In a previous blog-post we defined what energy availability is and what typically is considered to be ‘low energy availability’ (LEA). Briefly, energy availability is the dietary energy available to sustain normal physiological function after subtracting exercise energy expenditure. LEA is important because it is the key etiological factor for health and performance impairments outlined in the ‘triad’ and the RED-S models.
To understand what these models predict in relation to the effects of LEA, we must first understand the body of evidence that supports them. On the one hand we have very well controlled short-term laboratory-based studies looking at the acute effect of LEA, and on the other hand we have ‘cross-sectional’ studies that examine the characteristics of populations that are thought to have been exposed to LEA for longer.
Short-term studies on LEA
The studies showing a cause-effect between LEA and endocrine and physiological dysregulations have been carried out in highly controlled settings and are of 3-5 days duration only. Of these, the majority were conducted in young healthy sedentary females and only one of these studies directly addressed the effect on endurance-type performance.
As a whole, these studies provide support to the idea that LEA affects early hormonal and metabolic markers associated to impairment of reproductive function (females) and bone metabolism, increase in hunger, down-regulation of resting metabolic rate and muscle protein synthesis, among other factors.
The one study that looked at the effect of LEA on aerobic-type performance, however, did not show a negative effect. In line with this, we must highlight that changes in early markers of endocrine and physiological function may take longer than 3-5 days to result in physiological disruptions that are big enough to result in impaired health and physical capacity. Based on short studies we cannot predict the magnitude and duration of LEA to result in substantial physiological disruption.
Cross-sectional studies on LEA
While the literature on which the triad and RED-S models are based also contemplates short-term studies on LEA, it is predominantly based on cross-sectional studies. These type of studies examine the characteristic of populations which are thought to have been exposed to LEA compared to a similar population without being exposed to LEA (e.g. amenorrheic vs eumenorrheic athletes). Based on current evidence, these models predict that LEA result in a plethora of complications such as reduced bone density, impaired reproductive and immune function and cardiovascular, metabolic and gastrointestinal complications, and impair performance, just to name a few.
In reality the time of exposure to LEA in the populations from cross-sectional studies is unknown. It is also unknown what other factors, in addition to LEA, may be contributing to the health and performance impairments of the different groups.
Based on current evidence, low energy availability results in a plethora of complications such as reduced bone density, impaired reproductive and immune function, and impaired performance.
This is not to say that these type of studies are bad or useless: they are an essential part of scientific knowledge. They may lack control, but they have high ecological validity. However, this leaves us with a gap in our understanding what the effect of moderate exposure to LEA may be.
Moderate exposure to LEA and physical capacity
Case studies from our group bridge some of the current gaps in this knowledge and suggest that short-term exposure to LEA may result in desired outcomes in some training-nutrition interventions.
We recently reported a tightly controlled weight-making intervention of a male combat-sport athlete in preparation for competition. Over 8 weeks of heavy training the athlete was exposed to 18 kcal/kg FFM/day on average, losing ~10 kg of body mass (~5kg fat mass) in this period to reach his weight category. Throughout this period both relative and absolute maximal aerobic capacity increased, as well as his relative and absolute lower and upper body strength. In another case-study, we also show how a male masters triathlete improved his maximal aerobic power after recovery from surgery in preparation for a long-distance triathlon while being exposed to an energy availability of 29 kcal/kg FFM/day for 18 weeks, resulting in loss of ~5 kgs of body (~2.5 kg fat mass).
Short-term exposure to low energy availability may result in desired outcomes in some training-nutrition interventions.
These preliminary data suggest that well-planned training-nutrition interventions may allow to cope with heavy training while also being in an energy availability that results in weight loss. It is important to highlight, however, that we do not advocate for chronic or extreme weight-loss practices and we are well aware that undesired underfuelling can be an issue in many sports. The focus should be placed in providing the right type and amount of macronutrients at the right times. But, in line with the contemporary sports demands, sometimes some exposure to LEA is necessary and may result in positive performance outcomes.
So in the end, will energy availability hamper performance?
While it seems very likely that —in fact— severe and/or prolonged LEA can have a negative effect on health and performance, the effect of shorter duration, controlled LEA is not well understood, and shorter periods of reduced energy availability may be desired at times in some sports.
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.
De Souza MJ, Nattiv A, Joy E, Misra M, Williams NI, Mallinson RJ, et al. 2014 Female Athlete Triad Coalition Consensus Statement on Treatment and Return to Play of the Female Athlete Triad: 1st International Conference held in San Francisco, California, May 2012 and 2nd International Conference held in Indianapolis, Indiana, May 2013. British Journal of Sports Medicine. 2014;48:289–289.
Langan-Evans C, Germaine M, Artukovic M, Oxborough DL, Areta JL, Close GL, et al. The Psychological and Physiological Consequences of Low Energy Availability in a Male Combat Sport Athlete. Medicine & Science in Sports & Exercise. 2021;53:673–83.
Louis J, Tiollier E, Lamb A, Bontemps B, Areta J, Bernard T. Retraining and Nutritional Strategy of an Endurance Master Athlete Following Hip Arthroplasty: A Case Study. Front Sports Act Living. 2020;2:9.
Mountjoy M, Sundgot-Borgen J, Burke L, Ackerman KE, Blauwet C, Constantini N, et al. International Olympic Committee (IOC) Consensus Statement on Relative Energy Deficiency in Sport (RED-S): 2018 Update. International Journal of Sport Nutrition and Exercise Metabolism. 2018;28:316–31.