By Lin Yan

Overweight and obesity are talked about often in the U.S. Most Americans (83 percent ) recognize the link between being overweight and heart diseases and many (57 percent) know about the link between being overweight and diabetes, according to a survey commissioned by the American Cancer Society. But far fewer (8 percent) know there is a connection between being overweight and cancer.

Body mass index (the ratio of weight to height) is the most commonly used measurement to determine whether a person is overweight. A BMI score of 18.5 to 24.9 indicates a healthy weight, 25 to 29.9 is overweight, and 30 and higher is obese. It is estimated that two-thirds of American adults are either overweight or obese, and nearly one-third of all adults now are classified as obese. Furthermore, the percentage of children who are overweight continues to increase. Among children and teenagers ages 6 to 19, 15 percent (almost 9 million) are overweight.

Obesity is related to several major types of cancers. A recent study showed that cancers of the colon, breast (postmenopausal), endometrium (the lining of the uterus), kidneys and esophagus are related to obesity. In 2002, about 41,000 new cases of cancer were diagnosed in the U.S. About 3.2 percent were estimated to be because of obesity.

It also is estimated that overweight and obesity account for 14 percent of deaths from cancer among men and 20 percent among women in the U.S.

Biological mechanisms that explain how obesity increases cancer risk may be different for different cancers. However, a possible mechanism may be related to alternations in production of sex hormones. Adipose cells produce sex hormones (for example, estrogen) and other hormonelike compounds that promote cell division and proliferation, which may stimulate abnormal development and growth.

The major causes of overweight and obesity are sedentary lifestyles and overeating high-calorie foods.

Some modern conveniences actually contribute to this weight gain. For example, many people spend long hours in front of computers and televisions, cars reduce our need to expend physical activity, and access to inexpensive processed foods is easy. In fact, if we consume just 100 calories more than we burn each day, we will put on a pound in a little more than a month, and almost 30 pounds in three years.

High-calorie foods tend to be high in fat and sugars and low in fiber. The best examples are traditional fast foods, such as pizza, cheeseburgers, fried chicken, french fries and ice cream. Most processed foods also are high in calories because fat and sugar often are added to enhance texture and taste. Meats, milk, cream, yogurt and eggs also can be high in calories — though low-fat or lower-calorie choices can be made.

We can maintain a healthy weight by consuming fewer calories and burning more.

The best way to reduce high-calorie foods is to increase the proportion of low-calorie foods on our plate — namely vegetables, fruits, beans and whole grains. Plant foods are high in fiber and water and tend to fill us up because of their bulk, but not their calories. They include cruciferous and dark green leafy vegetables, tomatoes, berries, grapes and grape juice, beans, soy and whole grains. It is recommended that two-third of our plate should hold vegetables, fruits, beans and whole grains and one-third hold animal proteins.

Logging long hours at a gym or playing sports is not the only way to be physically active. For example, 30 minutes of light gardening or yardwork uses 165 calories, and a 30-minute walk burns 140 calories. It is recommended to engage in at least 60 minutes of moderate activity or 30 minutes of vigorous activity daily.

It’s estimated that 30 percent to 40 percent of cancers are related directly to lifestyle. Eating healthy foods and staying physically active can help us manage a healthy weight and protect against cancer.

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