New chapter: June 2019 - Please read disclaimer before proceeding
The body energy balance equation
A healthy level of physical activity is beneficial for all people; irrespective of age. It is also an integral part component of the body's energy balance equation. While this equation is different for everyone, it van be fundamentally summariesed as follows.
Energy intake (food) = Energy used for exercise (usually about 30%) + energy used for maintaining body functions (usually about 70%) + change in energy storage (mostly as fat).
(On a daily basis, the change in energy storage will be positive if more energy is consumed than is needed (i.e. weight will be increased) and negative if energy intake is inadequate (fat will be used up). Over the longer term we reach a weight balance for our usual food intake, exercise level. However it is not uncommon for female athletes to have a chronic negative daily balance and they often have insufficient fat stores to conpensate.
Athletes use more enegry than the average person
Athletes use much more energy during exercise than the average person and it is not uncommon for them to exercise excessively relative to their food intake. This is mainly a prpblem for young women athletes.
Relative energy deficiency in sport (RED-S) occurs in women who exercise excessively relative to the energy they consume from their food to the extent that the energy that they have left after that used for exercise is insufficient to maintain normal body functions, such as tissue repair, cell maintenance and replacement, maintaining the immune system, sexual functioning and, in young people, growth.
Consequences of Relative energy deficiency in sport
The bodies of women who have this insufficient 'Energy Availability' after exercise have to find ways to reduce energy use until a balance between intake and total use is achieved. If the problem is a temporary one, the deficit is usually small enough for the body to be able to do this without obvious symptoms occurring. If the situation continues, symptoms will eventually appear but even these can be subtle and easily missed in the early stages.
The body mediates this reduction energy use through the hypothalamus part of the brain which acts by altering levels of metabolic hormones and reproductive hormones. These hormonal changes result in changes to body composition and slowing, reducing or completely turning off some body functions. In women this can result in the following happening:
- Weight loss: The body can use fat stores to provide energy. When there are excess fat stores, then a premanent reduction in fat stores (and weight) is beneficial; and a lighter body uses less energy as well. However, when fat stores reach a critical level, the body will start to adopt other less healthy compensatory mechanisms. Using BMI (Body Mass Index) to assess weight in women athletes who have a lean body mass can be missleading as their extra muscle can mean that the woman can have a low normal BMI but still be energy deficient.
- Reduced metabolic rate leading to slower body functioning generally and to a reduction in the rate of body cell mainenance, body cell replacement, and body cell repair. These changes lead to:
- tiredness and fatigue (initially with exercise and more generally if the problem persists);
- decreased concentration;
- mpaired judgement;
- decreased co-ordination;
- decreased muscle strength;
- decreased endurance performance
- lower glycogen (a carbohydrate energy storage compound) storage levels
- reduced athletic performance, especially endurance performance
- poorer acaedemic performance
- increased risk of injury
- slower recovery from injury or from a major event (e.g. a half marathon)
- slower / poorer response to increased training schedule
- mood disorders including irritability and depression.
- Reduced immunity: This results in more frequent infections occurring.
- Other effects: Constipation
The symptoms / problems mentioned above are fairly non-specific and their often gradual onset means their cause is often hard to pick. They are just thought to be 'teenagers'. Many young women athletes are thought to be in this sub-clinical group. As the condition progresses, more specific symptoms develop.
- Reduced menstruation. The body can reduce energy expendature by inactivating the menstrual cycle. In women who have commenced their periods, this leads to fewer periods / irregual bleeding, or the complete cessation of periods. In girls who have not yet commenced menstruating, delayed onset of menstruation can occur. (This syndrome is termed functional hypothalamic amenorrhoea.) Many women are advised to go on the oral contraceptive pill to restore periods to 'normal' but this just hides the symptoms and does not help reduce effects such as stress fractures. A large number of female athletes are not aware that alterations in their periods are part of a broader problem that has significant current and long term problems. Particularly they are not aware of the association with bone health.
- Reduced fertility: Women with this syndrome also have problems with infertility and while this problem is considered to be reversible, restoring normal menstrual cycles / achieving pregnancy following signicant episode of amenorrhoea (no periods) can take many months / years; even after normal energy balance and normal weight are attained.
- Reduced bone density, stress fractures: The body reduces the density of its bones (i.e. they have a low bone meneral density). This can lead to recurrent stress fractures, obviously a huge problem for athletres. Even if the woman with the problem has a normal bone mineral density, stress fractures can occur due to the condition causing poor bone architecture (structure). The weight-bearing nature of some sports does not seem to protect against this loss of bone mineral density. By the time a woman presents with a stress fracture, the energy deficiency may have been present for many months or even several years.
- Osteoporosis in later life: If the condition persists for a long time, the resultant continuing low bone mineral density results in the woman attaining a lower peak bone mass (in her early twenties) than normal. (Peak bone mass occurs in the early twenties.) This lower peak bone mass is irreversible and is a major problem as a low peak bone density is a very important cause of osteioporosis in later life.
- Eating disorders: These can result from a fixation with weight / energy balance.
The problem can occur in younger girls also, especially dancers and gymnasts, with symptoms including delayed sexual development, delayed onset of periods and delayed growth.
For these reasons it is important that athletes, parents, coaches, schools, universities and sporting organisations are aware of:
- those women who are at increased risk
- the symptoms and signs of the condition
Who is at risk of 'relative energy deficiency in sport'?
The problem is more prevelent in activities where a thin body shape in seen as beneficial, such as dancing and gymnastics, or where a lower weight is can be advantageous, such as in long distance running.
The sports where women are at high risk of RED-S are:
- Endurance sports: Triathelon, running, cycling
- Aesthetic sports: Ballet, gymnastics and dance
- Weigh-classified sports where exercise is used to reduce weight (to reach a different classification: Rowing and martial arts
- Women who participate in multiple sports.
Reduced frequency of menstrual periods or complete abscence of periods occurs in about 12% of cyclists, and swimmers, 25% of distance runners and 60% of dancers. Distance runners who are not having periods have an incidence rate of stress fractures of 50% compared to about 30% in women runners who have regular periods.
The energy deficiency can be either unintended or intended.
Unintended energy deficiency: Insufficient energy intake is often uninitended as these athletes may still eat a lot of food. It's just that they exercise a lot too. The energy deficit is often not great and thus the problems often evolves gradually. This means that the changes the body can make to allow for the energy deficit allow weight and activity levels to remain unaffected for many months. When they do start to occur they come on gradually and thus are hard to pick up in the early stages. However, eventually tiredness, reduced performance, stress fractures and gradual weight loss start to occur.
Intended energy deficiency: Some sports / activities reward a low weight / slim figure and women participating in these activites are more likelly redude energy intake on purpose. It is important to identify women in this group so that they can receive early treatment and avoid the problems associated with longstanding eating disorders. (The new eating disorder classifications classify these women as being annorexic; although few women athletes suffer from significant annorexia nervosa or bulimia.) Behavious that indicate that energy restriction is being done intentionally include:
- adding extra training to the advised schedule
- skipping meals if a training session is missed or reducing intake while injured
- adding extra training after eating more than normal (e.g. eating out)
- guilt associated with rest days
- refusal to follow advice to increase energy (food) intake or reduce exercise schedule
- increasing restrictions on types of food eaten
Other dietary deficiencies: An important difference between the unintended and intended groups is that those who intentionally restrict food are more likely to have unbalanced diets and suffer from specific nutrient deficiencies as well as energy deficiency.
- Iron: Iron deficiency that can lead to anaemia is a good example and blood loss associated with the onset of menstruation exacerbates any iron deficiency problem. It is a problem for many young women. See section on iron deficiency.
- Calcium: Ensuring adequate calcium is present in the diet is obviously important. See section on calcium deficiency.
There are questionnaires available to help identiufy women at risk of RED-S. They are the Eating Disorder Inventory and LEAF-Q.
Treatment of 'relative energy deficiency in sport'
Early treatment helps avoid problems long term bone health and reduces the risk of long-term eating disorders occurring.
The mainstay is correcting the energy imbalance by:
- eating more. The help of a sports dietition may be beneficial.
- exercising less
- substituting current vigorous activities with less vigorous ones. Skills-based sports that require considerable practice time such as golf are a good choice.
These measures need to be suported by coaxches and in the case of children / adolescents, parents and success is shown by weight gain.
The presence of pathological eating attitudes or refusal to adopt the above advice needs to be viewed as an indication that an eating disorder has developed and referral to a psychologist / psychiatrist specialising in this area will probably be required.