1. Specific Factors: In few cases of obesity, the cause can be isolated and treated e.g
a) Endocrine disorders such as hypothyroidism, Cushing's syndrome, hypothalamic tumours or injury, insulinoma etc.
b) Drugs: Drug treatments with tricyclic antidepressants, sulphonylurea, some oral contraceptives, corticosteroids, sodium valporate, etc.
2. Behavioural Factor: The leading factor to obesity is decrease in activity levels. The following lifestyle predisposes an individual to obesity or overweight.
a) Intake of high-fat diet: Most consumed fats induce very little energy expenditure as they are mostly stored.
b) Eating of junks: Is a common lifestyle nowadays. Snacking and the loss of formalised meal pattern reduces the conscious recognition of foods eaten.
c) Consumption of energy-dense foods and drinks
d) Alcohol consumption: It stimulate appetite and promotes weight gain by providing substantial energy.
3. Genetic Factors: The following genes have been implicated:
a) Mutation of melanocortin-4 receptor (MC4R)
b) Prader-Willi syndrome( childhood obesity with abnormal appearance and CNS function)
c) Mutation in Leptin gene ( Leptin is thought to be a blood borne signal from the adipose tissue that informs the brain about the size of fat mass, as well as acting as signal to regulate appetite or energy.