What is RED-S in Athletes?

April 5, 2022

Relative Energy Deficiency in Sport, also known as RED-S, is the imbalance of energy consumed through food and energy being used, particularly in athletes. This can be the result of increased physical activity while energy intake from food remains the same or even decreases. 

This energy imbalance causes physiological changes including, but not limited to, decreased immunity, interference with metabolism, impaired bone health and menstrual cycle disruption.

It is not uncommon for highly active people or athletes to consume less energy (calories) from their diet than what they require for daily activities alongside maintaining their training load and sustaining regular bodily functions.

This condition was formerly known as the female athlete triad (1 2), but in 2014 was renamed by the International Olympic Committee (IOC) to recognise the complexity of the condition and its effect on male athletes (3).


What are the symptoms of RED-S in athletes?

This is a complex condition that can manifest as many different symptoms, but some of the most recognisable signs include (1):

  •         Decreased muscle strength and/or endurance capacity
  •         Decreased concentration and mental cognition
  •         Increased or recurring injury or illness
  •         Irritableness
  •         Depression
  •         Menstrual cycle dysfunction
  •         Fatigue

Many of these symptoms are the result of hormonal imbalance and impaired metabolic function, due to a lack of available energy for the body (1, 4).

Changes to sexual reproductive hormones can influence mood and behaviour, as well as reproductive function including the menstrual cycle (4).

Low energy availability can cause fatigue which contributes to poor concentration levels, judgement and decision-making (4).


RED-S in athletes, male gymnast


Groups at risk of RED-S

This condition can occur in a vast range of athletes and active individuals, however, the most at-risk groups include athletes competing in aesthetically-driven sports (5) such as bodybuilding, gymnastics, and dancing (6), and weight-sensitive sports including boxing and lightweight rowing.

Another group identified as high-risk are long-distance and marathon runners, and other endurance athletes.

Young athletes are another high-risk group – the combination of increased training load and rapid growth throughout puberty and adolescence can lead to insufficient energy availability (7).


How serious is RED-S?

The underlying cause is an imbalance of energy supply and energy being used by the body, not only to keep up with training demands but with the daily needs of the body to maintain its regular functions and processes.

In the short term, this energy deficiency can cause increased fatigue, decreased athletic performance, and loss of periods in female athletes.

As the body runs out of energy to keep up with physiological demands, it begins to give up the functions that are least vital.

For some people with RED-S, frequent and recurring injury can occur. This is caused by a lack of available energy preventing proper muscle recovery. It also prevents muscles and tendons from strengthening over time. As a result, athletic performance weakens as lean muscle begins to breakdown and is not repaired (8).

Female athletes with the condition often lose their period as it is a process that the body quickly shuts down to preserve energy when it is scarce (1).

The effects of RED-S on physical performance may be an athlete’s biggest concern, however, it is important to recognise that the long-term impacts of an energy imbalance can be serious.


Nutrient deficiencies

Nutrient deficiencies resulting from inadequate energy intake can include low iron and B12 levels. Both of these deficiencies contribute to feelings of fatigue and neurological symptoms such as poor attention span and decision-making.

Various B-vitamins, including B12, as well as vitamin D and calcium, have been associated with increased risk of osteoporosis – the loss of tissue in the bone, causing them to become brittle and fragile (9).

If the onset of the condition is during adolescent and/or young adult years when bone density is developed, bone adaptation (strengthening due to use over time) and bone mineral density development is impaired, increasing the risk of breakages and osteoporosis (2).

Consequences can also be psychological – nutrient deficiencies can further contribute to mood instability and behavioural changes in the form of depression and other mental health struggles. 

To learn more about the roles of vitamin D and calcium in the body and their dietary sources, visit our previous blog articles on vitamin D and calcium.


marathon runners, RED-S in athletes


Hypothalamic amenorrhea

Irregular menstrual cycles experienced by female athletes may seem a convenient side effect of the condition, however, as the body’s fat stores reach increasingly low levels due to lack of energy, hormone function is impaired.

This type of period loss is called hypothalamic amenorrhea, as it is directly related to the ability of the hypothalamus region of the brain instructing the release of reproductive hormones (12).

If the condition continues over time, declining levels of estrogen can seriously impact bone production and maintenance (13).

Estrogen also plays a role in maintaining healthy cholesterol and blood pressure levels. Estrogen deficiency associated with hypothalamic amenorrhea, and subsequently RED-S, can lead to an increased risk of cardiovascular disease (CVD) and high blood pressure if not managed early (12).

It is important to note that an imbalance of sexual reproductive hormones can impact fertility of both male and female athletes.

Male athletes may experience declines in testosterone levels, which lowers libido and impacts muscle recovery and response to training.


Stress fractures

Declining fat stores can cause effects other than just disturbing the menstrual cycle and impacting performance.

As mentioned, low estrogen levels can interfere with bone production and maintenance.

This extends to male athletes as well as female, and results in stress fractures that may become recurring and/or difficult to recover from (13 14).

Studies on male individuals with low energy availability are limited, so there is very little knowledge on how this occurs and the long-term impacts.


How do I know if I have RED-S?

The multifactorial and complex nature of RED-S means it is experienced differently by each person, therefore each treatment plan is tailored by health professionals to the individual.

If you are a highly active person or athlete and are experiencing symptoms related to this condition, it is best to seek professional advice to determine the underlying cause of your symptoms.

Diagnostic tools such as the RED-S Clinical Assessment Tool (CAT) may be used by health professionals to evaluate people who are suspected to have the condition (15).


female rower, RED-S in athetes


What can be done about RED-S in athletes?

Ideally, the onset of RED-S is prevented, with the key prevention tool being education.

It is important to acknowledge that the majority of research in this area has been focused on RED-S in female athletes, drawing from knowledge of the female athlete triad. However, male athletes are equally impacted. This means that most resources focus on female health and treatment, but some principles apply to both groups.

In the past 2 years, the Australian Institute of Sport (AIS) has produced a series of short online education modules focusing on female performance and health. Modules available on the AIS website for public access include nutrition for female athletes, bone health, low energy availability, and menstrual abnormalities (16).

The British Journal of Sports Medicine has an ongoing partnership with the British Association of Sports Medicine. Together, these organisations have created “Health for Performance”; an online resource for the public to learn more about a range of health conditions that may impact athletes, with a specific focus on RED-S in both male and female athletes (17).

If you have been diagnosed with RED-S, the primary treatment approach is through making changes to the diet (18).

At Plant Nutrition and Wellness, our team of dietitians is experienced in helping people recover their menstrual cycle and correct low energy availability. You can book a discovery call here



RED-S is a condition experienced by many active individuals, largely by athletes, both male and female.

It refers to having an imbalance in energy taken in through the diet and the total energy used for regular daily activities, bodily functions and training.

The condition can be difficult to diagnose due to its complexity, and can appear as a range of signs or symptoms.

The effects of the condition can become serious if left untreated. It is important to seek help from a health professional, including a doctor and a dietitian, if you are experiencing symptoms of this condition.



  1.     https://bjsm-bmj-com.ez.library.latrobe.edu.au/content/bjsports/51/21/1570.full.pdf
  2.     https://journals.humankinetics.com/view/journals/ijsnem/22/2/article-p131.xml
  3.     https://bjsm.bmj.com/content/bjsports/48/7/491.full.pdf
  4.     https://link-springer-com.ez.library.latrobe.edu.au/content/pdf/10.1007/s40279-021-01491-0.pdf
  5.   https://blogs.bmj.com/bjsm/2019/04/22/relative-energy-deficiency-in-sport-red-s-recognition-and-next-steps/
  6.     https://www.frontiersin.org/articles/10.3389/fnut.2018.00136/full?=&field=&id=426685&journalName=Frontiers_in_Nutrition
  7.     https://blogs.bmj.com/bjsm/2017/04/12/young-athletes-optimal-health-part-3-consequences-relative-energy-deficiency-sports/
  8.     https://pubmed.ncbi.nlm.nih.gov/32902400/
  9.     https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4446754/
  10. https://www.plantnutritionwellness.com/vegan-vitamin-d-vegetarian-plant-based/
  11. https://www.plantnutritionwellness.com/vegan-calcium-food-sources-requirements-absorption/
  12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374026/
  13. https://journals.humankinetics.com/view/journals/ijsnem/29/2/article-p152.xml
  14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8294781/
  15. https://bjsm.bmj.com/content/bjsports/49/7/421.full.pdf
  16. https://www.ais.gov.au/fphi/education
  17. http://health4performance.co.uk/
  18. https://bjsm.bmj.com/content/51/21/1570


This article was co-written by student dietitian Lilee Lunney and PNW Clinic dietitian Megan Boswell.

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