In the past, diet and cancer associations primarily concentrated on the individual effects of nutrients on tumor growth. I personally conducted research with rats on the effects of polyunsaturated fatty acids on breast cancer incidence and we found no differences in tumor formation between omega-6 and omega-3 fats.
We have now gotten past this narrow approach and find that the study of overall diet patterns are a better way to convey the best way to counteract tumor initiation, promotion and progression.
The following article is long but contains excellent common sense information on diet and cancer prevention. It also explains why the scientific community has made these recommendations based on what we think we know from current research studies. It is one thing to know what to eat but the best is to know why recommendations are established.