Obesity is caused by many factors. A person's weight is determined by a combination of genes, metabolism, behavior, culture, and environment. Genes and metabolism may help explain about 25 to 40 percent of body weight. However, a person's environment overwhelms the minor influences of biology. While genes may increase one's risk for obesity, they do not by themselves cause obesity. Genes certainly can't explain the rapidly increasing prevalence of obesity around the world.
For most people, obesity results from eating too much and not being active enough. The overwhelming factors responsible for obesity are environmental. Modern Western society encourages poor diets and lack of exercise. For example, portion sizes continue to increase. Americans were eating about 200 more calories per day in 2003 than they were in 1993. Fast-food restaurants encourage customers to "super size" and purchase "value" meals. Many target children, using well-known movie stars and cartoon characters in their advertising. Further, people eat out more often than in the past and many restaurants offer huge portion sizes. Americans seem determined to get as much food as they can for their money.
Television contributes to obesity through commercials urging people to buy food of low nutritional value, and by encouraging sedentary behavior. Many people tend to snack while watching television. Americans simply don't get enough physical activity. Less than one-third of American adults report that they do at least thirty minutes of brisk walking or other moderate activity on most days of the week, and almost half do no leisure-time activity at all. Almost half of U.S. high school students watch television more than two hours every day. This lack of physical activity is contributing to the increases in obesity and to other health-related conditions.
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