Apart from increased intake of energy rich foods and decreased exercise and physical activity, hormones and genes also play a role in obesity and overweight.
Several hormones including leptin, insulin, sex hormones and growth hormone have been studied extensively for their role in obesity and increase in body weight. These hormones play a role in appetite, metabolism, body fat distribution and increased storage of excess energy in food as fats.
Obese people have levels of these hormones that can increase accumulation of body fat by altering the metabolism of the fats.
The endocrine system
The endocrine system comprises of glands that secrete hormones into the bloodstream. These hormones are chemical messengers that regulate body processes. The release of these hormones is regulated by the nervous system as well as the immune system that helps the body cope with stresses and other situations.
While some hormones that are released during stresses help the body prepare for an emergency by making available stored and taken energy, yet others help body store energy as fats.
Thus excesses or deficits of hormones can lead to obesity. In addition, obesity also results in changes in certain hormone levels as well.
Some of the hormones important in the pathology of obesity include:-
Leptin is released from the adipocytes in amounts proportional to the body weight. This hormone reaches the brain and binds with its receptors and plays a role in body’s capacity to use and store energy.
In the long term it leads to decrease in appetite and an increase in heat generation from energy both leading to a decrease in obesity.
Since leptin is produced by fat cells, the levels of the hormone tend be higher in obese people than in people of normal weight.
However despite these high level, obese people are not sensitive to the effects of leptin and thus do not have a reduced appetite. This could be due to deficiency of leptin receptors in these individuals.
Insulin is a hormone produced by the pancreas. It helps regulate carbohydrate and fat metabolism and reduces blood glucose after a meal. Insulin stimulates glucose uptake from the blood by the muscles, liver, fats and tissues for utilization.
In obesity, insulin signals are lost and there is rise in blood levels of glucose despite high or normal levels of insulin. This is called insulin resistance. Insulin resistance is the hallmark feature of type 2 diabetes and the metabolic syndrome.
Body fat distribution is regulated by estrogens and androgens (female and male sex hormones respectively). While estrogens are secreted by ovaries, androgens are made and secreted by testes.
In men, and in women who have had menopause, the main site for estrogen production is fat cells. Estrogens allow for fat distribution to the lower body or pear shape.
Abdominal fat is a higher risk factor for disease than fat stored on the bottom, hips and thighs or lower fat distribution.
These changes in sex hormone levels after menopause and in obese individuals thus change the fat distribution. Older men and postmenopausal women, unlike women of reproductive age, tend to increase storage of fat around the abdomen (apple shape). this increases their risk of disease.
The pituitary gland in the brain produces growth hormone. This helps in growth of a child. Growth hormone also affects metabolism of all the nutrients taken by the body. Levels of growth hormone are lower in obese people than normal individuals.