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Obesity is a term used to describe body weight that is much greater than what is healthy. If you are obese, you also have a much higher amount of body fat than is healthy or desirable.

Adults with a body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) between 25 kg/m2 and 30 kg/m2 are considered overweight.

Adults with a BMI greater than or equal to 30 kg/m2 are considered obese.

Anyone who is more than 100 pounds overweight or who has a BMI greater than or equal to 40 kg/m2 is considered morbidly obese.

Alternative Names

Morbid obesity; Fat - obese


Taking in more calories than you burn leads to being overweight and, eventually, obesity. The body stores unused calories as fat. Obesity can be the result of:

  • Eating more food than your body can use
  • Drinking too much alcohol
  • Not getting enough exercise

An underactive thyroid (hypothyroidism) may lead to 5 - 10 pounds of weight gain. Some antidepressants and antipsychotic medicines may also contribute to weight gain and obesity. Genetic factors play some part in the development of obesity -- children of obese parents are 10 times more likely to be obese than children with parents of normal weight.

People who are at higher risk for obesity include:

  • Lower income groups
  • Former smokers
  • People with chronic mental illness
  • People with disabilities
  • People with a sedentary lifestyle
Signs and tests

The health care provider will perform a physical exam and ask questions about your medical history, eating habits, and exercise routine.

Skin fold measurements may be taken to check your body fat percentage.

Blood tests may be done to look for thyroid or endocrine problems, which could lead to weight gain.

Support Groups

Many people find it easier to follow a diet and exercise program if they join a group of people with similar problems.

See: Eating disorders - support group

Calling your health care provider

Schedule an appointment with your health care provider if you or your child is obese or gaining weight at an extremely rapid rate. Remember that catching the problem early is much simpler than trying to fix it after the person has gained an excessive amount of weight.


Obesity is a significant health threat. The extra weight puts added stress on all parts of your body.

Medical problems commonly resulting from untreated obesity and morbid obesity include:

Extreme obesity can lead to a gradual decrease in the level of oxygen in your blood, a condition called hypoxemia. Decreased blood oxygen levels and sleep apnea may cause a person to feel sleepy during the day. These conditions may also lead to high blood pressure and pulmonary hypertension. In extreme cases, especially when left untreated, this can lead to right-sided heart failure and ultimately death.


Regular exercise and a healthy diet are crucial when it comes to controlling your weight. Although there are many programs advertised to help you lose weight, the only method proven safe over the long-term is to burn more calories than you consume.

Exercising and eating right must become as much a part of your routine as bathing and brushing your teeth. Unless you are convinced of the benefits, you will not succeed.


Most people can lose weight by eating a healthier diet and exercising more. Even modest weight loss can improve your health. Sticking to a weight reduction program is not easy. You will need a lot of support from family and friends.

When dieting, your main goal should be to learn new, healthy ways of eating and make them a part of your everyday routine. Learn to read the nutrition labels and ingredients of all the foods you eat.

Work with your health care provider and dietitian to set realistic, safe daily calorie counts that help you lose weight while staying healthy. Remember that if you drop pounds slowly and steadily, you are more likely to keep them off. Your dietitian can teach you about healthy food choices, portion sizes, and new ways to prepare food.

Extreme diets (fewer than 1,100 calories per day) are not thought to be safe or to work very well.

  • These types of diets often do not contain enough vitamins and minerals.
  • People who are on these diets may experience symptoms such as fatigue, feeling cold most of the time, hair loss, or dizziness.
  • There is a risk for gallbladder stones, changes in menstrual periods, and rarely, dangerous heart rhythms.
  • Most people who lose weight this way return to overeating and become obese again.

See also: Sweeteners

Other changes can have an impact on your weight loss success:

  • Eat only at the table. No snacking in front of the TV, in bed, while driving, or while standing in front of the open refrigerator.
  • Learn about appropriate portion sizes.
  • Choose low-calorie snacks, such as raw vegetables.
  • Learn new ways to manage stress, rather than snacking. Examples may be meditation, yoga, or exercise.
  • Keep a diet and exercise journal. This may help you identify overeating triggers in your life.
  • If you are depressed, seek medical treatment rather than eating excessively to help cope with your depression.
  • Find a support group or consider psychotherapy to help you achieve your weight loss goal.


To lose weight, you must burn more calories than you eat. Exercise is a key way to do this. Walking a mile a day for 30 days will help you burn off 1 pound of fat, as long as you don't eat more than usual.

If you have not been active, start slowly and build up over weeks or even months. Walking can be a good exercise to start with. Talk to your health care provider before starting.

Every week, increase the amount of time you spend doing the activity. Do it more often or add a second activity. You can increase the speed or difficulty of the activity (for example, by going up hills).

All adults should get 2 1/2 hours of aerobic exercise each week. Spread the exercise out over the week. Exercise for at least 10 minutes at a time.

Find ways to increase your activity level very day.

  • Walk instead of driving. If you have to drive, park several blocks away from your destination.
  • Climb stairs instead of using an elevator or escalator.
  • Do other house activities, such as gardening.

In addition to burning off extra calories, exercise will also:

  • Lift your mood and help with anxiety
  • Make your bones stronger
  • Reduce your chance of having a heart attack or stroke
  • Help you manage high blood pressure and cholesterol


There are many over-the-counter diet products. These include herbal remedies. Most of these products do not work and some can be dangerous. Before using an over-the-counter or herbal diet remedy, talk to your health care provider.

Several prescription weight loss drugs are available, including sibutramine (Meridia) and orlistat (Xenical). Ask your health care provider if these are right for you.

Usually, you can lose between 5 and 10 pounds by taking these drugs. People usually regain the weight when they stop taking the medication, unless they have made lasting lifestyle changes.


Weight-loss surgery may be done to help you lose weight if you are very obese and have not been able to lose weight with diet and exercise.

Surgery alone is not the answer for weight loss. It can train you to eat less, but you still have to do much of the work. You must be committed to diet and exercise after the surgery.Talk to your doctor to learn if this is a good option for you.

The two most common weight-loss surgeries are:

  • Laparoscopic gastric banding -- the surgeon places a band around the upper part of your stomach, creating a small pouch to hold food. The band helps you limit how much food you eat by making you feel full after eating small amounts.
  • Gastric bypass surgery -- helps you lose weight by changing how your stomach and small intestine handle the food you eat. After the surgery, you will not be able to eat as much as before, and your body will not absorb all the calories and other nutrients from the food you eat.

You may have complications from these surgeries. One problem some people have is throwing up if they eat more than their new small stomach can hold.


Leslie D, Kellogg TA, Ikramuddin S. Bariatric surgery primer for the internist: keys to the surgical consultation. Med Clin North Am. 2007;91:353-381.

Richards WO, Schirmer BD. Morbid Obesity. In: Townsend CM Jr., Beauchamp RD, Evers BM, Mattox KL, eds. Sabiston Textbook of Surgery. 18th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 17.

Gardner CD, Kiazand A, Alhassan S, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA. 2007;297(9):969-977.

Position of the American Dietetic Association: Weight Management. J Am Diet Assoc. 2009;109:330-346.

Thompson WG, Cook DA, Clark MM, et al. Treatment of obesity. Mayo Clin Proc. 2007;82(1):93-101

Svetke, LP, Stevens VJ, Brantley PJ, et al. Comparison of strategies for sustaining weight loss: the weight loss maintenance randomized controlled trial. JAMA. 2008;299(10):1139-48.

Kaplan LM, Klein S, Boden G, Brenner DA, Gostout CJ, Lavine JE, Popkin BM, Schirmer BD, Seeley RJ, Yanovski SZ, Cominelli F. Report of the American Gastroenterological Association (AGA) Institute Obesity Task Force. Gastroenterology. 2007;132(6):2272-5.

Related Taxonomy

Review Date: 6/14/2010
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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