Obesity — The Complete Medical Guide

Chronic positive energy balance from ultra-processed foods, energy-dense diets, refined sugars, saturated fats and oversized portions. The modern obesogenic food environment is the biggest single driver at population level.

Reduced total daily energy expenditure from prolonged sitting, desk work, long commutes, and screen time. Loss of muscle mass (sarcopenia) further lowers basal metabolic rate and worsens the deficit.

Polygenic risk — FTO, MC4R, LEP, LEPR gene variants alter appetite and energy storage. Epigenetic programming in utero also shapes lifelong adiposity set-point. 40–70% of BMI variance is heritable.

Hypothyroidism, Cushing's syndrome, PCOS, insulinoma, and growth-hormone deficiency all promote weight gain through altered metabolism or cortisol-mediated central adiposity. Screen in every new patient.

Chronic stress (hypercortisolaemia), depression, anxiety, binge-eating disorder, and emotional eating dysregulate the HPA axis and reward pathways, driving cravings for high-calorie comfort foods.

Corticosteroids, atypical antipsychotics (olanzapine, clozapine), mirtazapine, insulin, sulfonylureas, beta-blockers, and anticonvulsants are common culprits. Always review the medication list.

Sleep deprivation (< 6 h/night) elevates ghrelin and suppresses leptin, increasing hunger and cravings. Shift-work and disrupted circadian rhythm further impair glucose tolerance and insulin sensitivity.

Dysbiosis — altered Firmicutes-to-Bacteroidetes ratio — increases energy harvest from food and promotes low-grade systemic inflammation contributing to insulin resistance.

Food deserts, urban design discouraging physical activity, socio-economic status, cultural norms around food, and marketing of obesogenic foods all shape risk at population level.