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8 min read<\/p>\n8 min read<\/p>\n
When it comes to exercise, there\u2019s one thing that\u2019s just as important as the training itself: fueling. Having the right nutrients\u2014and enough calories\u2014to sustain your activity and recover from it are critical for staying healthy, feeling your best, and keeping your body functioning in tip-top shape. After all, fueling your body isn’t just about performing well today; it’s about being able to keep doing what you love for years to come.<\/p>\n
Eating can sometimes feel like an afterthought, especially when you\u2019re busy with training, but consistently underfueling can actually result in a condition called relative energy deficiency in sport, or RED-S for short. And women have a much higher risk of developing RED-S compared to men. In a 2026 study in the Journal of Science and Medicine in Sport<\/a>, researchers found that 70 percent of high-level female athletes were at risk of developing RED-S.<\/p>\n Top-ranked tennis player Emma Navarro<\/a> recently revealed that she is one of those athletes dealing with the condition. Earlier this month, she posted on Instagram, detailing her experience, which included extreme mood swings, brain fog, a weakened immune system, constant headaches, and bouts of dizziness. Exercises she could do with ease in the past suddenly felt impossible. She was also hungry, all the time. \u201cI had been under-fueling for almost three years,\u201d she wrote. \u201cMy body was fighting back any way it knew how.\u201d<\/p>\n But, you don\u2019t need to be an elite-level tennis player to experience the condition. Here\u2019s what you need to know about RED-S, including how to spot\u2014and stop\u2014it early, according to experts.<\/p>\n Meet the experts: Elizabeth Matzkin, MD<\/a>, is an orthopedic surgeon and chief of women\u2019s sports medicine at Brigham and Women\u2019s Hospital. Amy West, MD<\/a>, is a sports medicine physician at Northwell Orthopedic Institute. Amy Stephens, RD<\/a>, is a sports dietitian who specializes in eating disorders.<\/p>\n What Is RED-S?<\/p>\n There\u2019s a simple explanation behind what causes RED-S: It occurs when someone is not eating enough to meet the demands of their training\u2014or even their body\u2019s basic physiologic needs, says Elizabeth Matzkin, MD, an orthopedic surgeon and chief of women\u2019s sports medicine at Brigham and Women\u2019s Hospital. Your body needs energy not only to sustain you, say, on a run or in a weightlifting session, but it also needs energy to support bone health<\/a>, hormone production<\/a>, metabolism<\/a>, immune function, and cardiovascular health<\/a>.<\/p>\n When you\u2019re consistently not consuming enough food to support your activity levels, over time, your body won\u2019t have the energy it needs to support those critical functions, leading to a wide range of symptoms that define RED-S\u2014which is more than medical jargon for undereating. It reflects what happens when your body is chronically underfueled and can lead to long-term health issues.<\/p>\n Anyone, from the elite athlete to someone training for their first half-marathon to the person increasing their lifting sessions in the gym while trying to lose weight, can be at risk of developing RED-S. Remember, the \u201cr\u201d in RED-S stands for relative; so it\u2019s all about not meeting your energy needs, whatever they are.<\/p>\n When underfueling, in the short term, you may experience fatigue, impaired concentration, more frequent illnesses, poor recovery, and irregular periods or none at all, Dr. Matzkin says. When it comes to your sport, training and performance may suffer too. Low energy availability can make it harder to sustain a workout, decrease strength and endurance, or lead to muscle weakness or pain, says Amy West, MD<\/a>, a sports medicine physician at Northwell Orthopedic Institute.<\/p>\n You\u2019ll also be much more susceptible to injuries, particularly when it comes to your bones. This has impacts on the long term: \u201cAdolescence and young adulthood are critical years for building peak bone mass, so prolonged low energy availability during this period may have consequences later in life,\u201d Dr. Matzkin says. Down the line, that could mean osteoporosis. Meanwhile, missing your period for long periods of time can have impacts on future fertility, Dr. West adds.<\/p>\n Early stages of RED-S can happen pretty quickly, says Amy Stephens, RD<\/a>, a sports dietitian who specializes in eating disorders. After just one day of underfueling, you\u2019ll feel symptoms of \u201changer\u201d; after just a week, your body may stop building muscle and endurance. Then, she says, it could take six to nine months to fully recover.<\/p>\n Why Is RED-S More Common in Women?<\/p>\n RED-S is much more associated with women and girls compared to boys and men. Until 2014, RED-S was referred to as the \u201cfemale athlete triad,\u201d<\/a> which highlighted the relationship between undereating, menstrual dysfunction, and decreased bone mineral density. While RED-S can happen to anyone, \u201cfemale athletes are more vulnerable, especially in sports that emphasize leanness, endurance, aesthetics, or weight categories,\u201d Dr. Matzkin says. (Think: Running, gymnastics, and diving.)<\/p>\n But, that\u2019s not the only reason women may deal with RED-S more than men. There\u2019s also the pressures that women face disproportionately to be thin<\/a>, says Dr. West, and the fact that women are more likely to have eating disorders.<\/p>\n Signs of RED-S to Watch Out For<\/p>\n RED-S doesn\u2019t happen all at once. Earlier, more subtle signs like fatigue and trouble sleeping<\/a> pop up when a person has what docs call low energy availability, which occurs when they\u2019re not eating enough to support their activity levels. As someone is continuously in a state of low energy availability, RED-S can occur.<\/p>\n Low energy availability and RED-S can affect almost every system in the body, but these are the areas you may most often see symptoms, according to the doctors.<\/p>\n Earlier signs include:<\/p>\n Persistent fatigueTaking longer to recover after a workoutDeclining performanceGetting sick more oftenPoor sleepIncreased hungerMood swings and\/or increased anxiety and depressionHair lossWeight loss<\/p>\n More serious red flags include:<\/p>\n Irregular or absent periodsPain when putting weight on a limbFrequent injuries, especially recurrent stress reactions or stress fracturesHow to Make Sure You’re Eating Enough for Your Activity Level<\/p>\n
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