REDs in Athletes: Signs of Underfueling and How to Recover

Frequent injuries, fatigue and slow recovery may be signs of relative energy deficiency in sport (REDs). Learn how underfueling affects athletic performance and what athletes, parents and coaches should know.

On any given day, as Director of Olympic Sports Nutrition for the University of Miami Hurricanes, Maryellen Carrigan, R.D.N., works with at least one athlete dealing with an injury or slow recovery due to poor nutrition. The syndrome, known as relative energy deficiency in sport (REDs), is common among young elite athletes, particularly runners, dancers and gymnasts.

Of the 300 Canes athletes in every sport besides football that Carrigan’s sports nutrition team oversees, there are typically at least 10 to 15 dealing with REDs.

“If an athlete isn’t progressing in their sport the way we might expect them to, has a persistent injury that’s not healing or is sick all the time from a weakened immune system, they get referred to sports nutrition to see if they’re underfueling,” says Carrigan.

What is REDs?

The International Olympic Committee (IOC) defines REDs as impaired physiological and/or psychological functioning caused by exposure to prolonged or severe problematic low energy availability.

Simply put, athletes who expend more energy than they replace over time start to fall apart. They’re tired, underperform, are more prone to injury, get sick more often and take a longer time than usual to recover.

If that energy mismatch goes on too long, especially in teens and young adults, REDs can affect the metabolism, reproductive function, musculoskeletal health, immunity and cardiovascular and blood health.

The IOC first introduced the concept of REDs in 2014, recognizing a range of potential health and performance consequences in both female and male athletes. The sports medicine community has moved beyond the older concept of the “female athlete triad,” which focused on energy availability, menstrual function and bone health in female athletes.

REDs affects all types of athletes and body types

REDs isn’t exclusive to runners, but it’s common enough that the sport has the most education and knowledge of the disorder. REDs has also received broader attention through the experiences of elite athletes. In her 2026 memoir, This Is Not About Running, former professional runner Mary Cain describes being pressured to lose weight while training with the Nike Oregon Project and experiencing repeated injuries and other health problems.

Carrigan says her team is seeing REDs across sports, in both male and female athletes and across body types. “Being lean or underweight doesn’t necessarily mean you’re underfueled, and having a bigger body does not mean you can’t possibly underfuel as well.”

Serious amateur athletes are at risk for REDs, too, and are less likely to speak with a provider about sports nutrition. For example, long training runs for a half or full marathon without enough fuel to recover put you at risk for REDs.

Signs a young athlete might have REDs

Student-athletes at UM are usually identified as possibly having REDs by a sport orthopedist, a strength coach, athletic trainers or a physical therapist.

Common symptoms of underfueling that can lead to REDs include:

• A persistent injury
• Multiple injuries in different areas, such as stress fractures
• Poor recovery
• Weakened immune system
• Hypothyroid condition
• Exhaustion
• Failure to meet training goals
• Lack of menses in female athletes

All the symptoms of REDs can, of course, have other causes, but Carrigan recommends parents, coaches and providers ask about nutrition when these symptoms appear.

“A stress fracture is a massive red flag for nutrition-related injury, as is a slow recovery,” she says. “A bone takes a lot of energy to heal. It’s very easy in these athletes to be underfueling for what that bone needs to rebuild when you’re injured.”

Quick facts about fueling for sports every parent and coach should know

There’s no one formula for how much an elite athlete should eat to fuel their body for their sport. “Every athlete has a different body composition, metabolism, genetics and muscle mass. It’s difficult for our student-athletes to hear they need to double what they’re eating compared to another teammate,” says Carrigan.

Use analogies when food and weight are sensitive topics

Carrigan finds helping athletes understand fueling is easier when she uses a different analogy, such as a bank account or a gas tank. “Your workout is a withdrawal, so you need to eat food to put money back in. If a workout is longer or harder, it’s a greater withdrawal.”

Athletes tend to understand nutrition better when they think about avoiding a $0 bank balance or an empty gas tank. “The negative compounds over time, so that’s usually what we see in REDs,” she says.

Unintentional underfueling is common

REDs isn’t synonymous with an eating disorder, nor does underfueling always happen intentionally. Carrigan sees athletes who believe they’re eating reasonably well and aren’t deliberately skipping meals or snacks.

“It’s not just, like, you underate today. The problem is when the amount of energy you’re putting back in may not match the amount your body needs,” she says.

Carbohydrates are king for athletes

Carrigan’s team does a lot of coaching around carbohydrates as fuel for sports. Athletes often eat too few carbs and are even afraid of overeating them. “We do a lot of reeducating that carbs equal sports performance,” says Carrigan.

Small fueling changes can lead to meaningful wins

When athletes fear gaining weight from eating more, Carrigan recommends starting small instead of asking them to double their calories, for example. Encourage eating a granola bar or sandwich before a workout and the athlete will see it did no harm and likely made the workout easier. “You need to build some trust before you can totally change a young person’s diet,” says Carrigan.

The good news is that Carrigan finds most athletes recover well from REDs once they understand how much fuel their body needs to perform. “Ultimately, we can coach a lot of our athletes out of this kind of cycle,” she says.

Written by Wendy Margolin. Reviewed by Maryellen Carrigan, R.D.N.

Tags: REDs in athletes, REDs recovery, REDs symptoms, relative energy deficiency in sport symptoms, signs of underfueling, sports nutrition, underfueling in athletes