Obesity and Cancer

by National Cancer Institute

Key Points

During the last two decades, the percentage of overweight and obese adults and children has been steadily increasing.

Lack of physical activity is strongly associated with obesity.

In addition to increasing the risk of coronary heart disease, stroke, high blood pressure, and diabetes, obesity increases the risk of cancers of the breast (postmenopausal), endometrium (the lining of the uterus), colon, kidney, and esophagus.

Avoiding weight gain can lower the risk of cancers of the breast (postmenopausal), endometrium, colon, kidney, and esophagus.

Regular physical activity lowers the risk of colon and breast cancers.

1. What is obesity?

People who are obese have an abnormally high and unhealthy proportion of body fat. To measure obesity, researchers commonly use a formula based on weight and height known as the body mass index (BMI). BMI is the ratio of weight (in kilograms) to height (in meters) squared. BMI provides a more accurate measure of obesity or being overweight than does weight alone.

Guidelines established by the National Institutes of Health (NIH) place adults age 20 and older into one of four categories based on their BMI:

<18.5
underweight
18.5 to 24.9
healthy
25.0 to 29.9
overweight
>30.0
obese

The following chart can be used to determine BMI category. (Find the height, and move across the chart to the appropriate weight.)

Compared with people in the healthy weight category, those who are overweight or obese are at greater risk for many diseases, including diabetes, high blood pressure, cardiovascular diseases, stroke, and certain cancers. Obesity lowers life expectancy.

2. How common is overweight or obesity?

Results from the 1999-2000 National Health and Nutrition Examination Survey (NHANES) show that an estimated 64 percent of U.S. adults are either overweight or obese. This represents an increase of 8 percentage points compared with the estimates from an earlier survey (NHANES III 1988-1994).

Nearly one-third of all adults are now classified as obese. This reflects an increase of 7.6 percentage points since 1994. The data show that 31 percent of adults age 20 and older-nearly 59 million people-have a body mass index (BMI) of 30 or greater, compared with 23 percent in 1994.

In addition, the percentage of children who are overweight continues to increase. Among children and teens ages 6 to 19, 15 percent (almost 9 million) are overweight according to the 1999-2000 data, or triple what the proportion was in 1980.

3. What causes obesity?

Experts have concluded that the chief causes of obesity are a sedentary lifestyle and overconsumption of high-calorie food:

Sedentary lifestyle — Researchers have found a strong correlation between lack of physical activity and obesity.

Diet — A diet high in calories and/or fat appears to be an important factor in obesity.

4. What have scientists learned about the relationship between obesity and cancer?

In 2001, experts concluded that cancers of the colon, breast (postmenopausal), endometrium (the lining of the uterus), kidney, and esophagus are associated with obesity. Some studies have also reported links between obesity and cancers of the gallbladder, ovaries, and pancreas.

Obesity and physical inactivity may account for 25 to 30 percent of several major cancers-colon, breast (postmenopausal), endometrial, kidney, and cancer of the esophagus.

Preventing weight gain can reduce the risk of many cancers. Experts recommend that people establish habits of healthy eating and physical activity early in life to prevent overweight and obesity. Those who are already overweight or obese are advised to avoid additional weight gain, and to lose weight through a low-calorie diet and exercise. Even a weight loss of only 5 to 10 percent of total weight can provide health benefits.

5. How many people get cancer by being overweight or obese? How many die?

In 2002, about 41,000 new cases of cancer in the United States were estimated to be due to obesity. This means that about 3.2 percent of all new cancers are linked to obesity.

A recent report estimated that, in the United States, 14 percent of deaths from cancer in men and 20 percent of deaths in women were due to overweight and obesity.

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