Irregular periods and weight loss: what to know

The reproductive system responds to available energy, nutrition, exercise, and physical stress. A large change in weight, restrictive eating, or heavy training can delay ovulation or stop it, leading to late, light, or absent periods. Unplanned weight loss may point to thyroid disease, digestive illness, infection, diabetes, medication effects, or another condition. Polycystic ovary syndrome, anovulation, perimenopause, and premature ovarian insufficiency can also affect cycles, so weight change alone does not identify the cause.

Record your bleeding pattern, weight trend, food intake, exercise, sleep, medicines, bowel symptoms, thirst, and fatigue. If pregnancy is possible, test. Avoid further restriction or intense exercise until you have personalised advice, and seek help from a clinician or dietitian if eating feels difficult or fearful. A medical review may include questions, examination, pregnancy testing, blood tests, and sometimes ultrasound. Treatment focuses on the reason for the weight loss and the cycle change rather than the scale alone.

Arrange prompt care for ongoing unplanned weight loss, missed periods, marked weakness, dizziness, fainting, vomiting, or signs of dehydration. Seek urgent help for severe abdominal pain, very heavy bleeding, or possible pregnancy with pain or bleeding.

Could low energy availability explain my cycle? What tests should check unplanned weight loss? How can I restore health while respecting my eating and activity needs?