Epidemiological studies look at patterns of health and illness in individual populations.
There has been enormous growth in this field in recent years. Take, for example, the research on vegetable and fruit consumption alone. Panel scientists looked at more than 200 epidemiological studies and found convincing evidence that diets high in these foods decrease the risk of cancers of the mouth, pharynx, esophagus, lung, stomach, colon and rectum. Eating lots of fruits and vegetables probably also protects against cancers of the larynx, pancreas, breast and bladder. Differences in what the two groups eat provide clues about what could be causing or protecting against the specific cancer.