A condition in which a person’s weight is much greater than what is considered healthy for his or her height. A person is medically classified as obese if he or she has a body-mass index (BMI) — a measure of weight relative to height — greater than or equal to 30. (People with a BMI of 25–29.9 are considered “overweight.”) According to the National Heart, Lung, and Blood Institute (NHLBI), overweight and obesity affect an estimated 97 million adults in the United States. People with obesity are at increased risk for developing a number of health problems, including Type 2 diabetes, coronary heart disease and stroke, certain types of cancer, sleep apnea, osteoarthritis, gallbladder disease, fatty liver disease, and pregnancy complications.

The causes of what is often called the “obesity epidemic” are much debated. The ready availability of high-calorie and processed foods, societal changes that discourage sit-down meals and walkable communities, and the growth in sedentary jobs have all been implicated in the rising obesity rate. In the simplest terms, obesity is caused by a person’s consuming more calories than he or she burns. The excess calories are turned into excess fat.

For people with obesity or overweight, even modest weight loss can have big health benefits. The loss of as little as 5% to 10% of body weight has been found to have the following effects:

  • Lower triglyceride levels, lower low-density lipoprotein (LDL, or “bad”) cholesterol levels, and higher high-density lipoprotein (HDL, or “good”) cholesterol levels
  • Lower blood pressure, which can decrease the risk of stroke
  • Lower blood glucose levels in people with Type 2 diabetes
  • Reduced symptoms of sleep apnea (a condition in which a person stops breathing and wakes up for brief periods during the night)
  • A lower risk of pregnancy complications

For people with arthritis in the joints of the lower body, including the hips, knees, lower back, and ankles, weight loss can reduce pain and improve function. A study has found that each pound of body weight exerts the force of 4 pounds on the knees. Losing as little as 10 pounds can thus have a significant effect on the pain and function of the knee joints.

There are several ways to address obesity, but the main two are diet and exercise. Lowering daily calorie intake is usually the most important change to the diet; people with obesity can get help developing a healthful eating plan from a registered dietitian. For exercise, the US Centers for Disease Control and Prevention recommends that all people get at least 150 minutes of moderate-intensity physical activity a week, along with muscle-strengthening exercise at least twice a week. In addition, behavior therapy, often undertaken with the help of a counselor, can help people address emotional barriers to weight loss and work their way out of unhealthful eating habits.

A final treatment option is weight-loss surgery, also known as bariatric surgery. Bariatric surgery is reserved for people who have not been able to lose enough weight through diet and exercise and who have a BMI of 40 or more (or 35 or more with serious obesity-related complications). There are three major types of bariatric surgery: gastric bypass, gastric banding, and sleeve gastrectomy. In gastric bypass, part of the stomach is closed off, creating a much smaller stomach to which the intestine is attached (thus allowing food to “bypass” most of the stomach and generally part of the intestine as well). In gastric banding, a band is placed around the stomach and tightened like a belt, creating a small opening between the two parts of the stomach. In sleeve gastrectomy, a large portion of the stomach is removed, creating a smaller, tube-shaped stomach that allows your body to absorb fewer nutrients. In all three procedures, the smaller upper part of the stomach or smaller stomach overall means that people are satisfied by less food. Still, people who have bariatric surgery must work to change their eating habits afterward to ensure good results.

People with obesity should discuss all possible treatments and decide on a weight-loss plan with their doctor.

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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