Short answer: if you train a lot and eat too little, your body saves energy by turning down other jobs, such as recovery, muscle building and your hormone cycle. Sports medicine calls this low energy availability. More effort will not fix it. Enough food will.
What is low energy availability?
Energy availability is the energy left for your body after training has taken its share. When too little is left for too long, the body cuts back on things it sees as optional.
The International Olympic Committee describes the result as Relative Energy Deficiency in Sport, or REDs. It can affect hormones, bone health, immunity, mood and performance, and it is seen in recreational athletes as well as professionals (Mountjoy et al., 2023).
How does it affect hormones?
In a controlled study, young women ate different amounts for five days while their training stayed the same. When energy availability dropped below about 30 kcal per kilo of lean body mass per day, the hormone signal that drives the menstrual cycle was disturbed (Loucks & Thuma, 2003). This happened within days, long before any visible change.
What are the signs?
- Your period becomes irregular or stops
- You are tired all the time, even after rest days
- Your lifts stall or go down
- You get ill or injured more often
- You sleep badly, feel cold or feel low
- You think about food a lot
One sign alone proves nothing. Several together are a reason to look at how much you eat.
What can I do?
- Stop cutting food while adding training. Doing both at once is the most common cause.
- Eat around your sessions. A meal with carbohydrates and protein before and after training.
- Keep three full meals. Skipped meals are hard to make up later in the day.
- Train three good sessions, not six tired ones. Recovery is where progress is made.
- See your doctor if your period stops. A missing period is a medical signal, not a sign of fitness.
Questions women ask me
Can I still lose fat? Yes, with a small deficit and enough protein, not with very low calories next to hard training.
Can this happen at a normal weight? Yes. Energy availability is about what you eat compared with what you burn, not about your weight.
How fast does it recover? Energy and training often improve within weeks of eating enough. A missing period can take longer and needs a doctor's guidance.
Sources
- Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine. 2023;57(17):1073–1097.
- Loucks AB, Thuma JR. Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women. Journal of Clinical Endocrinology & Metabolism. 2003;88(1):297–311.
This article is general fitness information, not medical advice or a diagnosis.