Dieting and Training Don't Mix

We all know fueling is a key component of marathon training and racing. I think we all can resonate with a time where we ate something and it destroyed our run or we didn’t eat enough and had to slow down. We also hear a lot of talk about racing weight which creates a lot of buzz in the running community of what to eat, how much, and when. However, sometimes well intentioned “healthy” eating or diet plans can sometimes be more dangerous then we think. In fact studies have shown 69% of women participating in weight centric sports such as running have experienced loss of menstrual function from low energy intake, while another study showed 55% of athletes studied were at risk for low energy availability.

What is RED-s?

RED-s stands for Relative Energy Deficiency in sport. RED-s in its simplest terms is when energy out is more then energy in, however energy needs are incredibly individualized based on the athletes lean body mass, exercise level, metabolic rate, stress level, etc. When the body is not receiving enough energy, hormonal, metabolic, and functional characteristics are disrupted leading to a variety of symptoms. In athletes RED-s can be seen during periods of dieting, large increase of mileage, body dissatisfaction, and underlying eating disorders. Even restricting one food group could leave a runner at great risk for developing RED-s.

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What are the consequences of RED-s?

The image above represents the simplified response when an athlete is experiencing RED-s. As you can see decreased energy, decreased sleep, and increased stressors effect the hypothalamus which is in charge of a wide array of our bodies functions including immunity, reproduction, bone density, etc. In addition to the functions of the hypothalamus RED-s can also have cardiac, GI, and development complications. Some of the most well studied consequences include decreased estrogen and testosterone in both women and men respectively. Estrogen and testosterone play a huge role in bone production and maintenance by stimulating calcium uptake and osteoclast (bone cell) function. When estrogen and testosterone are low, athletes are at risk for decreased bone density, increasing their risk of injuries, especially stress fractures ( and we all know injuries are no fun)! Other signs and symptoms include: decreased muscle strength, increased irritability, depression, impaired judgement, decreased concentration, decreased coordination, and decreased training response.


Treatment and action

If you think you or your running buddy could be experiencing RED-s, you should reach out to a dietitian to ensure you are meeting your energy needs. Treatment plans including increasing energy intake, decreasing exercise, supplementing vitamins, increasing strength training, etc. This is especially important if an athlete has lost or had irregular menstrual function, putting an athlete at great risk for further complications.

If you have any questions or concerns you reach out to Sydney Benator, RD, LD at


Mountjoy M, et al. Br J Sports Med 2018;52:687–697. doi:10.1136/bjsports-2018-099193

Br J Sports Med 2015;49:421–423. doi:10.1136/bjsports-2014-094559

Keay, N. 2018 Update: Relative Energy Deficiency in Sport Blog British Journal of Sports Medicine