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.
A system of glands, known as the endocrine system, secretes hormones into our bloodstream. The endocrine system works with the nervous system and the immune system to help our body cope with different events and stresses. Excesses or deficits of hormones can lead to obesity and, on the other hand, obesity can lead to changes in hormones.
The pituitary gland in our brain produces growth hormone, which influences a person’s height and helps build bone and muscle. Growth hormone also affects metabolism (the rate at which we burn kilojoules for energy). Researchers have found that growth hormone levels in people who are obese are lower than in people of normal weight.
The hormone leptin is produced by fat cells and is secreted into our bloodstream. Leptin reduces a person’s appetite by acting on specific centers of our brain to reduce our 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.
Insulin, a hormone produced by the pancreas, is important for the regulation of carbohydrates and the metabolism of fat. Insulin stimulates glucose (sugar) uptake from the blood in tissues such as muscles, the liver, and fat. This is an important process to make sure that energy is available for everyday functioning and to maintain normal levels of circulating glucose.
In a person who is obese, insulin signals are sometimes lost and tissues are no longer able to control glucose levels. This can lead to the development of type II diabetes and metabolic syndrome.
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 estrogens and androgens help to decide body fat distribution. Estrogens are sex hormones made by the ovaries in women. They are responsible for prompting ovulation every menstrual cycle.
Men and postmenopausal women do not produce much estrogen in their testes (testicles) or ovaries. Instead, most of their estrogen 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 estrogen supplements don’t accumulate fat around their abdomen.
Inflammatory Factors and Excess Weight
Obesity is also associated with low-grade chronic inflammation within the fat tissue. Excessive fat storage leads to stress reactions within fat cells, which in turn leads to the release of pro-inflammatory factors from the fat cells themselves and immune cells within the adipose (fat) tissue.
Obesity hormones as a risk factor for disease
Obesity is associated with an increased risk of a number of diseases, including cardiovascular disease, stroke, and several types of cancer, and with decreased longevity (shorter life span) and lower quality of life. For example, the increased production of estrogens in the fat of older women who are obese is associated with an increase in breast cancer risk, indicating that the source of estrogen production is important.
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