Unintentional weight gain

Unintentional weight gain is gain of ≥ 5% of body weight over 6–12 months without a deliberate lifestyle change. Distinguish from fluid gain (which is faster and edematous). The differential splits cleanly into: (1) energy balance — sleep restriction, sedentary shift, ageing basal metabolic rate, post-menopause; (2) endocrine — hypothyroidism, Cushing's syndrome, insulinoma, growth hormone deficiency, PCOS; (3) medications — antipsychotics (olanzapine, quetiapine), antidepressants (mirtazapine, paroxetine), beta-blockers, insulin, sulfonylureas, corticosteroids, antihistamines, valproate; (4) psychiatric — depression, binge eating disorder, night eating syndrome; (5) fluid-driven — heart failure, nephrotic syndrome, cirrhosis, hypothyroid myxedema (these overlap with category 2).

• Energy balance drift — by far the commonest; chronically negative sleep + reduced activity.
• Hypothyroidism — slow gain, cold intolerance, fatigue, constipation.
• PCOS — central weight gain in women with irregular periods + hirsutism.
• Cushing's syndrome — central obesity, moon face, supraclavicular fat, purple striae.
• Drug-induced — antipsychotics, mirtazapine, paroxetine, beta-blockers, insulin, sulfonylureas, oral steroids.
• Depression / binge-eating disorder — affective + eating-pattern change.
• Menopause — typically 2–5 kg over the perimenopausal transition.
• Insulinoma — rare; hypoglycaemia drives eating.
• Fluid (heart failure, nephrotic syndrome, cirrhosis) — gain is fast (weeks), associated with leg/ankle swelling.

First-line panel for unexplained gain ≥ 5% / year: TSH ± free T4 (always — hypothyroidism is the cheapest treatable cause), fasting glucose + HbA1c (insulin resistance / pre-diabetes contributes to gain), LFTs (NAFLD often coexists), lipid panel. Add 24-hour urinary cortisol or overnight 1 mg dexamethasone suppression test if Cushing's features (central obesity, striae, hypertension, hyperglycaemia). Add LH/FSH/testosterone if PCOS suspected. Echocardiogram + BNP if fluid distribution suggests heart failure. Mediora.AI surfaces the thyroid + glycemic pattern; the diagnostic decision is GP / endocrinology.