America has become a nation of chronically overweight people. Today approximately 65 percent of American adults are either overweight or obese, and 30.5 percent are obese, according to the U.S. Centers of Disease Control and Prevention. Between 1991 and 2002, the percentage of Americans who meet the criteria for obesity more than doubled. Moreover, the National Institutes of Health estimates that 34.7 million American women 20 years of age and older are obese. Why are these facts alarming?

Obesity (and unhealthy dietary habits and lifestyles that don’t include much or any physical activity) results in 300,000 preventable deaths each year in the U.S. and $100 billion in health care costs. Overweight people are more likely to have high blood pressure and high blood cholesterol, major risk factors for heart disease and stroke. Results of a large study supported by the U.S. National Heart, Lung, and Blood Institute (NHLBI) suggests that excess body weight is strongly and independently associated with an increased risk of heart failure.

As people become overweight, their glucose tolerance declines, putting them at twice the risk for developing type 2 diabetes. Diabetes is a major cause of early death, heart disease, kidney disease, stroke, blindness and amputation. Several types of cancer are associated with being overweight, including cancer of the uterus, gallbladder, cervix, ovary, breast and colon. Other conditions linked with obesity include sleep apnea, osteoarthritis, gout, gallbladder disease and infertility. Obesity-related conditions worsen as weight increases and often improve as the excess weight is lost.

Obesity is a major component of a group of metabolic risk factors known collectively as metabolic syndrome, or Syndrome X, including:

* Central obesity (too much fat tissue in and around the abdomen)

* High triglycerides and low HDL cholesterol, which both cause plaque accumulation in the arteries

* High blood pressure (130/85 mm HG or higher)Insulin resistance or glucose intolerance

* and several other conditions, called proinflammatory and prothrombotic states. Ask your health care professional for more information.

The underlying cause of metabolic syndrome is overweight/obesity, physical inactivity and genetic factors. People who have this syndrome are at increased risk for developing coronary heart disease, stroke, peripheral arterial disease and Type 2 diabetes.

Obesity is a complex disorder. It is caused by multiple factors, both environmental and inherited, including excessive calorie and food intake, decreased physical activity and genetic influences. The formula for weight gain is fairly straightforward, however. You gain weight when you consume more calories (energy) than your body uses or needs.

What’s the difference between being obese and being overweight? The defining characteristic in both overweight and obese people is excess body fat. The difference is a matter of degree.

Health care professionals use a simple calculation called the body mass index (BMI) to determine body weight relative to height. In adults, the BMI sum strongly correlates with total body fat content in adults. (See the Treatment section at this Web site for information on how to calculate BMI.) Overweight is defined as having a body mass index (BMI) between 25 and 29.9. Obesity is defined as having a BMI of 30 or more.

Where excess body fat is distributed on your body also plays a role in your risk for disease. Weight gain around your waist (specifically in your abdominal area) is more of a health risk because it is more metabolically active than weight gained on your hips and thighs. Excess abdominal fat is associated with an increase in blood cholesterol and insulin resistance, which may result in diabetes. An “apple shaped” figure may also raise your risks for other life-threatening illnesses, such as heart disease and stroke.