Get access to everything we publish when you sign up for Outside+.
It used to be called the female athlete triad: a condition characterized by lost menstrual periods, a decline in bone density, and stress fractures resulting from taking in too few calories. For years, the condition was regarded as a concern only for women—and only those who lost their periods. Women who retained their periods weren’t considered at risk, and men, whose hormone systems are different, were thought to be unaffected.
In 2014, after an extensive review of the medical literature, the International Olympic Committee officially renamed the condition RED-S (relative energy deficiency in sport) and expanded the definition to recognize that the basic problem is consuming too few calories to support everything your body needs to do—a problem that is broader than the traditional female triad and can affect men as well as women.
When it’s not actively training, the body’s energy balance is skewed heavily toward things other than exercise. The brain needs about 20 percent of the average person’s overall caloric intake. The liver needs about the same amount. Lesser amounts go to the heart, kidneys, and other organs required to keep you alive and functioning. For nonathletes, the muscles are relatively minor contenders in this competition, requiring a mere 20 percent of total energy intake.
For athletes, of course, the muscle demands are much higher. But as long as you eat enough, everything stays in balance. The problem comes if you try to lose weight or simply try too hard to retain a lean body mass. When that happens, says Lewis Halsey, an environmental physiologist at the University of Roehampton, London, you encounter a mysterious aspect of human physiology known as energy compensation. “Put simply,” he says, “our bodies partially compensate by cutting energy spent on other things.”
We are designed to survive; when faced with what is perceived as starvation, our bodies will find ways to offset it. This compensation, Halsey says, includes “shutting down in a desperate attempt to limit how far negative you go.” That is RED-S in a nutshell.
The focus was initially on women because women had an obvious sign in the loss of their periods, says Nicky Keay, an exercise endocrinologist at University College London and Durham University. “We now have clear evidence that men should pay attention.”
In one study, for example, Keay examined 50 competitive male cyclists: four competing internationally, 20 nationally, and the rest at the regional level. She then gave them a questionnaire and a clinical office visit, designed to identify those whose eating habits were restrictive enough to put them in a category she described as “low energy availability.” This evaluation was cycling-specific, but the basic questions were ones that other athletes can also relate to, such as average weekly training volume (including cross-training), how often they trained in a fasted state, history of intentional weight loss, how they fueled for workouts lasting more than an hour, what they ate afterward, and other questions about training and diet.
The results were eye-popping. Those whose training and dietary patterns appeared to be insufficient had substantially lower bone density and testosterone than would be expected for men of their age. There was also an effect on athletic performance. “Those athletes judged to be in low energy availability didn’t do as well,” Keay says. In 60-minute time trials comparing average power output—calculated in watts per kilogram, which theoretically would give an advantage to lighter cyclists—the athletes showing signs of RED-S scored worse.
Kathy Butler, the coach of Run Boulder Athletic Club and the head of USA Track and Field coaching instruction, says that RED-S can harm health in many other wide-ranging ways beyond reduced bone mineral density, including negative effects on the immune system, heart, mood, coordination, glycogen supply, and thyroid level. Athletes should also note that protein synthesis takes energy. If that’s in short supply, the body may not only be unable to rebuild stronger after a workout, but may also struggle to recover at all. One of the possible effects of RED-S, Butler says, is a reduction in muscle strength.
These findings are not restricted to top competitors, says Keay. “A lot of people have the perception that only elite athletes get this,” she says. “But I would say it’s more like non-elite aspiring amateurs.” Elites are susceptible but often surrounded by teams of doctors, coaches, nutritionists, and other experts who can spot incipient problems. “Whereas if you’re a well-intentioned amateur, you don’t have the backup, so it’s easy to misjudge things,” Keay says.
In male athletes, recognizing the signs of RED-S can be a lot more difficult than it is for women. It’s usually diagnosed via a battery of blood tests, but there are also symptoms athletes can recognize on their own. Fatigue not explained by something obvious, like lack of sleep or increased stress, is an important marker, Butler says, as are repeated injuries or illnesses. Keay adds low libido to the list, or just a general lack of energy and enthusiasm. Poor sleep and digestive troubles may also be signs of RED-S.
While a restricted diet is the cause of RED-S, it isn’t necessarily linked to being too thin, Keay says. People with RED-S may not look underweight and may not seem to have a problem.
The solution, she says, is to trust that millions of years of evolution have programmed your body to perform at its best if you give it what it needs. If you artificially restrict it in an effort to attain some hypothetical ideal racing weight, “the body will get scared,” Keay says. It will go into energy-saving mode, and both your overall health and your performance will suffer.
Butler says the solution may be as simple as the oft-stated advice to consume about 300 calories’ worth of food or drink as soon as possible after training. Studies have indicated that waiting too long between meals or snacks can put your body into an off-and-on starvation mode it would not otherwise encounter. Simply changing the timing of when you eat to ensure that you get what you need when you need it may be all it takes to kick it out of that mode and into a healthy state.
It’s important not to let this post-training fuel replace your normal mealtime intake. If you do that, your total calories may still be too low. And, Butler points out, failing to refuel by as little as 300 calories a day is the equivalent of losing an entire month’s worth of food over the course of a year.
If all of that seems somewhat vague and complex, it is. Nutritional problems are seldom simple. What is simple is the bottom line: men are just as much at risk of having energy-deficiency issues as women, even if the symptoms aren’t as obvious. If your health, performance, mood, or overall energy is in decline and you’re strongly focused on weight or diet, the answer may be that you have overly restricted calories and need to relax. Shift your eating patterns to get a snack soon after workouts, or add an energy bar or two to your normal diet. And if you’re not sure how best to do that, consult a nutritionist.