What causes unexplained weight gain?

A change on the scales may reflect body fluid rather than body fat. Salt intake, menstrual or reproductive changes, some heart or kidney problems, and certain medicines can cause fluid retention. Reduced activity, increased appetite, stress, or disrupted routines can also gradually change weight without being obvious day to day.

Medical causes include an underactive thyroid, metabolic syndrome, obesity, and obstructive sleep apnoea. Poor sleep can affect appetite and energy, while thyroid hormone changes may bring tiredness, feeling cold, dry skin, constipation, or a slower heartbeat. One symptom alone cannot identify the cause.

Note when the change began, how quickly it occurred, medicines and supplements, appetite, sleep, bowel habits, menstrual changes, and swelling of the legs or abdomen. Weigh under similar conditions and avoid extreme dieting while the cause is being explored.

Arrange a clinical review if the gain continues or has no clear explanation. Assessment may include a medicine review, examination, blood tests for thyroid function and glucose, and consideration of sleep symptoms. A weight management programme, thyroid treatment, or another targeted plan depends on the finding.

Seek urgent help for sudden swelling with breathlessness, chest pain, fainting, or severe weakness. Contact a clinician promptly for rapid ongoing gain, marked swelling, reduced urination, severe tiredness, or weight change after starting a medicine. Loud snoring with pauses in breathing and daytime sleepiness also warrants assessment.

Ask: Could this be fluid retention or a medicine effect? Should my thyroid, glucose, or kidney function be checked? Do my sleep symptoms suggest obstructive sleep apnoea? Which weight support is suitable for me?