Is it possible to eat “clean,” train hard, and still feel worse? Unfortunately, yes – and low energy availability is one of the most common culprits. Quite often, this happens unintentionally. You start making healthier choices, eating “cleaner,” cutting back on certain foods without finding a suitable alternative, or training more consistently, and before you realise it, you are simply not eating enough - whether it be calories, carbs, fat, or protein - for everything your body is being asked to do. Energy demand doesn't just come from exercise. While people often think of energy in terms of movement or workouts, every system in the body needs fuel to run well, from our brain and immune system to hormone production, recovery, digestion, and reproductive health. So when energy availability is too low, the body interprets it as scarcity. The issue isn't just nutrient quality, but whether total energy and macronutrient intake are enough to support training, recovery, and the systems that keep you feeling well. Here’s what you need to know.
How Recovery Systems Shut Down
When energy is in short supply, the body stops investing in anything it sees as non-essential to immediate survival, meaning repair, resilience, and long-term maintenance begin to slip. Immune function, sleep quality, mood regulation, and tissue repair all depend on a steady supply of energy, so when our intake falls short, these systems are often among the first to suffer. Research on low energy availability links it with more frequent illness, poor bone health, slower injury healing, and low mood. In everyday life, that may look like being constantly run down, sleeping poorly despite feeling exhausted, or struggling with the kind of recurring injuries and recovery issues that never seem to fully resolve. Far from being separate issues, these can be some of the clearest signs that energy intake is no longer matching physiological demand. (8,9,10)
Under-Fuelling is Perceived as Stress
We can handle a little mismatch in energy consumption vs requirements, but when it becomes prolonged, the body interprets this as stress and shifts into the stress response, which is designed to protect us. One of the main systems involved is the hypothalamic–pituitary–adrenal (HPA) axis, which increases cortisol production. Cortisol, one of our primary stress hormones, helps keep blood glucose available for ‘fight or flight’, partly by prompting the body to make more glucose and, in more prolonged lack of energy, by breaking down muscle tissue to release amino acids. While this is an adaptive survival mechanism, it can leave us feeling more fatigued, make recovery harder, and even encourage fat storage around the mid-section despite continued restriction. This is often why people in a state of low energy availability describe feeling tired but wired, anxious, or unable to bounce back from training - all signs that the body is under ongoing stress during energy deficiency. (1,2)
Under-Fuelling + Reproductive Hormones
When the body senses that energy is in short supply, reproductive function suppression is a way of protecting essential survival processes. In women, this pattern over time can disrupt the hormonal signals that support ovulation, which can lead to lower progesterone, irregular or missing periods, and potential fertility challenges, something that’s commonly seen in functional hypothalamic amenorrhea. In men, low energy intake has also been associated with reduced testosterone, which can contribute to low libido, fatigue, and poorer muscle maintenance. Rather than failure, this is the body’s way of adapting to a lack of available energy. (3,4,5)
How the Thyroid Adapts
When the body senses that energy is in short supply, it often responds by becoming more efficient and conserving fuel. One of the ways it does this is through changes in thyroid hormone activity, including lower conversion of T4 into the more active T3, and an increase in reverse T3, which is an inactive form. Over time, this can reduce resting metabolic rate, essentially slowing the body down to cope with less energy coming in. Research on calorie restriction consistently shows this pattern, even when weight loss has plateaued. It can leave people feeling cold, sluggish, constipated, mentally foggy, and frustrated that their body seems to resist further weight loss despite eating less. (6,7)
Eat for Your Hormones
The endocrine system is one of the first places the effects of low energy availability begin to show; if you are doing everything “right” yet feeling progressively worse, the most effective intervention is often more control, but enough fuel to let the body function properly. Here’s how to support your system.
- 3 Balanced Meals - eating regular, balanced meals stabilises blood sugar and cortisol, supporting reproductive, thyroid, and metabolic hormone balance. Front load your nutrients so that you breakfast and lunch are providing the most energy and nutrient density, fuelling your body when it needs it most.
- Intentional snacks – if you’re a heavy exerciser, planning nutrient dense snacks between your longest meal gap (usually lunch-dinner) can help ensure you’re continuing to fuel your system.
- Protein - provides amino acids for hormone synthesis, supports muscle maintenance, and helps regulate blood sugar and appetite hormones.Aim for 1.2g per kg of bodyweight per day, or if pregnant, 1.6g per kg.
- Fat – essential for steroid hormone production, cell membrane integrity, and anti-inflammatory signalling. Only 1 in 5 of us are meeting the recommendation for oily fish intake, making a high qualtiy omega 3 supplement like Essential Omegas a strong addition to your daily regime.
- Fibre - slows carbohydrate absorption, supports gut health, and helps regulate insulin, leptin, and oestrogen metabolism. Currently, 96% of adults aren’t getting enough, so focus on 8-10 servings of veg and fruit per day, alongside high fibre powerhouses like beans and lentils. If you need support hitting your target, or are sensitive to high fibre foods, try Essential Fibre+.
- Antioxidants – protects cells from oxidative stress and support steroid hormone and thyroid function. Hitting the fibre, fruit and vegetable guidelines above will give a great dietary foundation of anti-oxidants. If you’re looking for supplemental support, try Deep Detox, which has N-Acetyl Cysteine and Alpha lipoic acid, both powerful antioxidants.
EXPLORE THE COLLECTION
Disclaimer: The information presented in this article is for educational purposes only and is not intended to diagnose, prevent, or treat any medical or psychological conditions. The information is not intended as medical advice, nor should it replace the advice from a doctor or qualified healthcare professional. Please do not stop, adjust, or modify your dose of any prescribed medications without the direct supervision of your healthcare practitioner.
References:
- Vamvini MT, Aronis KN, Chamberland JP, Mantzoros CS. Energy deprivation alters in a leptin- and cortisol-independent manner circulating levels of activin A and follistatin but not myostatin in healthy males. J Clin Endocrinol Metab. 2011 Nov;96(11):3416-23. doi: 10.1210/jc.2011-1665. Epub 2011 Aug 24. PMID: 21865351; PMCID: PMC3205881.
- Jeppesen JS, Hellsten Y, Melin AK, Hansen M. Short-Term Severe Low Energy Availability in Athletes: Molecular Mechanisms, Endocrine Responses, and Performance Outcomes-A Narrative Review. Scand J Med Sci Sports. 2025 Jun;35(6):e70089. doi: 10.1111/sms.70089. PMID: 40539747; PMCID: PMC12180388.
- Catherine M. Gordon, Kathryn E. Ackerman, Sarah L. Berga, Jay R. Kaplan, George Mastorakos, Madhusmita Misra, M. Hassan Murad, Nanette F. Santoro, Michelle P. Warren, Functional Hypothalamic Amenorrhea: An Endocrine Society Clinical Practice Guideline, The Journal of Clinical Endocrinology & Metabolism, Volume 102, Issue 5, 1 May 2017, Pages 1413–1439, https://doi.org/10.1210/jc.2017-00131
- Dobranowska K, Plińska S, Dobosz A. Dietary and Lifestyle Management of Functional Hypothalamic Amenorrhea: A Comprehensive Review. Nutrients. 2024 Sep 3;16(17):2967. doi: 10.3390/nu16172967. PMID: 39275282; PMCID: PMC11397038.
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- Moreira-Andres MN, Black EG, Ramsden DB, Hoffenberg R. The effect of calorie restriction on serum thyroid hormone binding proteins and free hormone in obese patients. Clin Endocrinol (Oxf). 1980 Mar;12(3):249-55. doi: 10.1111/j.1365-2265.1980.tb02707.x. PMID: 6771066.
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- Wasserfurth P, Palmowski J, Hahn A, Krüger K. Reasons for and Consequences of Low Energy Availability in Female and Male Athletes: Social Environment, Adaptations, and Prevention. Sports Med Open. 2020 Sep 10;6(1):44. doi: 10.1186/s40798-020-00275-6. PMID: 32910256; PMCID: PMC7483688.
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