Obesity can be hereditary, hence some people are at increased risk. However, obesity only develops from overeating, irregular meals and lack of daily physical activity. Many people think that when a disease is hereditary, it is inevitable that you will suffer from the condition but this is not true.

Besides genes, food and physical activity, it is possible that other so far unknown elements may play a part.

Factors that increase your risk of carrying more weight than is healthy include:

Diet
Regular consumption of high-calorie foods, such as fast foods, contributes to weight gain. High-fat foods are dense in calories. Loading up on soft drinks, candy and desserts also promotes weight gain. Foods and beverages like these are high in sugar and calories.

Inactivity
Sedentary people are more likely to gain weight because they don't burn calories through physical activities.

Psychological factors
Some people overeat to cope with problems or deal with difficult emotions.

Genetics
If one or both of your parents are obese, your chances of being overweight increase by 25 percent to 30 percent. Your genes may affect the amount of body fat you store and where that fat is distributed. But, your genetic makeup doesn't guarantee that you'll be obese.

Sex
Men have more muscle than women do, and because muscle burns a greater number of calories than fat burns, men expend up to 20 percent more calories than women do even at rest. So for women, achieving a healthy weight may be a tougher challenge.

Age
As you get older, the amount of muscle in your body tends to decrease, and fat accounts for a greater percentage of your weight. This lower muscle mass leads to a decrease in metabolism. Your metabolism also slows naturally with age. In addition, people tend to be less active as they age. Together, these changes reduce calorie needs. If you don't decrease your caloric intake as you age, you'll likely gain weight.

Cigarette smoking
Smokers tend to gain weight after quitting. A 6- to 8-pound weight gain isn't uncommon. This weight gain may be partially due to nicotine's ability to raise the rate at which your body burns calories (metabolic rate). When smokers stop, they burn fewer calories. Smoking also affects taste. Former smokers often gain weight because they eat more after they quit. Their food tastes and smells better.

Pregnancy
After each pregnancy, a woman's weight increases an average of 4 to 6 pounds over her pre-pregnancy weight. This weight gain may contribute to the development of obesity in women.

Medications
Corticosteroids and tricyclic antidepressants, in particular, can lead to weight gain.
Medical problems. Less than 2 percent of all cases of obesity can be traced to a medical cause, such as low thyroid function, excess production of hormones by the adrenal glands (Cushing's syndrome) or other hormonal

Imbalances
A low metabolic rate is rarely a cause of obesity. A medical problem can also lead to decreased activity, which can result in weight gain.