Last year the American Cancer Society asked people to list strategies for preventing cancer. Only 1 percent said "lose weight." Let's hope the other 99 percent heard last week's news. A huge ACS study has definitively linked obesity to a higher risk of getting and dying from a long list of cancers, including some--like prostate, ovarian and pancreatic cancers--that hadn't previously been connected. (It seems only melanomas, pediatric cancers and tumors of the brain, lung and bladder aren't weight-related.)
Exactly how obesity promotes tumor growth is unknown, but people with more fatty tissue do have higher levels of insulin and estrogen, which encourage cell division. Weight loss causes a drop in hormone levels, so it's extremely likely that it reduces cancer risk. To prove it, though, scientists would need to conduct another study using people who had successfully lost a lot of weight. The sad reason they haven't? "There aren't enough subjects," says lead author Jeanne Calle. For now, the ACS says the obese (technically, anyone with a body-mass index of more than 30) don't need more cancer screening. But it does suggest that they slim down. As if there weren't already enough reasons to do that.