The 1997 report, Food, Nutrition and the Prevention of Cancer: a Global Perspective, by the World Cancer Research
Fund and the American Institute for Cancer Research uses key words to summarize the body of scientific evidence.
These key words are:

Convincing: "epidemiological studies show consistent associations, with little or no evidence to the contrary. There should be a substantial number of acceptable studies, (that is, for dietary variables more than 20 studies) preferably including prospective designs, conducted in different population groups, controlled for possible confounding factors. Dietary intake data should refer to time preceding occurrence of cancer. Any dose-response relationships should be supportive of a causal relationship. Associations should be biologically plausible. Laboratory evidence is usually supportive or strongly supportive."
Probable: "epidemiological studies showing associations are either not so consistent, with a number and/or proportion of studies not supporting the association, or else the number or type of studies is not extensive enough to make a more definite judgement. Mechanistic and laboratory evidence are usually supportive or strongly supportive."
Possible: "epidemiological studies are generally supportive, but are limited in quantity, quality or consistency. There may or may not be supportive mechanistic or laboratory evidence. Alternatively, there are few or no epidemiological data, but strongly supportive evidence from other disciplines"
Insufficient: "there are only a few studies, which are generally consistent, but really do no more than hint at a possible relationship. Often, more well-designed research is needed."

EXTOXNET FAQS Diet and Cancer Homepage

Prepared 1998 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.