The Female Athlete Triad: It’s not normal!

Over the weekend I gave a presentation to a group of female mountain bikers. One of the many issues that came up was the prevalence of stress fractures in these endurance athletes. This was interesting to me as the study I conducted for my Master’s degree was on low bone density in male endurance athletes. In the discussion that followed, it emerged that some of the participants had, at one time or another, symptoms of the female athlete triad.

In 1993 the term the female athlete triad was coined by Yeager et al. to describe three interrelated conditions; low energy availability (with or without disordered eating), menstrual dysfunction, and low bone mineral density. In other words, not eating enough, irregular or absent periods, and weak bones. In fact, missing periods is quite common in elite female athletes. Particularly in sports where a low body weight is desirable , such as running, cycling, gymnastics, etc. What has emerged in the years since is that these symptoms are not simply part of being a female athlete, but signs that there is a problem.

Recent research has shown that low energy availability is what drives the other symptoms of the female athlete triad. Energy availability is the amount of dietary energy remaining for other body functions after exercise training.  It is calculated as dietary energy intake minus exercise energy expenditure. As fat doesn’t use any calories and has no effect on how much you need to eat per day, it is standardised per kilogram of fat free mass. So in my case, if I weight 65 Kg and am 26% fat, then my fat free mass is 48.1 Kg. If I eat 2000 kcal per day and burn 300 kcal through exercise, then my energy availability is 35.3 kcal per Kg fat free mass per day (2000 kcal minus 300 kcal divided by 48.1 Kg).

Bone tissue is constantly being turned over through remodelling, where bone resorption by osteoclasts is balanced by bone formation by osteoblasts. Studies have shown that having energy availability below 30 kcal/kg fat free mass/day reduces bone formation. So to protect my bones, I should never eat less than 1443 kcal per day (48.1 Kg fat free mass x 30). Moreover, the energy availability recommended for energy balance and best performance is around 45 kcal/kg fat free mass/day. Again, at my 48.1 Kg of fat free mass, that would be 2165 Kcal per day.

Low energy availability also has an effect on reproductive hormones, which in turn can impact bone. Luteinizing hormone pulsatility, as regulated by the pituitary gland, is also disrupted when energy availability falls below 30 kcal/kg fat free mass/day. As well as disrupting normal reproductive function, luteinizing hormone determines the release of oestrogen from the ovaries. Not only does this lead to absent or irregular periods, but oestrogen is a potent inhibitor of bone resorption. So the longer an athlete goes without having regular periods, the more likely it is her bones are being damaged. This increases their risk of stress fractures during training, and osteoporosis later in life.

Part of the problem is that we are unique individuals. Some athletes can maintain their bone and reproductive health at 12% body fat. Others lose their periods if they drop below 18% body fat.  So I would advise all female athletes to listen to their bodies. If you start missing periods, you either need to eat more or reduce your training load (or both). No matter your level or your sport, missing periods should not be normal and is not a symptom to be ignored!

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