Or they may be part of meals that contain high-fat items, such as some types of cheese. Most of the studies examined the dietary differences between people with cancer and those without. In many cases, the primary difference was the consumption of tomatoes or tomato products, or the presence in the blood of high levels of lycopenes. One study, for instance, showed a 50 percent reduction in oral cancer when comparing people who averaged one tomato a day with people who ate less than three a week. The most prominent of these phytochemicals is a compound that leads to the formation of carotenoids, chemicals that can protect cells from the effects of oxidants.
Tomatoes are a particularly rich source of several carotenoids, including lycopene.
However, Giovannucci wrote that lycopene's benefits as a supplement, such as in a vitamin pill, have not been proven. The lowered cancer risk has been demonstrated only for raw or processed tomatoes, not from compounds extracted from the fruit.