Fuelling for Health and Performance

Relative Energy Deficiency in Sport (RED-S) is a common challenge in female and male athletes

On average, up to half of all athletes fail to consume enough calories to meet the body’s daily energy requirements. Most of these athletes are likely unaware of the presence and consequences of long-term under.fuelling. How do you know if you are one of these athletes, and why is adequate fuelling so important for your health and performance?

Athletes and active individuals are at a risk of low energy availability (LEA), which means that there’s not enough energy coming in through diet to cover the energy output during exercise, ultimately failing to cover the energy cost of other important body functions (reproduction and bone health, to name a few). Prolonged LEA can lead to the development of Relative Energy Deficiency in Sport (RED-S), a syndrome with a range of negative health and performance outcomes. Some of these outcomes include impaired endocrine function, bone health as well as increased illness and injury along with decreased performance. For example, research has shown that elite runners with long-term LEA are 4.5 times more likely to develop bone stress injuries than runners with optimal energy availability. In another study, female swimmers with irregular periods—a common sign of prolonged LEA—experienced an approximately 10 per cent decline in performance as opposed to an approximately eight per cent increase in performance seen in those with regular periods (and as such, optimal energy availability).

While athletes can develop LEA by restricting calorie intake (disordered eating behavior or attempts to lose body weight), it is not uncommon for athletes to experience LEA by accident. In fact, research has shown that only 25 per cent of the athletes with LEA present with disordered eating behavior. Instead, many athletes may develop LEA due to an inability or lack of knowledge to consume a sufficient amount of calories to match high training loads. This is especially common in endurance sports or team sports such as soccer, where daily energy requirements can be several thousand calories. The development of some of the health and performance impairments takes time, and often, by the time RED-S is detected, the athlete may have been experiencing LEA for several months or years. Some of the outcomes of RED-S (including decreased bone density) may be irreversible, which highlights the importance of early detection and intervention.

Due to its ability to widely affect athlete health and performance, RED-S is currently recognized as one of the biggest challenges among female and male athletes, over all ages and across all sports. While anyone can develop RED-S, females tend to be at a higher risk than males, and weight-bearing or aesthetic sports (running, triathlon, cycling, high jump and long jump, figure skating and gymnastics) tend to pose a higher risk than sports where body weight is a less important determinant of performance (team sports, field sports in track & field). Anyone involved in sports (athletes, coaches, parents, physicians, physiotherapists, etc.) can educate themselves on RED-S to prevent the development and long-term consequences of RED-S in athletes.
If you or someone you know is at risk for or experiencing symptoms of RED-S, seek help by talking to your dietitian, physician, coach or a member of your support team. Early detection and intervention are key in preventing more severe health concerns arising from prolonged LEA.


1 RED S only concerns female endurance athletes. Both females and males, across all sports, can be affected, although females in weight sensitive sports (distance running, cycling, cross country skiing, triathlon, rowing, figure skating, gymnastics, ballet) appear to be more susceptible to LEA.

2 In female athletes, missing the period is a normal sign of heavy training. Absence of three or more consecutive cycles in female athletes is a potential sign of LEA and RED S. The athlete should consult with a physician as long term amenorrhea is linked to poor bone density and subsequently, increased risk of bone stress injuries.

3 In female athletes with amenorrhea, use of hormone replacement therapy in the form of estrogen and/or progesterone pills will support bone health. Research has shown that oral contraceptive pills (a combination of estradiol and progestogen) impair the hormone insulin like growth factor 1 (IGF1, an important bone building hormone) and as such, provide no bone health benefits. Instead, transdermal 17. estradiol patches in combination with cyclic progesterone have been shown to bypass the IGF 1 route thus leading to increased bone density in individuals with menstrual dysfunction.

4 Only athletes with disordered eating can have RED S. Anyone can develop RED S even if they don t intentionally aim to create a caloric deficit. This is especially common in endurance sports or in individuals who lack knowledge to consume enough calories to manage daily caloric requirements. In fact, research has shown that appetite poorly tracks with energy expenditure when activity levels are high, which means that eating only when hungry can be problematic especially for those engaging in high levels of physical activity.

5 If an athlete is normal weight, they can t have RED S. Weight loss can indicate LEA and RED S. But you can be normal weight (or have stable body weight) and still suffer from RED S. This is because at times, the body metabolically adapts to a caloric deficit by reducing the amount of calories it expends during activity and at rest (i.e. calories in calories out). This has been shown in studies on starvation (the Minnesota Starvation Experiment) as well as weight loss research (including the 2016 paper on “The Biggest Loser).

6 A low body weight is beneficial for performance, thus mitigating the potential negative effects of RED S. While in the short term, athletes especially in weight bearing sports (running, jumping, climbing) may perform better with a lower body weight, the long term consequences of LEA and RED S are most likely to be performance hindering.


RED-S can present in many forms and symptoms can vary from one person to the next. Research is developing to confirm the best markers for identification of RED-S. Based on the current evidence, some of the indicators of RED-S are:

1 In females, absence of three or more consecutive periods (functional hypothalamic amenorrhea) or no menarche (primary amenorrhea, i.e. a female who has never menstruated) without an underlying clinical condition are often indicative of prolonged low energy availability

2 In males, blood testosterone concentrations within the lowest quartile of reference range and/or low libido can be a sign of RED-S

3 Low bone mineral density (Z score <-1.0) or frequent bone stress injuries (≥2 injuries) can be a sign of prolonged RED-S 4 Other symptoms include: decreased blood triiodothyronine (T3, a thyroid hormone 5 concentrations within lowest quartile of reference range may indicate risk), decreased resting metabolic rate, elevated total or LDL cholesterol, and low blood pressure (<90/60 mmHg)

5 Signs to look for in the field: low body weight or recent substantial weight loss (BMI <18.5 kg/ m2 or >5% weight loss in a month), increased frequency of illness/infection, poor sleep, poor mental health, unexplained fatigue, increased irritability, as well as disordered eating behaviour.

  • Note that not every athlete with RED-S will present with all these signs; instead, RED-S is likely to include a combination of indicators.

Read This Story in Our 2022 Inspiration Digital Edition

Read about Canada’s Top Fitness Trainers 2022. Need new ideas for your next workout. Test your fitness levels and see how you measure up. World-renowned breath expert, Richie Bostock shows us how to breathe correctly, 7 yoga poses for a better sleep, recipes and much more!