For athletes, performance and endurance are often the top priorities. But what happens when the body doesn’t get enough fuel to sustain both training and essential bodily functions? This is where RED-S, or Relative Energy Deficiency in Sport, becomes a critical issue.
In a recent podcast episode, we spoke with Tina Goršek Šparovec, a nutritionist and researcher on a mission to educate coaches and athletes about this condition and ultimately optimize training sessions.
What Is RED-S?
RED-S occurs when an athlete consistently fails to consume enough energy to support both their training and basic bodily functions. When this energy deficit persists, the body prioritizes essential functions for survival and shuts down or adapts others, leading to a range of health issues.
Not Just a Female Problem
RED-S was originally called the Female Athlete Triad because it was first recognized in female athletes who experienced three interconnected issues:
- Low Energy Availability – With or without an eating disorder.
- Menstrual Dysfunction – Irregular or absent menstrual cycles (amenorrhea) caused by hormonal imbalances.
- Low Bone Mineral Density – Increased risk of stress fractures and early-onset osteoporosis due to insufficient energy and hormonal disruptions.
For a long time, this condition was thought to only affect women because menstrual irregularities were one of the most visible warning signs.
However, we now know that RED-S has many other health consequences, and male athletes can also get RED-S. This broader understanding led to the condition being renamed Relative Energy Deficiency in Sport (RED-S) to reflect that it affects all athletes, regardless of gender.
Consequences of RED-S
RED-S has wide-ranging health consequences including bones, immune function, digestion, and more.
If left untreated, RED-S can have lifelong consequences. One of the most serious risks is reduced bone density, which can lead to osteoporosis at an early age. “It can be life-changing to have the bone mineral density of an 80-year-old at 25,” warns Tina.
Common symptoms of RED-S include:
- Loss of menstruation (in female athletes)
- Loss of morning erections (in male athletes)
- Sleep disturbances
- Reduced libido
- Frequent injuries, especially stress fractures
- Persistent fatigue
- Decreased immunity (frequent colds or illnesses)
- Digestive issues (constipation, bloating, or discomfort)
- Mood swings, depression, or anxiety
- Declining athletic performance or motivation
A drop in motivation for training can be a warning sign of RED-S.
What Causes RED-S?
RED-S is caused by chronic under fueling. More specifically, RED-S is caused by not eating enough carbohydrates. Research shows that replacing calories from carbohydrates with calories from fats or protein will not prevent RED-S: the body needs carbohydrates for fuel.
Tina explains why:
Eating carbohydrates during or after training causes insulin levels to rise and signals to the body that there’s enough energy available. This doesn’t happen if you eat something like nuts instead of carbohydrates. The body will think it is still in an undernourished state and the body will remain under the influence of stress hormones for a longer period.
Athletes must consume carbohydrates to meet their high energy needs.
How Many Athletes Have RED-S?
Tina says that, considering that the absence of menstruation with runners is more than 50%, many athletes likely have RED-S. In sports like gymnastics, dance, and track and field, the prevalence is likely higher because the need for those athletes need to have a lower body mass is higher.
However, many of these athletes aren’t aware that they have RED-S, and diagnosing it can be difficult.
RED-S is also prevalent among top-level athletes.
Challenge of Diagnosing RED-S
Identifying RED-S can be challenging, especially because athletes tend to normalize symptoms like fatigue and performance fluctuations. And, as Tina said, many doctors won’t come to the conclusion that a loss of morning erection is a consequence of too much sport.
Even “obvious” symptoms like amenorrhea (lack of menstruation) can go overlooked. While more gynecologists are becoming aware of the condition, Tina says many still think amenorrhea is a minor issue. Instead of addressing the root cause—chronic under fueling—they often prescribe hormone replacement therapy as solution. This only masks the problem.
Further, there is a prevalent mentality that athletes need to suffer to achieve results. Tina is adamant that this needs to be addressed—especially with amateur athletes who don’t have such clear boundaries between everyday life and training.
Can You Have RED-S Without Losing Weight?
Yes. Tina points out that the body can adapt to chronic energy deficiency by reducing its metabolic rate to conserve energy. This can keep body weight stable even when under fueling. Additionally, fluid retention can mask weight loss. Therefore, relying solely on body weight as an indicator of energy balance is misleading.
Likewise, you can get RED-S if you eat a lot.
Tina points out that it takes 16 to 36 hours to replenish glycogen stores. Athletes who don’t eat regularly or practice intermittent fasting won’t be able to replenish their glycogen stores.
This is especially true of endurance athletes because they require high levels of energy for extended periods of time. If they don’t eat before, during and after training, they can end up in a chronic energy deficit.
It is important to consume carbohydrates after exercise.
How to Treat RED-S
The primary treatment for RED-S is to restore proper energy balance. This means eating more (particularly carbohydrates) and training less.
Tina says athletes with RED-S may need to take a complete break from training, and slowly start to come back. It could take 6 to 12 months to get back to normal training.
Successful athletes pay a lot of attention to proper nutrition.
The Role of Coaches, Nutritionists, and Medical Professionals
As Tina pointed out, addressing RED-S effectively requires a coordinated approach between different health professionals. Unfortunately, treatment for RED-S is often fragmented.
A doctor may refer an athlete to an endocrinologist, a gynecologist may prescribe pills, but rarely does the athlete receive direct guidance from a nutritionist who can help them correct their energy balance. Pills are not the solution—comprehensive treatment is needed.