 However, the foods themselves are not necessarily carcinogenic, even if they contain trace amounts of carcinogens, because the gastrointestinal tract protects itself against carcinomas by shedding its outer layer continuously.Furthermore, detoxification enzymes, such as cytochromes P450 have increased activities in the gut for protection from food-borne toxins.Thus, in most cases, small amounts of B"a"P are metabolized prior to being passed into the blood.