n the last 25 years or so, people in the United States have become pro- gressively more overweight and obese. Today, about 65 percent of Americans are considered overweight and about one-third are obese, and the numbers of obese and overweight people keep rising. To check if you
are overweight or obese, see the body mass index table on page 101.
Also important is how one’s body fat is distributed. A disproportion- ate amount of body fat, especially if it is distributed around your waist area, creates an even greater risk of developing a range of health prob- lems, including high blood pressure, high blood cholesterol, diabetes, heart disease, and stroke. Research shows that an overweight or obese person’s heart muscle changes and pumps less effectively, even without evidence of heart disease.
Independent of any other factors, obesity seriously increases your risk of developing cardiovascular disease. Obesity is associated with high levels of “bad” LDL cholesterol and triglyceride levels, lower levels of “good” HDL cholesterol, higher blood pressure, and diabetes. It also harms your muscles and joints and increases your risk of certain kinds of cancers, including cancers of the breast, prostate, and colon.
Most people who are obese simply consume more calories than they burn off. It is most probably that combination of rich diet and lack of physical activity that has led to our epidemic of obesity in the United States. But other causes also contribute to the problem:

• Obesity tends to run in families. This is largely a result of shared lifestyle behaviors.
• Aging slows your metabolism, making it more dif?cult for your body to burn calories quickly, so you don’t need as many calories to maintain your weight. As we get older, we need to be concerned about calorie intake.
• Men burn more energy when they are at rest than women do, so they need more calories to maintain their weight. After meno- pause, a woman’s ability to burn calories decreases still more.
• Foods that are high in calories and fat but relatively low in nutri- tional value, served or purchased in excessively large portions, are a habit for many people.
• Lack of exercise is strongly related to obesity. More than two- thirds of Americans report no habitual physical activity.
• Childhood obesity tends to lead to adult obesity. Researchers think that the fat cells a person forms as a child remain into adult- hood. Dieting in adulthood decreases the fat-cell size rather than the number.
• Some illnesses such as an underactive thyroid or depression can cause obesity, but this occurs only rarely.

Body Mass Index

A useful way to estimate your body fat is a formula called the body mass index (BMI). The BMI is an assessment of your weight relative to your height and is a good indicator of the proportion of fat in most people’s bodies. You can calculate your BMI by multiplying your weight in pounds by 703, dividing by your height in inches, then dividing again by your height in inches. (For example, let’s say your weight in pounds is
140, and you are 67 inches tall. Multiply 140 by 703 to get 98,420. Divide that by 67 to get 1,468.95. Divide again by 67 to get 21.92. This is your BMI value.) Since these calculations are fairly complicated, see the convenient chart of body mass index by height and weight . According to the National Institutes of Health:
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• A BMI less than 18.5 is considered underweight.
• A BMI from 18.5 to 24.9 is considered normal. In this range you are at minimal risk of heart disease, provided you have no other risk factors.

• Some individuals are inappropriately classi?ed as overweight or obese due to large muscle mass or frame size.
• A BMI from 25.0 to 30.0 is of?cially classi?ed as overweight. In this range, your risk of cardiovascular disease increases slightly.
• A BMI of 30.0 or more is considered obese. Your risk level is high.

• A BMI of 40.0 is extreme obesity or morbid obesity. Your risk level is extremely high.

Waist CircumferenceAnother way to estimate body fat is by measuring your waistline. Your waist circumference is the measurement of your natural waist, just above your navel. A high-risk waistline is more than 35 inches for women and more than 40 inches for men, and indicates central obesity. Waist cir- cumference is a means of determining whether you tend to store fat around your waist (for an apple shape) or around your hips and thighs (for a pear shape). Apple-shaped people tend to have higher levels of “bad” cholesterol and triglycerides that clog arteries and raise the risk of heart disease.