The causes and treatment of obesity

The cause of obesity is an intake of metabolic fuels greater than is required for energy expenditure, so that excess is stored, largely as fat in adipose tissue reserves. The simple answer to the problem of obesity is therefore to reverse the balance reduce food intake and increase physical activity and hence energy expenditure. 

Lean people can increase their energy expenditure to match their food intake leptin (section 1.3.2) increases the activity of mitochondrial uncoupling proteins (section 5.1.3.1). The result of this is an increased rate of metabolism of metabolic fuels and increased heat output from the body, especially after meals and while asleep. 

Most people manage to balance their food intake with energy expenditure remarkably precisely. Indeed, even people who are overweight or obese are in energy balance and 

Very rarely, people are overweight or obese as a result of a physical defect of the appetite control centres in the brain — for example, some tumours can cause damage to the satiety centre, so that the patient feels hunger, but not the sensation of satiety, and has no physiological cue to stop eating. 

More commonly, obesity can be attributed to a psychological failure of appetite control. At its simplest, this can be blamed on the variety of attractive foods available. People can easily be tempted to eat more than they need, and it may take quite an effort of will-power to refuse a choice morsel. Even when hunger has been satisfied, the appearance of a different dish can stimulate the appetite. Experimental animals, which normally do not become obese, can be persuaded to overeat and become obese by providing them with a cafeteria array of attractive foods. 

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