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How do I know if I am obese?

Obesity is defined as an excess proportion of total body fat. Speak with your doctor if you are concerned about your weight and if you are attempting weight loss. You should call your doctor if you need help in losing weight or if you fall into either of these categories:

  • Body mass index (BMI): If your BMI is 30 or greater, you're considered obese and should talk to your doctor about losing weight for your health.
  • Waist circumference: If you have an "apple shape" — a "potbelly" or "spare tire" — you carry more fat in and around your abdominal organs. Fat in your abdomen increases your risk of many of the serious conditions associated with obesity. Women's waist measurement should fall below 35 inches. Men's should be less than 40 inches. If you have a large waist circumference, talk to your doctor about weight loss.

Can being overweight lead to medical problems?

Yes. Being overweight is linked to a number of health problems, including:

  • Heart disease and stroke
  • High blood pressure
  • Diabetes
  • Cancer
  • Gallbladder disease and gallstones
  • Osteoarthritis
  • Gout
  • Breathing problems, such as sleep apnea (when a person stops breathing for a short time during sleep) and asthma

Someone who is 40% overweight is twice as likely to die prematurely as an average-weight person. (This effect is seen after 10 to 30 years of being obese.)

Doctors generally agree that the more obese a person is, the more likely it is that he or she will have health problems. People who are 20% or more overweight can gain significant health benefits from weight loss. Many obesity experts believe that people who are less than 20% above their healthy weight should try to lose weight if they have any of the following risk factors.

  • Family history of certain chronic diseases: People with close relatives who have had heart disease or diabetes are more likely to develop these problems if they are obese.
  • Pre-existing medical conditions: High blood pressure, high cholesterol levels, or high blood sugar levels are all warning signs of some obesity-associated diseases.
  • "Apple" shape: People whose weight is concentrated around the abdomen may be at greater risk of developing heart disease, diabetes, or cancer than people of the same weight who are "pear-shaped."

Fortunately, even a modest weight loss of 10 to 20 pounds can bring significant health improvements, such as lower blood pressure and cholesterol levels.

What causes obesity?

In scientific terms, obesity occurs when a person's calorie intake exceeds the amount of energy he or she burns. What causes this imbalance between consuming and burning calories is unclear. Evidence suggests that obesity often has more than one cause. Environmental, psychological, genetic, and other factors all may play a part.

Environmental factors: A person's environment plays a significant role in weight status. Environment includes lifestyle behaviors, such as what a person eats and how active he or she is. Americans tend to have high-fat diets, often putting taste and convenience ahead of nutritional content when choosing meals. People can change what they eat and how active they are as a means of changing their weight status.

Psychological factors: Psychological factors also may influence eating habits. Many people eat in response to negative emotions such as boredom, sadness, or anger.

About 30% of those who seek treatment for serious weight problems have difficulties with binge eating. During a binge eating episode, people eat large amounts of food while feeling they can't control how much they are eating. Those with the most severe binge eating problems are considered to have what is called binge eating disorder. These people may have more difficulty losing weight and keeping the weight off than people without binge eating problems. Some will need special help, such as counseling or medication, to control their binge eating before they can successfully manage their weight.

Genetic factors: Obesity tends to run in families, suggesting that it may have a genetic cause. However, family members share not only genes but also diet and lifestyle habits that may contribute to obesity. Separating these lifestyle factors from genetic ones is often difficult. Still, growing evidence points to heredity as a strong determining factor of obesity. In one study of adults who were adopted as children, researchers found that their subjects' adult weights were closer to their biological parents' weights than their adoptive parents'. The environment provided by the adoptive family apparently had less influence on the development of obesity than the person's genetic makeup. However, many people genetically predisposed to obesity do not become obese or are able to lose weight and keep it off.

Other causes of obesity: Some illnesses can lower the metabolism or trigger an increased appetite which can cause obesity. These include hypothyroidism, Cushing's syndrome, depression, and certain neurologic problems. Certain drugs, such as steroids and some antidepressants, may cause excessive weight gain through the same methods. A doctor can determine if a patient has any of these conditions, which are believed to be responsible for only about 1% of all cases of obesity.