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Relative energy deficiency in sport (also known as REDs) occurs when a person does not consume enough energy (calories) to help meet the demands of their training, which then leads to low energy availability. The athlete's performance and health eventually decline.

Athletes who try to reach a low body weight by overtraining or not consuming enough calories are at risk for REDs.

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REDs can affect both male and female athletes who perform at a high level of activity. It is estimated to affect 23 to 80% of female athletes and 15 to 70% of male athletes in a variety of sports.

REDs is a broader term that has replaced the previously named "Female Athlete Triad," as research has shown that low energy availability is not limited to females.

The female athlete triad was defined as three interrelated illnesses that may develop when a girl or young woman goes to extremes in dieting or exercise:

• Disordered eating. Abnormal eating habits (i.e., crash diets, binge eating) or extreme exercise keep the body from getting enough nutrition.
• Menstrual dysfunction. Poor nutrition, low calorie intake, high-energy demands, physical and emotional stress, or low percentage of body fat can cause hormonal changes that lead to irregular menses. Sometimes, menstrual periods will stop altogether (amenorrhea).
• Low bone mineral density. Lack of periods disrupts the body's bone-building processes and weakens the skeleton, making bones more likely to break. In the most severe cases, young female athletes can develop osteoporosis as a result of disordered eating and menstrual dysfunction.

However, this term was updated to relative energy deficiency in sport (REDs) in 2014 by the International Olympic Committee (IOC), as it was recognized that energy deficiency and its health consequences can affect athletes of either sex. The female athlete triad was then grouped as a subset of REDs because REDs can affect females and males differently.

The primary cause of REDs is an energy imbalance. When you burn more calories than you consume, you cannot sustain the amount of energy needed for normal daily function and exercise. This can happen with or without an eating disorder.

• Sometimes, a person unintentionally (by accident) does not consume an adequate amount of calories needed for training. You may not realize how many calories you are burning and simply not eat enough to replenish them.
• Sometimes, athletes intentionally (on purpose) restrict calories, exercise too much, or do both. For instance, wrestlers may severely limit food intake,  skip meals altogether, or work out more than usual to "make weight."

Regular calorie restriction can result in disordered eating, which may cause the following behaviors:

• Binge eating, then purging (bulimia)
• Fasting or skipping meals
• Restricting foods eaten, such as cutting out certain food groups (like carbohydrates) or eating only small portions of food
• Using diet pills or laxatives

A prolonged energy deficit can lead to health issues in both females and males involving multiple organ systems. Symptoms can vary widely depending on the individual and may include:

• Anxiety
• Difficulty concentrating
• Decreased athletic performance
• Depression
• Delayed recovery from injury or illness
• Fatigue
• Gastrointestinal issues
• Low bone density
• Recurrent (repeated) injuries or illnesses
• Recurrent (repeated) stress fractures
• Sleep issues
• Weight loss

Unlike females, who may have clear symptoms of a problem developing (i.e., a change in their menstrual cycle), males typically do not have clear symptoms of REDs.

In males, REDs can lead to issues such as:

• Decreased sperm count
• Delayed puberty
• Low libido
• Low testosterone
• Poor bone health/stress fractures
• Stunted growth or development

Recognition of REDs is an important first step in diagnosis and treatment. However, it can be challenging to admit that you have REDs or to recognize that a loved one has it.

Medical History

The physician may provide a questionnaire asking about eating and exercise habits. The doctor will take a detailed history, including asking questions about:

• Diet and eating habits
• Family history of medical issues
• General health
• Menstrual history (in females)
• Mood
• Past injuries (including broken bones or stress fractures)
• Physical activity
• Sleep patterns

Physical Examination

The physical examination will include:

• A musculoskeletal examination of areas of pain.
• A comprehensive head to toe evaluation. Sometimes, questionnaires may not fully identify REDs, so the physician may look for physical signs of issues affecting the following body systems:
  • Bone health
  • Cardiovascular health
  • Endocrine health
  • Gastrointestinal health
  • Immunity
  • Menstrual and reproductive health
  • Metabolism
  • Psychological health

Laboratory Tests

The doctor will order blood tests to identify any underlying nutritional, metabolic, hormonal, and/or endocrine abnormalities. These are some of the blood tests the doctor may order:

• Complete blood count (which screens for anemia)
• Complete metabolic panel (which measures electrolytes, including calcium, along with kidney and liver function)
• Vitamin D level
• Thyroid stimulating hormone (TSH)
• Ferritin (iron stores)
• Hormones (such as estrogen, testosterone, progesterone, LH, and FSH; these can be decreased in athletes)

Bone Mineral Density Testing (DXA Scan)

Athletes should have their bone mineral density evaluated if they have:

• A history of menstrual irregularity (females)
• Disordered eating
• A history of repeated or high-risk stress fractures

The DXA (dual-energy X-ray absorptiometry) scan is commonly used to assess bone mineral density. Measurement of the spine and hip is used in adults, while measurement of the spine and whole body is preferred in adolescents.

Bone mineral density should be rechecked every 6 to 12 months if symptoms of REDs continue.

Treatment should be under the guidance of a team of healthcare providers, including a primary care physician or sports medicine physician, dietitian, athletic trainer, physical therapist, gynecologist and/or endocrinologist, and psychologist.

The main goal of treatment is to restore energy balance to help support the athlete's health and enable them to safely participate in sports.

Restoring energy balance with a well-balanced diet is a key component of REDs treatment. It is also a good way to prevent REDs. 

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It is also important to improve bone mineral density. This can be done by modifying diet and exercise to increase total energy input and thus reverse the energy deficit.

In female athletes, it is important to restore menstrual cycles. This should happen naturally once the athlete regains normal energy availability. If normal menstrual cycles do not resume, and if the athlete has estrogen deficiency or infertility, hormonal treatment may help. Restoring menses — along with gaining weight — can also help to improve bone mineral density.

One or more of the following may be required to reach the above goals:

• Athletes may need to increase daily energy availability by 30 to 45 kcal of fat-free mass per day in their diet.
• A period of rest and reduced training load can help the body to recover.
• Supplementation with adequate vitamin D and calcium helps to maintain optimal bone mineral density. Aim for 32 to 50 mcg (1,280 to 2,000 IU) of Vitamin D and 1,200 mg of calcium (on average) daily through diet and/or supplements.
• If the athlete is intentionally restricting their diet or over-exercising, getting input from a mental health professional and sports nutritionist is important to help normalize eating habits and change any negative thoughts about body image and food.

Nutritional requirements can differ with individuals and can be complex, so it is important to reverse the energy deficit using a multidisciplinary approach.

Once an athlete is cleared to return to activity or sports, an athletic trainer or physical therapist can help design a personalized exercise program, which includes:

• A balance of impact and resistance exercises
• Well-defined sport-specific goals

Treating REDs is a process that will take time and commitment — think of it as a marathon, not a sprint. If you are being treated for RED-S, is important to follow your healthcare team's advice and to have regular check-ups with your doctors and providers to monitor your progress and ensure your overall health.

• REDs is a serious condition that can cause long-lasting effects on an athlete's overall health and performance.
• Early identification and treatment are essential to prevent long-term health problems.
• Treatment should be focused on restoring energy balance and addressing any physiological and mental health concerns under the guidance of a team of healthcare professionals.