Polyunsaturated fatty acids may enhance tumor growth not only by promoting cell proliferation but also by suppressing apoptosis , the process by which, normally, damaged cells die off. So both the amount and the type of fat consumed may count. Animal research and some population studies suggest that polyunsaturated fats increase risk. Monounsaturated fats may be protective. Polyunsaturated fats are found in safflower, sunflower, corn, and cottonseed oils.
Monounsaturated fats are in olive, canola, and peanut oils and most nuts.
Hydrogenated and Partially Hydrogenated Fats Polyunsaturated fats are unstable, and go rancid at room temperature. To stop this, food manufacturers add hydrogen molecules to the fat, a process known as hydrogenation. This converts the fats into trans-fatty acids, which are used in margarine and vegetable shortening, bakery products, peanut butter and snack foods. Trans-fatty acids are thought to be bad for the heart and may also be a factor in prostate cancer. Olive Oil Olive oil, used sparingly, is probably safe.