Obesity and hormones

Hormones are chemical messengers that help regulate many of the processes in our body. They are one of several factors involved in obesity.

How hormones influence body fat#

Leptin, insulin, the sex hormones and growth hormone all affect our appetite, our metabolism (the rate at which the body burns energy), and where fat is stored on the body. In people who are obese, the levels of these hormones often shift in ways that encourage abnormal metabolism and the build-up of body fat.

Hormones are released into the bloodstream by a network of glands called the endocrine system. This system works alongside the nervous system and the immune system to help the body respond to different events and stresses. An excess or shortage of certain hormones can contribute to obesity, and obesity itself can in turn alter hormone levels.

Leptin and appetite#

Leptin is produced by fat cells and released into the bloodstream. It reduces appetite by acting on specific centres of the brain to dampen the urge to eat, and it also appears to help control how the body manages its fat stores.

Because leptin comes from fat tissue, leptin levels tend to be higher in people who are obese than in people of normal weight. Despite these higher levels, the body often becomes less sensitive to leptin, so the signal to feel full during and after a meal does not get through as well. Ongoing research is exploring why these leptin messages fail to reach the brain effectively.

Insulin, glucose and body fat distribution#

Insulin is produced by the pancreas and is important for regulating carbohydrates and the metabolism of fat. It stimulates tissues such as muscle, the liver and fat to take up glucose (sugar) from the blood. This keeps energy available for everyday functioning and maintains normal blood glucose levels.

In a person who is obese, insulin signals can be lost, and tissues become less able to control glucose levels. This can lead to type 2 diabetes and metabolic syndrome.

Where fat is stored also matters. Fat around the abdomen carries a higher risk of disease, such as heart disease, stroke and some forms of arthritis, than fat stored around the bottom, hips and thighs.

Sex hormones and age#

Estrogens and androgens help determine how body fat is distributed.

• Estrogens are sex hormones made mainly by the ovaries in women before menopause, and they trigger ovulation during each menstrual cycle.
• Men and women after menopause produce far less estrogen from the testes or ovaries; most of their estrogen is made in body fat, in much smaller amounts.
• In younger men, androgens are produced at high levels in the testes, and these levels gradually fall with age.

These age-related changes in sex hormones are linked to changes in fat storage. Women of childbearing age tend to store fat in the lower body (“pear-shaped”), while older men and women after menopause tend to store more fat around the abdomen (“apple-shaped”). Women taking estrogen supplements after menopause tend not to accumulate as much abdominal fat, and animal studies suggest that a lack of estrogen leads to excessive weight gain.

Growth hormone and inflammation#

The pituitary gland in the brain produces growth hormone, which influences height and helps build bone and muscle. It also affects metabolism. Research has found that growth hormone levels are lower in people who are obese than in people of normal weight.

Obesity is also linked with low-grade, ongoing inflammation in fat tissue. Excessive fat storage stresses the fat cells, which then release pro-inflammatory factors, as do immune cells within the fat (adipose) tissue. Overall, obesity is associated with a higher risk of several diseases, including cardiovascular disease, stroke and several cancers, and with reduced longevity and quality of life. For example, the increased estrogen made in the fat of older women who are obese is linked to a higher risk of breast cancer.

Why lost weight is often regained#

People who are obese tend to have hormone levels that favour the storage of body fat. Over time, behaviours such as overeating and a lack of regular exercise appear to “reset” the systems that regulate appetite and fat distribution, making the body more likely to gain weight.

The body constantly works to maintain balance, so it resists short-term disruptions such as crash dieting. Blood leptin levels drop after a very low-energy diet, and lower leptin can increase appetite and slow metabolism, which may help explain why crash dieters usually regain the weight they lost.

It is possible that leptin therapy could one day help people maintain weight loss in the long term, but much more research is needed. In the meantime, there is good evidence that long-term changes, such as healthy eating and regular exercise, can re-train the body to shed excess fat and keep it off. Weight loss through a healthy diet and exercise, or through bariatric surgery, has been shown to improve insulin resistance, reduce inflammation and beneficially shift obesity-related hormones. It is also linked with a lower risk of heart disease, stroke, type 2 diabetes and some cancers.

Key points#

• Insulin, a hormone produced by the pancreas, is important for the regulation of carbohydrates and the metabolism of fat.
• Fat around the abdomen is a higher risk factor for disease than fat stored on the bottom, hips and thighs.
• The body is always trying to maintain balance, so it resists short-term disruptions such as crash dieting.

Where to get help#