top of page
  • Writer's pictureNina Crowhurst

Are you eating enough? A guide to Relative Energy Deficiency in Sport.

In a nutshell, food is required for your body to fuel exercise and a range of issues can result if intake is insufficient. Theoretically this seems like common sense, but in the performance driven sporting world ensuring adequate intake is not so simple. Do you find you get injured frequently? Are you often sick or experience other health issues? Do you have difficulty recovering from training sessions or achieving the results you should? If any of this sounds familiar a thorough review of your nutrition may be indicated.

Relative Energy Deficiency in Sport (RED-S) is a state in which the normal physiological processes of an athlete’s body are impaired due to a lack of energy availability. Put simply, the athlete is not achieving sufficient calorie intake (food) to sustain both the sporting demands placed on the body and its basic functions. This results in short and long term negative effects on overall health and performance.

From a Physiotherapy perspective, RED-S is often a factor in bone stress injuries and incidence of RED-S can be high in certain sports. Early identification of athletes at risk of RED-S is vital as some effects of RED-S may be irreversible. Treatment of injury and return to sport is reliant on adequate energy for the healing process to occur. Read on as to explore RED-S and the effects it can have on health and injury.

Health Consequences of Relative Energy Deficiency in Sport (RED-S). Mountjoy et al (2018)


What is Energy Availability?

Energy Availability is a state in which the athlete’s energy intake (food) exceeds the energy demands of exercise performed and leaves sufficient energy for the body to maintain optimal health and performance (Mountjoy et al 2018). Energy availability (EA) is calculated as:

Low Energy Availability occurs when an athlete is not consuming sufficient energy intake (food) to fulfil their sporting demands as well as normal physiological body functions. This can occur either through decreased food intake or increased energy expenditure. If this state is maintained, health related effects may develop known as Relative Energy Deficiency in Sport (RED-S). The infographic below nicely demonstrates Low Energy Availability and how it may occur intentionally or unintentionally.

Research has shown that to maintain healthy functioning of the body, females require

45 kcal/kg Fat Free Mass/day. Significant negative effects on bodily functions occur when dropping closer to 30 kcal/kg Fat Free Mass/day. Fat Free Mass must be calculated via Dexa Scan for this calculation to be accurate. The exact energy requirements for male athletes have not yet been established.

Who is at Risk of Developing RED-S?

Female athletes are generally at greater risk of developing RED-S although research is increasingly showing male athletes can also be affected. High risk sports are those in which lighter body weight or leanness is advantageous. The advantages of lighter weight may be in performance, appearance or to meet competition weight categories. In such sports the incidence of RED-S is equal across male and female athletes.

Endurance sports have greater potential for RED-S given the high Exercise Energy Expenditure of the sports. This is particularly so if changes in volume and intensity are made without accompanying nutrition changes. Examples of when this may occur include entering pre-season training, changing from training to competition phases or during intense training blocks/camps without specifically calculated and adjusted changes in nutritional requirements.

RED-S may also develop due to inadequate food availability – quantity or type of food. This can be a factor in food intolerances/preferences, fussy eaters and when travelling. The cost of food and financial constraints may also contribute. Athletes with Disordered Eating or Eating Disorders are also at risk and it should be noted that prevalence of these is higher in weight-sensitive sports.

A study by Ackerman et al (2018) found that almost 50% of a group of 1000 female athletes aged 15 – 30 presenting to a Sports Medicine Clinic for health or injury assessment had Low Energy Availability. Further, those with Low Energy Availability had a higher BMI than those with adequate Energy Availability. Therefore, it is important to note that judgement of energy intake via body composition does not always identify athletes with issues.


What Effects does Low Energy Availability have on the body?

(Keay and Rankin 2019).

The effects of Low Energy Availability are numerous and complex. As an overall summary:

· Bone Health

Low Energy Availability negatively affects bone turnover in females and some males. This predisposes athletes to bone stress injuries such as stress reactions/fractures and in the long term can result in Low Bone Mineral Density. If this occurs in the peak bone mass development stages at ~ 20 years of age, lifelong irreversible changes in bone density and bone strength may occur. Osteopenia and Osteoporosis can result in later years. Jockeys, Runners, Swimmers and Cyclists of both sexes have an increased risk for lower Bone Mineral Density. Previous bone stress injury is one of the biggest risk factors for further bony injury and can be a cause of repeated injury despite good biomechanics, appropriate training load etc.

· Menstrual

Low energy availability causes disruption in reproductive hormones and for female athletes this can disrupt the normal menstrual cycle. This may present in younger athletes not getting their period (Primary Amenorrhoea); a sustained loss of period for more than three consecutive cycles (Secondary Amenorrhoea); or increased cycle length of more than 45 days (Oligomenorrhoea). More subtle menstrual dysfunction such as changes in cycle duration or flow can also occur from inadequate nutrition.

Normal hormone levels of Oestrogen and Progesterone are vital for bone health. Alterations in these levels, such as in menstrual dysfunction, will independently result in negative bone changes. When these changes are combined with the further Low Bone Mineral Density effects of Low Energy Availability, the risk of bone stress injury is significantly increased.

Maintenance of a normal menstrual cycle is vital for female athlete health and cycle monitoring can provide valuable information of how the body is handling training loads. It is important to note that the use of a Hormonal Based Contraception prohibits the use of the menstrual cycle as a training feedback mechanism as true periods do not occur. Hence the athlete may be unaware of any changes in their cycle and bony changes may occur silently until reaching injury stage.

Fertility for female athletes can also be a major issue and maintaining normal menstrual function plays a key role.

· Endocrine System

Research on female athletes has shown adverse effects on thyroid function including changes in appetite regulating hormones, decreases in insulin and insulin-like growth factor, increased growth hormone resistance and elevated cortisol. This is likely an attempt at energy conservation by the body and may present as a tired, hungry athlete with poor body composition.

Low testosterone levels have been associated with chronic high intensity exercise loads and endurance sports in both males and females. Testosterone has an important role in building bone, and low levels are linked with low bone mineral density in male athletes. This link with Low Energy Availability means supplementation of testosterone in athletes is prohibited unless a medically diagnosed condition is present. In males, morning erections are an indicator of reproductive endocrine axis function with adequate testosterone levels.

· Metabolic

Low Energy Availability is correlated with decreased Resting Metabolic Rate. This results in negative effects on Body Composition for the athlete and they may present as weight gain in an athlete despite insufficient caloric intake.

· Haematological

Low Energy Availability may be both induced by, and contribute to, Iron deficiency. Iron is essential for carrying oxygen throughout the body and creating new blood cells. Iron deficiency therefore has negative impacts on exercise capacity and performance as well as impacting bone health, thyroid function, fertility and psychological wellbeing. Athletes in higher risk sports, particularly females, should be regularly monitored and if iron deficiency exists ensure co-ordinated management between a Sports Dietitian and Medical staff to ensure all causative factors are addressed.

· Growth and Development

Decreased Growth Hormone and IGF-1 levels are seen post exercise affecting the normal body response to exercise and ability to repair and build muscle. This can result in growth retardation in younger athletes. The long term effects of this are still being studied.

· Cardiovascular

Early atherosclerosis (hardening of the arteries) is associated with low estrogen and amenorrhoea. Other cardiovascular risk factors, including endothelial dysfunction affecting the lining of the arteries and changes in lipid profiles, have been linked to amenorrhoea in athletes. This may result in a seemingly healthy female athlete presenting with increased blood pressure and cholesterol levels. Other studies have demonstrated lower heart rates, lower systolic blood pressure and increased postural hypotension in amenorrhoeic athletes.

In male athletes, long-term high-volume high-intensity exercise has been linked with higher rates of cardiovascular disease compared with less active male athletes (Aengevaeren and Eijsvogels 2020). Exact mechanisms of this are still being determined however it is reasonable to consider nutrition may also have a role here.

· Gastrointestinal

Athletes, particularly those in our “higher risk sports” are renowned for having grumpy guts. Incidence of constipation and faecal incontinence are higher in athletes with Low Energy Availability.

· Immunological

Increased likelihood of illness (including gastrointestinal and upper respiratory tract), bodily aches and head related symptoms are seen in athletes with Low Energy Availability.

· Psychological

Psychological issues may be either a cause or result of Low Energy Availability. Negative effects on many aspects of psychological wellbeing are possible including increased depression symptoms and decreased ability to manage stress.


What effect does this have on Performance?

It is common for many athletes in weight sensitive sports to discuss “making race weight” or dropping kilograms to assist with performance. Does this really help? If the athlete is to drop into a state of Low Energy Availability, it is clear from the health effects that it will not benefit performance. The below infographic summarizes the direct influence on performance.

Further studies have found:

- Competition ranking is negatively correlated with energy availability in elite rhythmic gymnasts

- No difference in aerobic capacity in endurance athletes with normal menstrual function versus amenorrhoeic athletes who had lower body weight and fat mass. The amenorrhoeic athletes also showed decreased neuromuscular performance (measured via knee muscle strength and endurance) and worse reaction times. This suggests attaining a greater power to mass ratio for running performance through severe and persistent energy restriction negatively affects performance and health.

- A study of East African runners supported these findings.

- A study of national level Australian rowers found that failing to increase energy intake during a 4 week training block with 21% increase in load resulted in worsening performance during 5km time trials.

- Young elite swimmers with menstrual dysfunction were found to have a 10% decline in swimming velocity over a 400m time trial after a 12 week training block compared to an 8% increase in those with normal function.

For circumstances where an athlete legitimately needs to lose weight, a very fine balancing act is required to ensure adequate fueling is occurring for both health and performance. This should be done under the supervision of a Sports Dietitian at a gradual rate with a long term view and not viewed as a “get fast quick” solution.

What should I do if I am experiencing Low Energy Availability or RED-S?

It is important to identify athletes at risk of or currently experiencing RED-S for both long term health and sporting performance. Initial point of contact may occur through a Physiotherapist in seeking injury treatment but multidisciplinary team management is required. This team may include a Sports Physician, Sports Dietitian and Sports Psychologist in conjunction with the Athlete, Coaches and Physiotherapist. Treatment essentially involves an increase in energy intake, a decrease in exercise or a combination of both. Medical management of the various RED-S sequelae may also be required.



RED-S can be a major contributor to bone stress injuries and also recurrent soft tissue injuries. Recurrent illness, fatigue, athletic underperformance and psychological issues may also be indicators of RED-S. Athletes should ensure adequate energy intake to meet the training demands of their sport and for some sports this will require specific nutrition plans to be in place. These should be regularly monitored and adjusted as training/sports demands change. Incidence of Low Energy Availability in female athletes may be almost 50% in some sports and incidence is not linked directly to BMI. There is also emerging evidence that 32% of adult elite male athletes are affected. All sporting team members – athletes, coaches and health professionals – should be proactive in the prevention of RED-S to ensure the development of healthy, happy and high performing athletes.

Recent Posts

See All


Commenting has been turned off.
bottom of page