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Hormones are chemical messengers that regulate processes in our body. They are one factor in causing obesity. The hormones leptin and insulin, sex hormones and growth hormone influence our appetite, metabolism (the rate at which our body burns kilojoules for energy), and body fat distribution. People who are obese have levels of these hormones that encourage abnormal metabolism and the accumulation of body fat.The hormone leptin is produced by fat cells and is secreted into our bloodstream. Leptin reduces a person’s appetite by acting on specific centres of their brain to reduce their urge to eat. It also seems to control how the body manages its store of body fat. Because leptin is produced by fat, leptin levels tend to be higher in people who are obese than in people of normal weight. However, despite having higher levels of this appetite-reducing hormone, people who are obese aren’t as sensitive to the effects of leptin and, as a result, tend not to feel full during and after a meal.
Body fat distribution plays an important role in the development of obesity-related conditions such as heart disease, stroke and some forms of arthritis. Fat around our abdomen is a higher risk factor for disease than fat stored on our bottom, hips and thighs. It seems that oestrogens and androgens help to decide body fat distribution. Oestrogens are sex hormones made at highest amounts by the ovaries in pre-menopausal women. They are responsible for prompting ovulation every menstrual cycle. Men and postmenopausal women do not produce much oestrogen in their testes (testicles) or ovaries. Instead, most of their oestrogen is produced in their body fat, although at much lower amounts than what is produced in pre-menopausal ovaries. In younger men, androgens are produced at high levels in the testes. As a man gets older, these levels gradually decrease. The changes with age in the sex hormone levels of both men and women are associated with changes in body fat distribution. While women of childbearing age tend to store fat in their lower body (‘pear-shaped’), older men and postmenopausal women tend to increase storage of fat around their abdomen (‘apple-shaped’). Postmenopausal women who are taking oestrogen supplements don’t accumulate fat around their abdomen. Animal studies have also shown that a lack of oestrogen leads to excessive weight gain.
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