Relative Energy Deficiency in Sports (RED-S)

Relative Energy Deficiency in Sports was first discussed in 2014, simply put is ‘impaired physiologically functioning due to relative energy deficiency’ (Mountjoy et al., 2014). This means the body has low energy availability usually due to intentional or unintentional underfueling (undereating). The consequences of underfueling stretch far and wide, impacting not only athletic performance and recovery but physiological functioning of important organs and bodily systems. The term RED-S was developed upon the previously discussed and well-known female athlete triad, a condition of many female athletes; the triad was composed of – menstrual irregularities, bone density issues (stress fractures) and disordered eating resulting in low energy availability. RED-S was created to be more inclusive of male athletes and to highlight all aspects of the signs and symptoms caused by low energy availability.

When discussing RED-S I want to emphasise the importance that this can happen to ANYONE of any athletic ability and level. This is not a syndrome exclusive to the elite professional athlete. Relative Energy Deficiency in Sport due to low energy availability can affect anyone who exercises or trains and does not nourish their body with enough food to support their output and allow adequate rest.

RED-S can impact our metabolic and endocrine functioning, digestive system, bone health, menstrual function, mental wellbeing, heart health, blood chemistry and production of red blood cells and cellular oxygenation processes, growth and development, muscle growth, repair and our immune system. Amongst this RED-S and underfueling severely impairs performance and recovery.

Low energy availability (LEA) is a disparity between energy intake (food) and the energy expended during exercise, which then leaves inadequate energy available to support the body’s physiological functions to maintain health and performance. Exercise Energy Expenditure (EEE) is additional energy expended above the energy required for daily living.

Various studies have shown that women require an average energy availability of 45kcal (188kJ) per kg of fat free mass (FFM) per day. Many of our organ systems and physiological systems are disrupted when energy availability drops to <30kcal/kg FFM/day. What does that mean? Well if someone who weighs 65kg and has a fat free mass of 52kg they would require 2,340 calories just to support daily functioning. It's important to note that daily intake of 30kcal/kg/FFM typically reduces our resting metabolic rate (RMR) in order to conserve as much energy as possible. RMR is the energy required for your body to simply function when completely at rest, not energy required to sustain exercise and furthermore to enhance performance and physiological functioning (Loucks & Thuma, 2003).

I’m sure many of you have been told to lose weight (as a female) you should be eating 1200calories per day and exercising as much as possible…. Well based on the scientific data and numbers mentioned above this would be putting you into starvation mode. I purposely don’t like to talk about weight as I feel this can be very polarising but also can cause many to become hyper focused and place their worth on said number. Also, we are all individual and one person may experience symptoms of RED-S or menstrual irregularity at a different energy deficit or body weight than another. No set body weight exists for every woman to achieve optimal health and menstrual function, it is unique and many other factors such as stress, sleep, time restricted feeding and genetics all contribute.

You can take all the supplements in the world but unless you eat enough for your output and allow adequate rest for optimal homeostasis you will be fighting an uphill battle. Many of the changes in hormonal function and organ systems occur in order to conserve energy and ensure the body has enough energy for absolutely vital processes to occur, such as pumping the heart to oxygenate the body, provide energy to the brain, and cause your lungs to function.

The health and physiological implications of low energy availability leading to RED-S effect the entire body. People may experience only a few symptoms or disruption to physiology, yet others may experience the entire spectrum of possible consequences of low energy availability. RED-S can have significant impact on the following:


Low energy availability decreases the bodies RMR. A severe energy deficit increases the hormone ghrelin – which is our hunger hormone whilst decreasing leptin, the hormone that cues satiety after eating, and insulin-like growth factor -1 which is responsible for growth and has an anabolic role in adults, thus promotes muscle growth and repair when in adequate amounts (Melin et al., 2015). This means our appetite regulation alters, hunger signals continue to be produced and our body cannot regulate and recover from exercise.

Endocrine system

LEA disrupts the hypothalamic-pituitary-gonadal axis, is a primary contributor to hypothalamic amenorrhoea, disrupts the thyroid gland (responsible for our body’s metabolism, temperature control, controls hormone levels and much more), alters our appetite control hormones (ghrelin and leptin), decreases insulin and insulin like growth factor, causes growth hormone resistance and elevates cortisol our infamous stress hormone. Men have been found to have reduced testosterone production, particularly in endurance athletes (Allaway, Southmayd, & De Souza, 2016; Berga et al., 2003)


Low energy availability may be partially induced by and also contribute to potential iron deficiency. Iron deficiency is commonly seen in athletes, particularly female athletes can directly contribute to energy deficiency. Iron deficiency anaemia has also been connected to altered bone health, hypothyroidism, infertility and mental well-being. Athletes have a higher demand for iron due to its role in haematopoiesis and oxygen transportation throughout the body as well as the phenomenon known as exercise induced haemolysis. Meaning the impact from running and other forms of exercise causes destruction of red blood cells and then higher need of iron for red blood cell production. This is primarily seen in runners but is associated with most sports (Petkus, Murray-Kolb, & De Souza, 2017; Telford et al., 2003; Tsigos & Chrousos, 2002).


People experiencing RED-S report a multitude of symptoms, LEA and excess exercise can cause constipation, symptoms of food intolerance, bloating, increased intestinal transit time, delayed gastric emptying, stool leakage, leaky gut syndrome and poor nutrient absorption (Clark & Mach, 2016; Norris et al., 2016). Digestive symptoms are a common complaint amongst the athletic population, many eliminate food groups, mainly gluten and dairy or go low FODMAP in a quest to resolve their digestive issues and discomfort. This is also a common reasons clients present to practice initially.

Menstrual Function

Impact on the menstrual cycle is well known but poorly corresponded and often overlooked. Low energy availability impacts the hypothalamus and it’s signalling to the pituitary gland and ovaries (HPO axis). This causes an overall decrease in LH, FSH, oestrogen and progesterone resulting in hypothalamic amenorrhoea. As mentioned, there is not set weight, specific length of time of low energy availability and high exercise that will trigger HA. It is unique. For some really great resources on all thing’s hypothalamic amenorrhea head over to Dr Nicola Rinaldi’s website No Period, Now What?

Bone Health

It has been long known that LEA, particularly in females, results in decreased bone health and bone remodelling. Low energy and HA are risk factors for increased stress injury such as fractures, many who experience RED-S and HA have decreased bone density and lowered bone remodelling markers, higher osteoclast to osteoblast ratio. Research has shown certain sports are at increased risk for low bone density, both men and women – runners, swimmers, cyclists and dancers (Loucks & Thuma, 2003).

It is important to note that low body weight in the form of BMI, <17.5 or weight loss >10% in one month are signs and indicators of LEA. Low BMI correlates to increased risk of low bone density in both sexes and higher risk of bone stress fractures or stress response (Meczekalski, Katulski, Czyzyk, Podfigurna-Stopa, & MacIejewska-Jeske, 2014; Nattiv et al., 2007)


HA and low oestrogen levels is associated with atherosclerosis, impaired cholesterol levels, arrhythmia's, bradycardia and hypotension. The more severe the energy deficit, particularly accompanied with disordered eating the more detrimental the potential consequence to heart health (O’Donnell & De Souza, 2004).


People with RED-S and underfueling will experience decreased immune function and are more susceptible to illness ranging from respiratory infections to gastrointestinal illness. In an already depleted system, the body will not be able to ‘launch an attack’ on invading pathogens (Shimizu et al., 2012).


Underfueling and RED-S has been correlated with higher propensity toward depression, body image issues, lower mental wellbeing and a diminished stress response (Mountjoy et al., 2014). In general, there is correlation between the greater the energy deficit or presence of disordered eating the greater the psychological impact.

Consequences on performance:

Long term low energy availability resulting in RED-S will impact athletic performance by hindering recovery, reduced physical and psychological capacity and impaired muscle function. The most commonly identified performance impairments include

· Decreased endurance performance

· Increased injury risk

· Decreased training response

· Impaired judgement

· Decreased coordination

· Decreased concentration

· Irritability

· Depression

· Altered glycogen stores

· Decreased muscle strength

Performance will be impaired due to altered glycogen storage and poor protein synthesis resulting in muscle derangement (amongst other things) which will impede consistent high-quality training. The increased risk of injury and illness may also interfere with training capacity.

Stay tuned for the next post on how to recognise, prevent and/or treat RED-S.

B x

Photo - Quino Al


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Berga, S. L., Marcus, M. D., Loucks, T. L., Hlastala, S., Ringham, R., & Krohn, M. A. (2003). Recovery of ovarian activity in women with functional hypothalamic amenorrhea who were treated with cognitive behavior therapy. Fertility and Sterility, 80(4), 976–981.

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