RELATIVE ENERGY DEFICIENCY IN SPORT (REDs) Q&A: WHAT IT IS AND HOW TO PREVENT IT

1. What is REDs? How is it different from the female athlete triad and overtraining?

REDs (Relative Energy Deficiency in Sport) occurs when an athlete does not take in enough energy (calories) to support both their training and their basic physiological functions. This creates low energy availability, which can result from factors like increased training without increased fueling, nutrition misinformation, disordered eating or eating disorders, and body image concerns. 

REDs can impair multiple body systems, including growth and development, reproductive health (missed or irregular periods, low libido), bone health (stress fractures, early osteoporosis), immunity (frequent illness, slow healing), metabolism and digestion (gastroparesis, cramping, alterations in bowel habits), cardiovascular health (low heart rate, dizziness, potential long-term heart damage), and mental health (depression, anxiety, irritability, and reduced cognitive function). Additionally, it has negative effects on athletic performance including decreased endurance, decreased power, delayed recovery, poor training adaptations, and decreased motivation. The graphics below are from the updated 2023 IOC Consensus Statement on REDs and detail the plethora of physiological and performance based consequences of REDs.

The Female Athlete Triad is a narrower, older model that focuses on three issues in female athletes: low energy availability (with or without disordered eating), menstrual dysfunction (irregular periods or amenorrhea) and low bone density (osteopenia or osteoporosis). REDs is the updated, broader framework released by the International Olympic Committee in 2014 (updated in 2018 and 2023) that applies to all genders and includes many more health and performance effects. 

Overtraining and REDs look very similar and have a lot of symptomatic overlap, but they are not the same thing. Overtraining syndrome is traditionally described as a chronic imbalance between intense training load and insufficient recovery. It predominantly affects the central nervous system and it can be difficult to diagnose because there are few clear biomarkers. However, research has shown that most athletes labeled as “overtrained” may also be underfueling. In fact, in over 80% of studies on overtraining, athletes had low energy or low carbohydrate availability during periods of performance decline, producing the same hormonal, immune, and recovery problems seen in REDs. This means many cases of “overtraining syndrome” could actually be misdiagnosed REDs where the body is not breaking down from too much training, but from too little fuel to support the training. 

2. Can REDs occur in recreational and professional athletes? Is it more common in

recreational or professional athletes?

REDs can absolutely occur in both recreational and professional athletes. I would argue that REDs is likely more common in recreational athletes than in professional athletes. While elite athletes may train more and/or at higher relative intensities, they also usually have access to sports dietitians, medical teams, and structured fueling and training plans. Recreational and sub-elite athletes, on the other hand, often train just as hard (comparatively) while juggling full-time jobs, family, and limited nutrition/medical support. This means they are more likely to underfuel, follow misinformation, or unintentionally restrict intake, which makes REDs both more common and more likely to go undiagnosed in this group.

3. What are warning signs of REDs; does REDs manifest differently or similarly depending on the individual?

Warning signs of REDs include persistent fatigue, declining performance despite consistent training, frequent illness or injury (specifically bone stress injuries), missed or irregular periods, gastrointestinal issues such as delayed gastric emptying/bloating/changes in bowel habits, low libido/lack of morning erection, mood changes, poor recovery, gastrointestinal issues, sleep disturbances, mood/cognition changes, and feeling cold, weak, or “flat” in workouts.

REDs does not look the same in everyone. It can affect athletes of any gender, body size, or sport, and symptoms vary depending on genetics, hormones, training load, stress, and how long/to what degree underfueling has been present. Some athletes may present with obvious red flags quickly like missed periods or stress fractures, while others may only notice subtle performance declines or changes in mood and recovery for a while before more alarming symptoms arise.

4. Are women or men more susceptible? Is REDs in women and men manifested

differently?

While REDs affects both men and women, most research has historically focused on female athletes because females have higher rates of REDs. The research community continues to emphasize the need for more studies on REDs and low energy availability in men. Interestingly, current evidence suggests that women may experience symptoms when energy availability drops below 30 kcal/kg fat-free mass/day, while men can often sustain lower levels (~9-25 kcal/kg fat-free mass/day) before symptoms arise. Low energy availability in men can still disrupt hormones, metabolism, immunity, bone health, performance, and lean body mass. Emerging signs in men include low libido and fewer morning erections. Overall, the physiological impacts of REDs are similar across sexes, though the exact thresholds and severity of symptoms can differ. 

5. Does age impact the susceptibility to REDs?

Yes, age can impact susceptibility to REDs. Younger athletes, especially adolescents, are at higher risk because their bodies are still growing and require significantly more energy for development and puberty in addition to training. Low energy availability during these years can more quickly disrupt hormones, bone mineralization, and overall growth. In fact, the consequences of underfueling in adolescents are particularly striking as up to 90% of bone mass is formed by age 18, and some effects on bone health may never fully resolve depending on the severity and duration of REDs during adolescence. 

Adult athletes can also develop REDs, and while their growth is complete, underfueling can still negatively affect hormone balance, bone density, metabolism, immunity, mental health, recovery, and performance. Even temporary periods of low energy availability can lead to fatigue, increased injury risk, or slower training adaptations, making early detection and correction essential for long-term health and athletic performance.

6. How does someone recover from REDs?

Recovery from REDs requires a comprehensive, individualized approach. The primary goal is to restore adequate energy availability through changes to diet and training that ensure athletes get in enough calories, carbohydrates and other nutrients consistently throughout the day to support health and performance. Some cases may also require weight restoration (particularly women with secondary hypothalamic amenorrhea) and targeted treatment for specific health issues such as low bone density, gastrointestinal symptoms, or mood disturbances. A multidisciplinary team including sports dietitians, sports medicine physicians, psychologists, therapists, coaches and even family is essential, especially if disordered eating is present. Treatment can take time because different symptoms improve at different rates, and progress can be slowed by the psychological and emotional challenges that often accompany disordered eating. Building healthy fueling habits, restoring energy availability, and addressing body image or eating-related behaviors requires patience, support, and consistent guidance from the treatment team. The overall goal is to safely return athletes to full participation while addressing both the causes and consequences of low energy availability.

7. How can you prevent REDs?

Primary prevention of REDs starts with education and awareness. Many athletes, coaches, parents and even healthcare professionals have limited knowledge of REDs. Short-term education programs that teach about energy availability, disordered eating behaviors, and body image have been shown to improve nutrition knowledge and reduce unhealthy dieting or body concerns in both male and female athletes. However, more research is needed to develop and validate REDs specific education and prevention programs for athletes. Social media also plays a role: athletes and their support teams should be encouraged to critically evaluate online nutrition advice, avoid diet or body-focused content that promotes unhealthy behaviors, and follow credible, evidence-based sources. Secondary prevention involves identifying and moderating progression of REDS through screening tools like the REDS CAT2 LEAF-Q, DESA-6, EDE-Q etc, health interviews, and biomarker assessments can also help catch and treat REDs before it causes serious problems.

8. Lately, there has been significant focus on the importance of properly fueling workouts. What is the influence of intra workout fueling and the development of REDs? And does the type of fuel (i.e. carbohydrates, fats, protein) I use during training matter?

Intra-workout fueling plays a critical role in REDs prevention because it helps reduce “within-day energy deficits.” This refers to spending long periods of the day in a net negative energy balance, even if total daily caloric intake is adequate. Research shows that even relatively small within-day deficits (~300 to 400 kcal) can disrupt hormones, bone health, and metabolism in ways similar to low energy availability and REDs. While it’s impossible to avoid all energy dips, we can minimize how large and how long they are, and that’s where fueling before, during, and after training matters.

The biggest gap for most athletes is carbohydrates. Training can drive needs anywhere from 5 - 12 g/kg/day, which is far higher than most people meet by hunger alone. Without intentional carbohydrate planning and ensuring adequate intra workout carbohydrate intake, athletes are at high risk for low energy availability, low carbohydrate availability, and within-day deficits, all key contributors to REDs.

This is why nutrient timing is just as important as total intake. Athletes should avoid fasted training and instead aim to fuel with easily digestible carbohydrates before and during exercise to keep energy availability high while the body is under the greatest physiological stress.

The type of fuel matters. Before and during training, the priority should be simple, rapidly absorbed carbohydrates - low fiber, low fat, and low protein - to provide fast energy and minimize GI distress. Protein and fat generally do not meaningfully support training performance or REDs prevention during most workouts. The main exception is ultra-endurance events (>6 hours), where small amounts of fat and protein from real foods can help with satiety, palatability, and meeting very high energy needs while preventing excessive muscle breakdown.

Evidence-based carbohydrate targets during training are:

• <2.5 hours: 40–60 g/hr (single-source carbs, ie glucose or maltodextrin)

• 2.5 - 5 hours: 60–90 g/hr (multiple transportable carbs such as glucose + fructose in ~2:1 ratio)

• >5 hours: 60–90+ g/hr using multiple transportable carbs (2:1 glucose:fructose (60g/hr) or ~0.8:1 glucose:fructose (>90g/hr)), with small amounts of real food throughout for palatability and variety

Post-workout, if a full meal isn’t immediately available, a 3:1 carbohydrate-to-protein recovery snack within 30-60 minutes supports glycogen repletion, muscle repair, and restoration of energy availability. Fluids and electrolytes are also essential, especially for heavy or salty sweaters and in hot or humid conditions. 

In short: fueling during training is foundational for protecting hormones, bones, metabolism, and performance. Eat all the carbs. Crush all your goals. 👏

Sources: 

Mountjoy M, Ackerman KE, Bailey DM, Burke LM, Constantini N, Hackney AC, Heikura IA, Melin A, Pensgaard AM, Stellingwerff T, Sundgot-Borgen J, Torstveit MK, Jacobsen AU, Verhagen E, Budgett R, Engebretsen L, Erdener U. International Olympic Committee (IOC) consensus statement on Relative Energy Deficiency in Sport (RED-S). Br J Sports Med. 2023. doi: 10.1136/bjsports-2023-106994.

Stellingwerff T, Heikura IA, Meeusen R, Bermon S, Seiler S, Mountjoy ML, Burke LM. Overtraining Syndrome (OTS) and Relative Energy Deficiency in Sport (RED-S): Shared Pathways, Symptoms and Complexities. Sports Med. 2021 Nov;51(11):2251-2280. doi: 10.1007/s40279-021-01491-0. Epub 2021 Jun 28. PMID: 34181189.

Cabre HE, Moore SR, Smith-Ryan AE, Hackney AC. Relative Energy Deficiency in Sport (RED-S): Scientific, Clinical, and Practical Implications for the Female Athlete. Dtsch Z Sportmed. 2022;73(7):225-234. doi: 10.5960/dzsm.2022.546. Epub 2022 Nov 1. PMID: 36479178; PMCID: PMC9724109.