What Is Obesity?

From the WebMD Archives

Obesity means having far too much body fat. It's about much more than your clothing size or how you look. It can seriously affect your health.

Your whole body feels it, from your joints to your heart, blood pressure, blood sugar, and other systems. The extra fat cells produce inflammation and various hormones, which boosts your odds of chronic medical conditions.

If it seems like those odds are stacked against you, remember that it's possible to beat them. The first step is to know where you stand.

Are You Obese?

You step on the scale and your doctor or nurse notes your weight. They might also measure your waist, since it's especially risky to have too much belly fat.

If your doctor says you're overweight, that means "you're slightly over what's considered healthy," says Y. Claire Wang, MD. She's co-director of the Obesity Prevention Initiative at Columbia University.

Obesity is beyond being simply overweight. It's very common -- more than 1 in 3 U.S. adults are obese. If you're one of them, you can work to lose weight. Although it's not easy, dropping some of those extra pounds -- maybe fewer than you think -- starts to turn things around for you.

What Your BMI Says

For adults, experts usually define obesity based on body mass index, or BMI. This formula relates your weight to your height.

For instance, if two people weigh the same amount but one is taller than the other, the taller person will have a lower BMI. To find your body mass index, plug your height and weight into a BMI calculator.

If your BMI is:

  • Below 18.5: underweight
  • 18.5-24.9: normal
  • 25-29.9: overweight
  • 30 or higher: obese

If you're obese, your doctor might talk about the categories of obesity:

  • Obesity level l: BMI of 30-34.9
  • Obesity level ll: BMI of 35-39.9
  • Obesity level lll: BMI of 40 or higher, which some also call "morbid" obesity


Problems With BMI

Body mass index doesn't tell the whole story about your body, though.

For example, your BMI doesn't show whether your weight is fat or muscle. If you're a super-fit athlete, your muscle might put you in the "overweight" or "obese" range. Or, if you're elderly and have lost muscle mass over the years, your BMI could be normal, but you're not in as good shape as you think.

The formula also doesn't show where your fat is located on your body. And it doesn't consider differences among ethnic groups.

The CDC recommends that doctors use BMI a first step to screen adults for weight problems. Your doctor should also consider other things, like how fit you are.

Check Your Waist Size

Get a tape measure and wrap it around your belly.

If your waist is more than 35 inches around and you're a woman, or if it's more than 40 inches and you're a man, you might have too much belly fat.

Research shows that carrying extra fat around your stomach is unhealthy, no matter what your BMI is.

The Edmonton Scale

Obesity experts also use the Edmonton obesity staging system. It takes BMI a step further by relating it to your health. There are five stages:

Stage 0: You don't have any health problems related to your weight.

Stage 1: Any weight-related health problems are mild (such as borderline high blood pressure or occasional aches and pains).

Stage 2: You have an obesity-related chronic disease, such as high blood pressure, type 2 diabetes, sleep apnea, or osteoarthritis, and you have moderate problems doing daily activities or feeling well.

Stage 3: You've had serious weight-related problems, such as a heart attack, heart failure, stroke, or other conditions.

Stage 4: This is the most severe level of weight-related chronic health conditions, which are extreme and life-threatening.

If your doctor doesn't use this system, ask them to tell you how your weight is affecting your health.

What Obesity Does to Your Body

"When people become obese we start to see disease rates go way up," Wang says.


Adam Tsai, MD, of Kaiser Permanente Colorado and a spokesman for the Obesity Society, agrees. "The risks go up and up as BMI increases," he says.

Obesity puts extra stress on your bones, joints, and organs, making them work harder than they should. Too much body fat raises your blood pressure and cholesterol, and makes heart disease and stroke more likely. It also worsens conditions like osteoarthritis, back pain, asthma, and sleep apnea.

Too much fat causes inflammation that can damage cells. Obesity is also linked to several types of cancers. It can also make your body respond less well to insulin, which controls your blood sugar. Over time, that can lead to type 2 diabetes.

The weight makes it harder to be active, too. "Carrying around extra pounds takes extra energy, so it can be difficult for obese people to exercise," Tsai says.


If you think calories are the only thing that matters, think again.

No doubt: Calories definitely count. But so do a lot of other things, like whether you can afford healthy foods and can easily use parks, sidewalks, or other places where you can be active.

"For many people, it's not an individual choice," Wang says.

Your emotions, and how you handle them, also matter. Many people eat when they're mad, sad, bored, or stressed. Weight problems can add to that. If you feel badly or are self-conscious about your body, that can hold you back from the full life that people of all sizes deserve. In turn, you eat more, seeking comfort.

Obesity can run in families, too. Your genes might be part of the reason. And you probably got your lifestyle and eating habits from your family, too. You can change those habits, though.

Your friends also count. Some research shows that obesity is "contagious" socially. In one study of some 12,000 people, Harvard researchers found that if someone gains weight, their family, friends, and partners also tend to gain weight, even if they don't live near each other. Their influence affects you.

Also, you might've heard about studies that show links to air pollution, viruses, exposure to certain chemicals, or even the bacteria in a person's gut. But they don't prove that those things cause obesity.

"There's a lot we still don't know," but it's clearly not just about self-control, Wang says.


Why Change Is Tough -- and What Helps

If you've tried to lose weight before, you know it's much easier said than done. It's not just about willpower, and the solutions go way beyond counting calories, fat grams, or carbs.

Think about it: What you eat and how active you are affects your whole day. You'll need to makeover the habits that go into your meals, snacks, and activities.

That's a huge commitment. Take it one small step at a time. You can build on successes. Don't try to do too much, too soon.

If you often eat for emotional reasons, you'll need to find other ways to handle the feelings that usually make you eat. Consider talking with a counselor. They can help you make those shifts in how you think, and how you relate to food and to your body.

Meanwhile, your body might resist your weight-loss efforts.

"If someone does lose 20 or 30 pounds, their metabolism goes down and they start to burn fewer calories," Tsai says. "Our bodies are designed to regain weight, so it's much easier to prevent obesity than to treat it."

Take the First Step

Even if you've been at your current weight for a long time, "if you're committed to getting healthier, there's almost certainly a treatment that can work," Wang says.

A great first step is to partner with your doctor. If he don't bring up the topic, make the first move and let them know that you want to work toward a healthier weight. Ask for advice, or for a referral to another doctor with more experience in this area. You might also want a referral to a nutritionist and a certified fitness trainer.

Before you start to make changes, write down everything you eat and drink for a few days. This can help you decide what you need to change about your diet.

Most people, at any weight, need to eat more fruits, vegetables, and lean proteins. They also need to cut out junk food and sugary drinks, Wang says.

Being active is also key. Any kind of movement helps, and you don't have to go to a gym. Ask your doctor what's OK for you to do. A certified personal trainer can help you plan a workout that fits your needs.


If you find that you need more help than diet and exercise, talk with your doctor. Certain prescription drugs are approved for weight loss. They curb your appetite or prevent your body from absorbing fat. You'll still need to watch what you eat and be active.

Weight loss surgery can help people lose large amounts of weight. But it's not right for everyone, and it does have risks. You won't be able to eat like you used to, you might need to take vitamins to meet your nutritional needs, and you'll need to work on diet and exercise to keep up the results.

Keep Your Perspective

If it all seems like too much to take on, or if your past tries to lose weight make you wonder if it will ever happen for you, take a moment to challenge those thoughts.

It's not about being a certain size. It's about small steps that add up to better health over time.

If you lose as little as 5% to 10% of your weight, it starts to make a positive difference.

Focus on what is possible for you and what you can commit to, even if it's just for right now. You can make the decision again tomorrow and build your way to where you want to be, day by day.

WebMD Feature Reviewed by Michael Dansinger, MD on December 23, 2014



National Heart, Lung, and Blood Institute: "How Are Overweight and Obesity Diagnosed?"

CDC: "About BMI for Adults," "Body Mass Index: Considerations for Practitioners," "Genomics and Health," and "Losing Weight."

University of Rochester Medicine: "What Is Morbid Obesity?"

Harvard School of Public Health: "Obesity Prevention Source."

American Heart Association: "Obesity Information."

Ramos-Nino, M. ISRN Oncology, Volume 2013.

National Diabetes Information Clearinghouse: "Causes of Diabetes."

NIH Curriculum Supplement Series: "Information on Energy Balance."

Brochu, P. Risk Analysis, March 2014.

Gabbert, C. Pediatrics, October 2010.

Thayer, K. Environmental Health Perspectives, June 2012.

Sans, Y. Pharmacological Research, March 2013.

Weight Control Information Network: "Prescription Medications for the Treatment of Obesity."

News release, FDA.

University of California San Francisco Medical Center: "Bariatric Surgery."

Padwal, R. Canadian Medical Association Journal, Oct. 4, 2011.

Christakis, N. The New England Journal of Medicine, July 26, 2007.

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