In my latest blogs, I’ve highlighted what RED-S is (click here), how it differs from FAT (click here) and how it impacts male athletes (click here). I now want to transition to some of the health and performance outcomes of RED-S. More specifically, I want to talk about some of the less well-known consequences such as impacts on gastrointestinal function and immune health. Today, I’ll start with a more well-known outcome that I’ve briefly touched on, menstrual function. 

Undereating can result in missing or irregular periods. While there is a spectrum of menstrual dysfunction that can result from undereating, the most severe is functional hypothalamic amenorrhea (FHA). This can either be primary, which means no period by 15 years of age or secondary, which is absence of 3 consecutive periods. It should be noted that if a female athlete starts to miss their period, this should not be automatically assumed to be FHA. It must be diagnosed by a health care provider after other causes of missing periods have been ruled out.

It was once thought that missing or irregular periods were due to having a body fat percentage that was too low. However, this has since been proven wrong. Some athletes will have a low body fat percentage and still have their periods, while other athletes can have a high level of body fat but be missing their periods. Later, it was thought that the stress of exercise caused missing periods. Again, this was later proven to be not true. Rather, it is insufficient calorie intake that causes FHA. When not enough calories are being consumed, the body shuts down unnecessary processes that are not critical for survival, such as the ability to have a baby. As a result, periods stop.

Unless an athlete is trying to get pregnant, the loss of a period can often be well accepted. However, irregular period should raise immediate red flags. The hormonal fluctuations that occur throughout the menstrual cycle are very important for health. In particular, the low estrogen levels that result from missing periods can have very negative health outcomes. This includes weakened bones, cardiovascular changes and even premature brain aging. It should be noted that in males athletes, rather than missing periods and low estrogen, low levels of testosterone can be seen as a result of underfuelling. This too has negative impacts on health.

When an athlete presents with missing periods, sometimes they are recommended to go on birth control pills to cause a monthly period, with the hope of protecting bone health. However, this does not fully protect against the negative health outcomes mentioned above. Furthermore, if an athlete is on birth control, they will not know if they have underlying menstrual dysfunction due to the monthly withdrawal bleed forced by birth control.

Missing or irregular periods is NOT a normal response to training or a sign that an athlete is “fit/”. If an athlete presents with this, further investigation is warranted and they should see a health care provider to rule out other causes. If deemed to be FHA, then increasing calorie intake and/or reducing exercise is needed to prevent negative health outcomes.

Categories: Megan Kuikman

Megan Kuikman

Hello! I’m Megan Kuikman. I’m a Registered Dietitian with specialized training in sports nutrition. My goal is to help athletes and active individuals achieve a healthy attitude towards health, training, and food. I empower athletes to fuel properly for training in order to restore their health and enhance performance. You can get in touch with me at:


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