When training affects your periods: RED-S

Losing your period while training is a reason to ask for medical advice. Too little food energy for the exercise you do and your body’s other needs can affect hormones and bone health. Missing bleeding is not a training milestone to aim for.

What low energy availability means

Relative Energy Deficiency in Sport, usually shortened to RED-S or REDs, describes a condition that affects health and performance when energy availability is too low. Your body needs energy for everyday functions as well as exercise. You can fall short of the energy you need without deliberately trying to eat less.

Energy needs extend beyond training. Walking, cycling to work and physically active jobs also use energy. Oxford University Hospitals notes that a busy routine can require planning to fit in enough food. Consider the whole day when you describe your activity to a clinician or dietitian.

Appetite is not a precise measure of those demands. Training sessions can suppress appetite. If eating around exercise has become difficult, mention it, even if you do not feel hungry after a session.

Why periods and bones matter together

When an energy shortage persists, the body can conserve energy by slowing some functions. Reproductive hormones can be affected. Clinicians may consider functional hypothalamic amenorrhoea, one possible explanation for absent periods, but they need to exclude pregnancy and other causes first.

Bone health can also suffer. RED-S is associated with lower bone density and a greater risk of fractures, including stress fractures. Tell the clinician about previous fractures or recurring injuries as well as period changes; assessment of suspected hypothalamic amenorrhoea includes a history of fractures.

A bone-density scan may be considered after prolonged absence of periods, or earlier if nutritional deficiency or bone fragility is suspected. This is a decision for the clinician. A period diary cannot assess bone strength.

Getting enough energy again

Care aims to restore enough energy for daily life and training. That can involve increasing food intake, improving nutrition and reducing exercise; some people need to pause training. The Endocrine Society notes that correcting the energy imbalance often requires weight gain. Agree a plan with a clinician and a dietitian that fits your needs.

Psychological support can be part of care. If changing food or exercise feels frightening, or rules around them are hard to step away from, say so. Eating disorders can affect people across body weights, including people who appear healthy.

Hormonal contraception complicates the picture. The Endocrine Society cautions that oral contraceptive pills can mask the return of spontaneous periods and that bone loss may continue if the energy deficit continues. Do not stop a prescribed medicine without talking to your doctor. Ask how your care team will assess recovery while meeting your contraceptive needs.

Irregular or absent periods do not remove the need for contraception if pregnancy is possible and you do not want to become pregnant. Ovulation can be unpredictable. Ask your clinician about suitable contraception alongside the recovery plan.

Symptoms that need urgent help

Call 999 now (UK), 911 (US), or your local emergency number, if you have heart palpitations with chest pain, breathlessness, feeling faint or fainting. Call the same emergency number if someone faints during exercise or does not fully recover.

Contact an urgent GP service or NHS 111 today (UK), or seek urgent medical care today (US and elsewhere), if dizziness on standing does not settle or you are passing less urine than usual.

Bring the whole picture to an appointment

Book a GP appointment in the UK, or see your doctor or sports-medicine clinician in the US and elsewhere, if periods stop or become irregular. The NHS advises review after missing your period 3 times in a row, and sooner when a missed period comes with symptoms such as tiredness or weight changes. You can raise concerns before reaching that point.

Bring notes about training, meals, sleep, stress, period dates and injuries. These are all areas the Endocrine Society advises clinicians to ask about. Add the part you find hardest to explain, such as fear about resting, and ask who will coordinate nutrition and medical follow-up.