Did you know bone health and metabolism may be impacted in just 5 days of not eating enough?

A 2021 review by Areta et al concluded that “low energy availability shows to be a powerful physiological stressor that produces a dramatic shift in the endocrine milieu and metabolic response within days” so the importance of fueling for what you are doing as an athlete cannot be stressed enough.

What is Low Energy Availability (LEA)?

Energy availability (EA) is defined as the difference in energy intake (EI) and exercise energy expenditure (EEE) relative to fat free mass (FFM) (Areta et al, 2021). EA of <30kcals/FFM/day is considered to be clinically relevant (aka low energy availability) as the point at which endocrine and metabolic changes occur, though individuals that may experience negative impacts at higher or lower energy availability levels (Areta et al, 2021).

Impacts of Low Energy Availability

While short term periods of low energy availability (a few days to a few weeks) may not show immediate impact on training adaptation and performance (Melin et al, 2023), under the hood, significant changes to markers of bone formation and metabolic health start to occur within a few days and additional impacts accumulate with longer periods of energy deficit (Keay, 2022). These impacts are summarized in the chart below:

Unfortunately, Dr. Keay indicated in her recent social media post that it can take time “to reverse the energy saving adaptive changes in hormone networks” especially after long periods of low energy availability. Her statement is supported by the novel REFUEL study which examined the impact of increasing energy intake for 12 months on restoring menstrual function and bone health in female athletes with menstrual dysfunction. The study found that additional ~330kcals/day (18% energy intake increase) improved menstrual function (De Souza et al, 2021) but after 12 months of ~350kcals/day, did not improve bone mineral density, highlighting that it may take longer and/or more aggressive energy intakes to improve the impacts to bone health (De Souza et al, 2022).

So with the potential for significant impacts to your health, this is not a recommended fueling strategy:

A comprehensive sports nutrition assessment is a critical investment in your health, energy levels and your ability to perform to your potential, today and in the future. Ready to get started? Set up a complimentary introduction call to learn more.


Areta, J. L., Taylor, H. L., & Koehler, K. (2021). Low energy availability: History, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males. European Journal of Applied Physiology, 121(1), 1–21. https://doi.org/10.1007/s00421-020-04516-0

Melin, A. K., Areta, J. L., Heikura, I. A., Stellingwerff, T., Torstveit, M. K., & Hackney, A. C. (2023). Direct and indirect impact of low energy availability on sports performance. Scandinavian Journal of Medicine & Science in Sports. https://doi.org/10.1111/sms.14327

Keay, N. (2022). Hormones, health and human potential: A guide to understanding your hormones to optimise your health and performance. Sequoia Books.

De Souza, M. J., Mallinson, R. J., Strock, N. C., Koltun, K. J., Olmsted, M. P., Ricker, E. A., Scheid, J. L., Allaway, H. C., Mallinson, D. J., Kuruppumullage Don, P., & Williams, N. I. (2021). Randomised controlled trial of the effects of increased energy intake on menstrual recovery in exercising women with menstrual disturbances: The ‘refuel’ study. Human Reproduction36(8), 2285–2297. https://doi.org/10.1093/humrep/deab149

De Souza, M. J., Ricker, E. A., Mallinson, R. J., Allaway, H. C., Koltun, K. J., Strock, N. C., Gibbs, J. C., Kuruppumullage Don, P., & Williams, N. I. (2022). Bone mineral density in response to increased energy intake in exercising women with oligomenorrhea/amenorrhea: The refuel randomized controlled trial. The American Journal of Clinical Nutrition115(6), 1457–1472. https://doi.org/10.1093/ajcn/nqac044