Of the Thousands of chemical we routinely encounter on a daily basis, most that enter our bodies are deliberately ingested because they are natural component of food.People who differ in the foods they eat also tend to differ in the cancer develop, suggesting that diet has an important influence on cancer risks. Unfortunately, the effects of individual foods ars diffecult to pinpoint because the eating habit of different people vary in numerous ways, making it hard to assess the impact of each ingredient. The situation is further complicated by the fact that in any given diet, the carcinogenic effect of a substance found in one type of food may be blocked by the protective action of another substance present in the same diet. in other word,cancer risk is related both to foods that increase cancer risk( whose intake should be reduced) and to foods that decrease cancer risk (whose intake should be increased)