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Athletes, energy availability and the consequences of REDs!

This blog is not only for those individuals characterised as an 'athlete' but for those regular gym goers that hit the gym week in and week out smashing their training programmes!

The fitness industry is surrounded by the words “energy balance, deficit and surplus” when it comes to those wanting to lose weight, maintain weight or even those that what to gain weight! However, very few understand the importance of ensuring athletes have sufficient daily energy availability in order to maximise performance within their sessions without compromising their overall health and physiological functions!

What is energy availability?

Energy availability is the amount dietary energy remaining after exercise training for all other processes, i.e. dietary energy intake (food eaten) minus the energy burnt during exercise, divide by the fat free mass (FFM) of an individuals. This gives you energy availability in 'kcals/kg FFM/day'.

Figure 1: Visual representation of the differences between energy balance and energy availability. (Areta, 2021)

Therefore when an athlete under-fuels i.e doesn’t consume enough food to match the energy burnt throughout the day from exercise/ training sessions and non exercise activity thermogenesis (NEAT- walking, sitting, breathing, living…) it results in low energy availability (LEA) which can then lead to relative energy deficiency syndrome (REDs) - the word in the title, and female athlete triad (FAT).

REDs is something that is now used frequently in the fitness industry and athletic population as it has the potential to explain a wide range of symptoms that negatively affect the health and performance of active individuals. It is defined as 'the impairment of physiological functions such as, metabolic rate, menstrual health, immunity, protein synthesis and cardiovascular health' (Mountjoy, 2018). Energy availability is the core of this REDs model, which is an extended model of the female athlete triad (FAT) that now states that male as well as females might also be affected. FAT was first of the two models, due to experts desperately trying to find a solution to a large number of female athletes showcasing the 'triad' symptoms; menstrual disruptions, osteoporosis (weakened bone health) and eating disordered (reduced energy availability). due to a lot of females under-eating for aesthetics around their sports and social media.

It is thought that individuals that have an energy availability of roughly ~45kcal/kg/FFN/d, is equivalent to an energy balance of 0 (what you need to maintain your current weight). Low energy availability however, is defined as any intake below the threshold of ~30kcal/kg/FFM/d.

Figure 2: Image from Mountjoy (2018), Physiological functions that are disrupted when athletes are in a LEA state.

Maintaining optimal energy availability to an athlete is crucial if they want to come close if not succeed in achieving the goals set (in a given sport or just during a specific training programme) or podium finish! Those that experience LEA are likely to negatively impact their performance through increased fatigue, risk of injury (stress fractures, muscle tears and sprains) as well as missed menstrual periods.

Other symptoms of REDs include

- Weight-loss/underweight

- Reduction in muscle size and strength

- Impaired recovery- increasing risk of overtraining and chronic fatigue

- Periods stopping/becoming irregular

- Weakened immune systems- illnesses such as colds and flus occurring frequently

- Mood chances

- Delayed/disordered growth in children and teen-ages

- Iron deficiency

It is worth commenting like everything in the sports industry, the way an individual experiences REDs will be different for each person therefore an individualised treatment programme is needed based upon the symptoms obtained, the sport, goals and personal circumstances of the athlete.


1. LEA may result from altered dietary behaviours that are caused by body dissatisfaction, the belief that lower body weight will result in greater performance, or the social pressure to look a certain way or through coaches, teammates and social media. Individuals and/or coaches should be cautious and aware of the common symptoms associated with REDs and try tackle them early doors to prevent absence from sports, gym or training.

2. Athletes should not worry about getting 'fatter' or 'slower' when energy availability is increased. Due to the demand of their exercise and the quality of nutrition consumed, it is likely that energy consumed meets the demands of the sport and results in energy balance

3. There is no single best diet. Individuals need difference energy needs depending on sport, lifestyle and dietary requirements. However, they should ensure adequate amounts of calcium, vitamin D and protein to support exercise and recovery

4. Individuals in an LEA (or even an energy deficit) should look at consuming a larger quantity of protein per day in order to preserve lean muscle mass. Aim for 2-2.5g per kg body weight per day

5. If you suffer from LEA, working with an qualified nutritionist that is knowledgable in the area of sports you participate in will allow you to increase your energy availability through energy intake, which will increase your resting metabolism and therefore prevents weight gain.


1. Mountjoy M, Sundgot-Borgen JK, Burke LM, et al

IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update

British Journal of Sports Medicine 2018;52:687-697.

2. Areta JL, Taylor HL, Koehler K. Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males. Eur J Appl Physiol. 2021;121:1–21.

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