Short of a causal relationship, new research shows strong correlation between fat content in the body and occurrence rates for certain types of cancer. "An increasing number of studies are finding that overweight and obese people are more likely to develop cancer of various kinds. At least half a dozen types of cancer are believed to be directly affected by weight. 'As time goes on, we're realizing that obesity is related to more cancers than we originally suspected,' said Dr. Donald Hensrud, an associate professor of preventive medicine and nutrition at the Mayo Clinic College of Medicine. Researchers are unable to prove that obesity actually causes cancer because requiring people to either gain weight or keep their weight down in clinical trials would be impossible. Most of the data come from observational studies, in which people who are thinner are probably doing many things differently than their heavier counterparts. Any number of those factors might be responsible for the difference in cancer rates."