Everyone knows smoking causes cancer. Now it appears being fat increases your risk of dying from more than a dozen cancers.

An American Cancer Society study found that 90,000 cancer deaths in the United States each year could be prevented if no one were fat.

But while smoking rates have declined, obesity is increasing. About 65 percent of American adults are overweight, and 31 percent are obese.

Q. What cancers are we talking about?

A. Multiple myeloma, non-Hodgkin's lymphoma and cancers of the esophagus, colon and rectum, liver, gallbladder, pancreas and kidney in men and women; cancers of the stomach and prostate in men and cancers of the breast, uterus, cervix and ovary in women.

Q. Are there any cancers not affected by excess weight?

A. Yes. Melanoma and cancers of the brain and bladder.

Q. I'm overweight. How do I figure my risk?

A. Begin with your "body mass index," or BMI. Take your weight in pounds, divide it by your height in inches squared, then multiply by 703.

Q. That's too complicated.

A. Right. An easier way is to search the Internet for "BMI calculator." You will find sites that calculate your BMI; all you have to do is plug in your height and weight. Or, search for BMI tables. A BMI between 18.5 and 25 is normal. (Actually less/than equal 23...Click to Calculate your BMI here with this easy to use nomogram!)

Q. OK, I've figured out my BMI and it's over 25. How much does this increase my chance of dying of cancer?

A. In the overweight range (25-30 BMI), there's no increased risk for men and an 8 percent increase for women. In the obese range (30-35 BMI), there's a 9 percent increase in men and 23 percent increase in women. In the significantly obese range (35-40 BMI), there's a 20 percent increase in men and 32 percent increase in women. In the morbidly obese range (BMI of 40 or higher), there's a 52 percent increase in men and 62 percent increase in women.

Q. Why does obesity increase the risk of dying of cancer?

A. It increases levels of hormones such as estrogen and insulin, which raises cancer risks. Obesity can cause acid to flow from the stomach to the esophagus, increasing the risk of esophageal cancer. It can cause gallstones, increasing the risk of gallbladder cancer. And it makes it harder to diagnose and treat cancer.

Q. What foods should I eat to lower my cancer risk?

A. Limit saturated fat. Choose lean meats and low-fat dairy products, and substitute vegetable oils for butter or lard. Every day, eat at least five servings of fruits and vegetables, especially ones with the most color.

Q. Besides cancer, what are some other risks of obesity?

A. Heart attacks, strokes, high blood pressure and cholesterol, diabetes, gallstones, gout, arthritis, sleep apnea, incontinence, low self-esteem and depression.