race or competition; however, most importantly, each athlete should practice their own hydration strategies as sweating rates are highly variable.
Having an adequate dietary intake with proper nutritional strategies that match training demands is key to any successful athlete. But we must recognise the physiological and psychological differences between male and female athletes, and the need for more research on the female athletic population in order to design specific nutritional recommendations. Only in this way, can we, as dieticians and registered sport and exercise nutritionists, ensure that the female athlete’s health and well-being are in the right place for an optimal performance.
Deldicque, L. & Francaux, M. (2015). Recommendations for healthy nutrition in female endurance runners: an update. Front. Nutr; 2:17.
De Souza, MJ., Nattiv A., Joy, E., et al. (2014). Female athlete triad coalition consensus statement on treatment and return to play of the female athlete triad: 1st International Conference held in San Francisco, California, May 2012 and 2nd International Conference held in Indianapolis, Indiana, May 2013. Br J Sports Med; 48:289.
Murray, B., Stofan, J. Eichner, E. (2003). Hyponatremia in Athletes. Sports Sci Exchange 88; 16:1.
Potgeiter, S. (2013). Sport nutrition: A review of the latest guidelines for exercise and sport nutrition from the American College of Sport Nutrition, the International Olympic Committee and the International Society for Sports Nutrition. S Afr J Clin Nutr; 26(1):6-16.