Now a new study says that if Americans maintained a normal weight, an estimate 90,000 cancer deaths could be prevented each year.
Medical correspondent Dr. Emily Senay explained on The Early Show that a New England Journal of Medicine study shows a definite link between obesity and cancer.
About 900,000 people were studied for 16 years (the largest and longest research of its kind) and it found that most overweight women had a 62 percent higher death rate from cancer than women of normal weight. Excess weight accounts for about 20 percent of total cancer deaths in women.
The study also found that obesity is linked to particular cancers in women, such as cancer of the breast, cervix, uterus and ovaries.
Dr. Senay says being overweight is linked to cancer in women because excess body fat increases the amount of estrogen in the blood, which raises the risk of developing cancers of the reproductive system.
The study did find weight to play a smaller, but equally dangerous, role in promoting cancer in men. Overweight men had a 52 percent higher death rate from cancer, compared to normal weight men.
Excess weight accounts for about 14 percent of all cancer deaths in men. The main cancer affected by weight in men was prostate cancer.
Also, for men and women, excess weight can make it harder to find tumors. Some patients might not be able to fit into machines like CAT scans, which detect tumors, because of their large weight. It is also much harder for doctors to operate on the obese, Dr. Senay explains.
The research did find excess weight did not seem to play a role in cancers of the brain, skin and bladder.
The study did not observe any link between weight loss and lessening one's chances of getting cancer. However, she says, it's always a good idea to try and stay at a healthy weight because obesity has been linked to other health problems, such as heart disease and diabetes.