Energy deficiency: the bare bones of RED-S

All athletes are (or should be aware) of the intimate connection between dietary habits and physical performance. But it’s not just about using nutrition to optimally fuel exercise and muscle growth/recovery. Dietary manipulation for weight management purposes can help athletes shed excess pounds, which almost invariably improves performance. This is especially true for sports where the force of gravity has to be overcome (for example in running and all running sports, cycling etc) and where a superior power-to-weight ratio is a key metric of performance.

The weight management danger

In their quest to improve performance, many athletes manipulate their diets with the goal of shedding excess weight. These weight management diets can help when used in a limited and controlled manner – for example, by eliminating empty/junk calories, or with mild calorie restriction for short periods of time. Some athletes approach weight management from the opposite direction – not by controlling calorie intake or quality, but simply by upping their training volume to shed some excess weight. Regardless of which weight management approach is used however, some athletes can over focus on weight and weight management, which in the longer term leads to unhealthy attitudes towards food/calories, health issues and poorer performance – ie eating disorders.

There’s no universally accepted definition of what constitutes ‘disordered eating’ in athletes, not least because there are several types of disordered eating behaviour, each with its own characteristics. What can be said however is that an eating disorder (ED) is characterised by an abnormal attitude towards food, which causes an athlete to change their eating habits and behaviour. In most cases, athletes with disordered eating tend to focus excessively on their weight and shape, leading them to make unhealthy choices about food, with damaging results to their long-term health and performance.

How common are eating disorders?

Despite the awareness among athletes and coaches about the issue of eating disorders, and the increased body of research into this topic, it remains an ongoing problem in both male but particularly female athletes, and across a wide range of participation levels. For example, a Norwegian study looked at over 1600 male and female elite athletes and compared the incidence of an ED with that in the general population⁽¹⁾. It found that many more athletes (13.5%) than controls (4.6%) had subclinical or clinical EDs. The prevalence of EDs among male athletes was four times higher in sports involving work against gravity (where low weight is an advantage) than in ball games (22% vs. 5%).

Meanwhile, the rate of ED among male endurance athletes was 9%. The prevalence of EDs among female athletes competing in aesthetic sports (high visibility sports such as swimming, gymnastics etc) was as much as 42% - higher than that observed in endurance sports (24%), technical sports (17%), and ball game sports (16%). The authors summed up their findings thus: “The prevalence of EDs is higher in athletes than in controls, higher in female athletes than in male athletes, and more common among those competing in leanness-dependent and weight-dependent sports than in other sports.”

Other studies into the problem of eating disorders have produced similar findings – ie that athletes participating in sports where ‘leaness’ is advantage or in aesthetic sports such as gymnastics are particularly at risk, especially female athletes. Moreover, this issue is one that is found across a wide range of sports and in many different nationalities and cultures; for example, studies report a high prevalence of eating disorders in French judo athletes⁽³⁾., Brazilian swimmers⁽⁴⁾, US runners and high school athletes^(5,6) – the list goes on. 

Many of the earlier studies into eating disorders among athletes referred to the incidence of the ‘female triad’ in female athletes. The female athlete triad was defined as the interrelatedness of energy (calorie) availability, menstrual function, and bone mineral density (BMD)⁽⁷⁾. BMD is a measure of the mineral content in bones, typically assessed to gauge bone strength and density; low levels increase fracture risk. Compared to the general female population, studies found a higher prevalence of abnormal menstrual function in the female athletic population^(8-10), which is worrying because of its negative impact on bone mineral density⁽¹¹⁾. However, in 2014, the International Olympic Committee expanded this concept to RED-S (Relative Energy Deficiency Syndrome), with the recognition that this condition can impact on both males and females⁽¹²⁾. An updated 2023 IOC consensus further refined the definition, describing RED-S as ‘a syndrome causing impaired physiological functioning due to low energy availability, with consequences like compromised bone health, blood disorders, and elevated injury risk’⁽¹³⁾.

RED-S and athletes

Just to clarify, RED-S refers to a condition in which (for whatever reason) athletes consume insufficient energy from food relative to the high demands of their training and competition, leading to disruptions in physiological functions. This imbalance can affect multiple body systems, including the musculoskeletal system, which encompasses bones and muscles. As we’ve mentioned above, athletes can unwittingly stumble into RED-S, either as a result of an over-enthusiastic approach to weight management, or as a result of a longer-term eating disorder. Regardless, these athletes (of both sexes) may experience declining sport performance as a result, often along with health complications like increased injury risk and even fractures.

Although a there’s been a lot of research into RED-S and the female triad, the underlying metabolic processes causing the condition are not well understood, particularly when it comes to bone metabolism. Bone metabolism involves the balance between bone formation (building new bone by cells called osteoblasts) and bone resorption (breaking down of old bone by cells called osteoclasts). Some research has indicated that athletes with RED-S suffer from suppressed bone metabolism⁽¹⁴⁾; however, few studies have investigated the direct link between these changes directly to BMD within the same group of individuals. Also, much of the research to date has focused solely on female athletes (female triad studies), thereby overlooking male athletes who make up around one fifth of the total number of RED-S diagnoses⁽¹³⁾.