--- title: "When training affects your periods: RED-S" description: "How not eating enough for your training can affect periods, bones and performance, and how to get support with food and rest." url: "https://myruva.co/learn/red-s-low-energy-availability-and-periods" language: "en-GB" topic: "Hormones" published: "2026-10-18" updated: "2026-10-19" author: "Ruva team" reading_minutes: 4 --- # When training affects your periods: RED-S How not eating enough for your training can affect periods, bones and performance, and how to get support with food and rest. *Written and reviewed by the Ruva team · Updated 2026-10-19 · Hormones* ## Key points - Low energy availability means you’re not eating enough to cover your exercise and your body’s other needs. - If your periods stop while training, get checked. Losing them is not a sign of fitness. - RED-S can weaken bones and raise the risk of fractures. - Support may include help with food, changes to training and psychological care. If you lose your period while training, ask for medical advice. Not eating enough for your exercise and your body’s other needs can affect your hormones and bones. Losing your period is not a training goal to aim for. ## What low energy availability means Relative Energy Deficiency in Sport is usually shortened to RED-S or REDs. It happens when your body doesn’t have enough energy, and it affects both health and performance. Your body needs energy for everyday functions as well as for exercise. You can fall short without meaning to eat less. You use energy outside training too. Walking, cycling to work and active jobs all use energy. Oxford University Hospitals notes that with a busy routine, you may need to plan to fit in enough food. Think about your whole day when you describe your activity to a clinician or dietitian. Appetite isn’t an exact guide to how much you need. Training can make you feel less hungry. If eating around exercise has become hard, mention it, even if you don’t feel hungry after a session. ## Why periods and bones matter together When you’re short of energy for a long time, the body saves energy by slowing some functions down. Reproductive hormones can be affected. Clinicians may consider functional hypothalamic amenorrhoea. This is one possible reason periods stop, when the part of the brain that controls them slows down. They need to rule out pregnancy and other causes first. Your bones can suffer too. RED-S is linked with lower bone density and a higher risk of fractures, including stress fractures. Tell the clinician about any past fractures or repeated injuries as well as changes to your periods. Checks for suspected hypothalamic amenorrhoea include asking about past fractures. A bone density scan may be considered if your periods have been missing for a long time. It may be done sooner if a lack of nutrients or fragile bones is suspected. This is the clinician’s decision. A period diary can’t measure how strong your bones are. ## Getting enough energy again Care aims to give you enough energy for daily life and training again. That can mean eating more, eating better and exercising less. Some people need to stop training for a while. The Endocrine Society notes that fixing the energy gap often means gaining weight. Agree a plan with a clinician and a dietitian that fits your needs. Psychological support can be part of care. If changing what you eat or how you exercise feels frightening, or you find it hard to let go of rules around them, say so. Eating disorders can affect people of any weight, including people who look healthy. Hormonal contraception makes things more complicated. The Endocrine Society warns that the pill can hide whether your natural periods have come back. It also warns that bone loss may carry on if the energy gap carries on. Don’t stop a prescribed medicine without talking to your doctor. Ask how your care team will check your recovery while meeting your contraception needs. Irregular or missing periods don’t mean you can skip contraception. If you could get pregnant and don’t want to, you still need it. Ovulation can be hard to predict. Ask your clinician about suitable contraception alongside your recovery plan. ## Symptoms that need urgent help Call 999 now (UK), 911 (US), or your local emergency number, if you have heart palpitations (a pounding or fluttering heartbeat) with chest pain, breathlessness, feeling faint or fainting. Call the same emergency number if someone faints during exercise or doesn’t fully recover. Contact an urgent GP service or NHS 111 today (UK), or get urgent medical care today (US and elsewhere), if dizziness when you stand up doesn’t settle or you’re passing less urine than usual. ## Bring the whole picture to an appointment Book a GP appointment in the UK, or see your doctor or a sports medicine clinician in the US and elsewhere, if your periods stop or become irregular. The NHS advises a check if you miss your period 3 times in a row. It advises going sooner if a missed period comes with symptoms such as tiredness or weight changes. You can raise worries before you reach that point. Bring notes about your training, meals, sleep, stress, period dates and injuries. The Endocrine Society advises clinicians to ask about all of these. Add the part you find hardest to explain, such as fear of resting. Ask who will join up your nutrition and medical follow-up. ## When to get help - **Emergency:** Call 999 now (UK), 911 (US), or your local emergency number, if you have heart palpitations (a pounding or fluttering heartbeat) with chest pain, breathlessness, feeling faint or fainting. Call the same emergency number if someone faints during exercise or doesn’t fully recover. - **Same day:** Contact an urgent GP service or NHS 111 today (UK), or get urgent medical care today (US and elsewhere), if dizziness when you stand up doesn’t settle or you’re passing less urine than usual. - **Book an appointment:** Book a GP appointment (UK), or see your doctor or a sports medicine clinician (US and elsewhere), if your periods stop or become irregular during training, especially with weight changes or tiredness. ## Where you live Services and advice differ between countries. - **UK:** NHS guidance advises seeing a GP if you miss your period 3 times in a row, or if your periods become irregular. - **US:** The Endocrine Society advises a check when periods have stopped for 3 months or more in people being assessed for functional hypothalamic amenorrhoea. - **Elsewhere:** Elsewhere, ask your doctor about changes to your periods and support with eating and training. ## Sources 1. [Relative Energy Deficiency in Sport (RED-S)](https://www.ouh.nhs.uk/media/0f2nd3pe/115727energy.pdf), Oxford University Hospitals NHS Foundation Trust 2. [Missed or late periods](https://www.nhs.uk/symptoms/missed-or-late-periods/), NHS 3. [Eating Disorders: What You Need to Know](https://www.nimh.nih.gov/health/publications/eating-disorders), National Institute of Mental Health 4. [Hypothalamic Amenorrhea Guideline Resources](https://www.endocrine.org/clinical-practice-guidelines/hypothalamic-amenorrhea), Endocrine Society 5. [Progesterone Test](https://medlineplus.gov/lab-tests/progesterone-test/), MedlinePlus 6. [Heart palpitations](https://www.nhs.uk/symptoms/heart-palpitations/), NHS 7. [Fainting](https://www.nhs.uk/symptoms/fainting/), NHS 8. [Dehydration](https://www.nhs.uk/conditions/dehydration/), NHS --- This guide is general information to help you keep and use your own records. It isn’t medical advice. If you’re worried about a symptom, or something changes suddenly, talk to a doctor, nurse or pharmacist.