OBESITY AND HORMONES
Hormones are one factor in obesity. The hormones leptin, insulin, sex
hormones and growth hormone influence appetite, metabolism and body fat
distribution. Obese people have levels of these hormones that encourage abnormal
metabolism and the accumulation of body fat.
The endocrine system is made up of glands that secrete hormones into the
bloodstream. Hormones are chemical messengers that regulate body processes. The
endocrine system works with the nervous system and the immune system to help the
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
Leptin, the fat hormone
The hormone leptin is produced by fat cells and is secreted into the
bloodstream. Leptin reduces appetite by acting on specific centres of the brain
to reduce the urge to eat. It also seems to control how the body manages its
store of body fat. Since leptin is produced by fat, leptin levels tend be higher
in obese people than in people of normal weight.
The issue being researched at the moment is why obese people are obese,
considering they have higher than usual levels of an appetite-reducing hormone.
One theory is that obese people aren't as sensitive to the effects of leptin.
Research is focusing on why leptin messages aren't getting through to the brain
in obese individuals.
Leptin and dieting
Various studies have shown that blood leptin levels drop after low-kilojoule
diets. Reduced leptin levels may increase appetite and slow metabolism. This may
help to explain why crash dieters usually regain their lost weight. It is
possible that leptin therapy may one day help dieters to maintain their weight
loss in the long term, but more research is required before this becomes a
Insulin is a hormone produced by the pancreas and important for the regulation
of carbohydrate and fat metabolism. Insulin stimulates glucose uptake from the
blood in tissues such as muscle, liver and fat. This is an important process to
ensure energy is available for everyday functioning and to maintain normal
levels of circulating glucose.
In obesity, 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
the metabolic syndrome.
The sex hormones
Body fat distribution plays an important role in the development of
obesity-related conditions such as heart disease, stroke and some forms of
arthritis. Abdominal fat is a higher risk factor for disease than fat stored on
the bottom, hips and thighs.
It seems that oestrogens help to decide body fat distribution. Oestrogens are
sex hormones made at highest amounts by the ovaries. They are responsible for
prompting ovulation every menstrual cycle. Men and postmenopausal women do not
produce substantial amounts of gonadal oestrogens, instead, the main site of
oestrogen production becomes the fat, albeit at much lower amounts than what is
produced in premenopausal ovaries. In younger men, androgens are produced at
high levels in the testes. As they get older, levels gradually decrease.
These changes in sex hormone levels with age in both men and women are
associated with notable changes in body fat distribution. While women of
childbearing age tend to store fat in the lower body (‘pear-shaped’), older
men and postmenopausal women tend to increase storage of fat around the abdomen
(‘apple-shaped’). Postmenopausal women on oestrogen supplements don’t
accumulate fat around the abdomen. Animal studies have also shown that a lack of
oestrogen leads to excessive weight gain.
The pituitary gland in the brain produces growth hormone, which influences an
individual’s height and contributes to bone and muscle building. Growth
hormone also affects metabolism (the rate at which kilojoules are burned for
energy). Researchers have found that growth hormone levels in obese people are
lower than those in people of normal weight.
Obesity hormones as a risk factor for disease
Obesity is associated with the increased risk of developing a number of
diseases, including cardiovascular disease, stroke, several types of cancer, and
with a decreased longevity and quality of life. For example, the increased
production of oestrogens in the fat of obese older women is associated with an
increase in breast cancer risk, indicating that the source of production is
Behaviour influences these hormones
Obese people have hormone levels that encourage the accumulation of body fat. It
seems that behaviours such as overeating and lack of regular exercise, over
time, ‘reset’ the processes that regulate appetite and body fat distribution
to make the person physiologically more inclined to gain weight.
The body is always trying to maintain balance, so it resists any short-term
disruptions such as crash dieting. However, there is evidence to suggest that
long-term behaviour changes, such as healthy eating and regular exercise, can
retrain the body to shed excess body fat and keep it off. Weight loss is also
associated with a decreased risk of developing heart disease, stroke, type II
diabetes and cancer.
- The hormones leptin, insulin, oestrogens and androgens, and growth hormone
influence appetite, metabolism and body fat distribution.
- Obese people have hormone levels that encourage the accumulation of body
- Obesity is a risk factor for disease.
- Obesity-related disease is preventable with weight loss