Excess body fat leads to reduced life expectancy and/or increased health problems. Obesity increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, breathing difficulties during sleep, certain types of cancer, diabetes mellitus type 2, high blood pressure, high blood cholesterol and osteoarthritis.

Health consequences fall into two broad categories: those attributable to the effects of increased fat mass (such as osteoarthritis, difficulties during sleeping, social stigmatization) and those due to the increased number of fat cells (diabetes, cancer, cardiovascular disease, non-alcoholic fatty liver disease). Increases in body fat alter the body's response to insulin, potentially leading to insulin resistance.

Obesity is one of the leading preventable causes of death worldwide. On average, obesity reduces life expectancy by six to seven years.
The generally accepted view is that being overweight causes similar health problems to obesity, but to a lesser degree. It is estimated that the risk of death increases by 20 to 40 percent among overweight people.

Causes

Being overweight is generally caused by the intake of more calories (by eating) than are expended by the body (by exercise and everyday living). Factors which may contribute to this imbalance include:

Limited physical exercise and sedentary lifestyle

Overeating

Poor nutrition

Alcoholism

Stress

Insufficient or poor-quality sleep

Smoking cessation and other stimulant withdrawal

Treatment

The primary treatment for obesity and overweight is dieting and physical exercise. Diet programs may produce weight loss over the short term, but keeping this weight off can be a problem and often requires making exercise and a lower calorie diet a permanent part of a person's lifestyle. In addition health supplements may be taken to reduce appetite or inhibit fat absorption.

Dieting

Diets to promote weight loss are generally divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie. Very low calorie diets provide 200–800 kcal/day, maintaining protein intake but limiting calories from both fat and carbohydrates. They subject the body to starvation and produce an average weekly weight loss of 1.5–2.5 kilograms (3.3–5.5 lb). These diets are not recommended for general use as they are associated with adverse side effects such as loss of lean muscle mass, increased risks of gout, and electrolyte imbalances. People attempting these diets must be monitored closely by a physician to prevent complications.

Exercise

With use, muscles consume energy derived from both fat and glycogen. Due to the large size of leg muscles, walking, running, and cycling are the most effective means of exercise to reduce body fat. Exercise affects macronutrient balance. During moderate exercise, equivalent to a brisk walk, there is a shift to greater use of fat as a fuel. A minimum of 30 minutes of moderate exercise at least 5 days a week is recommended.

Warning

The health benefits of weight loss are also somewhat unclear. While it is generally accepted that for significantly obese patients, losing weight can reduce health risks and improve quality of life, there is some evidence to suggest that for merely overweight patients, the health effects of attempting to lose weight may actually be more detrimental than simply remaining overweight. Moreover, for all individuals, repeatedly losing weight and then gaining it back, is believed to do more harm than good and can be the cause of significant additional health problems. This is caused by the loss of more muscle than fat.