Obesity - Causes

Part of the food we eat is "burned" to make energy. We use this energy to move, breathe, and carry out all our normal daily activities. The amount of energy present in food is measured in calories. If a person takes in more calories than his or her body burns up, the extra calories are stored in the form of fat.

There are other reasons why an individual's body might retain fat. Some people have a larger appetite than others. Their bodies seem to expect them to eat more often. For others, their bodies do not efficiently convert food to energy. They are more likely to convert the food they eat to fat.

Scientists now think that heredity is an important factor in obesity. That is, some people may inherit from their parents a genetic predisposition to gain weight. A genetic predisposition is a natural tendency over which a person has some, but not complete, control.

This theory has been supported by studies of adopted children. These children tend to have weight patterns more like those of their natural parents than those of their adoptive parents. This finding suggests that the children inherited from their natural parents the tendency to eat normally or excessively.

Even if people do inherit a tendency toward obesity, they do not necessarily have to become overweight. First, they can choose a diet that will reduce the risk of gaining weight. Some types of food, such as carbohydrates, are turned into energy more quickly than other types of foods, such as fats. A beneficial diet high in carbohydrates would consist of cereals, breads, fruits, and vegetables.

Second, a person can choose a lifestyle that will help burn up excess calories. A quiet lifestyle spent watching television will not burn up many calories compared with one that includes jogging, swimming, walking, or other forms of exercise.

Obesity can be caused by other factors as well. For example, a person may feel depressed (see depressive disorders entry) or have a low self-image. In response to those feelings, the person may eat more than his or her body really needs. The excess calories are converted to body fat.

The stage at which a person first becomes obese can affect his or her ability to lose weight. In childhood, excess calories are converted into new fat cells. Those fat cells remain in the child's body throughout life. In adulthood, excess calories simply cause existing fat cells to get larger. What this means is that obesity in childhood is especially serious. In some studies, people who became obese as children had up to five times as many fat cells as those who became obese as adults.

Obesity can also be caused by certain medical conditions. For example, hypothyroidism (pronounced HI-po-THIE-roi-DIZ-uhm) is a condition in which the thyroid gland does not function normally. The thyroid gland is responsible for the body's general level of activity. In hypothyroidism, the body's overall level of activity is reduced, causing fewer calories to be burned. As a result, the body tends to gain weight.

Consumption of certain drugs can also result in obesity. Steroids and antidepressants are examples of such drugs.