When organic plant or animal matter is burned, a number of toxic, mutagenic by-products are formed. Many of these by-products are exactly the same as those produced in the burning of tobacco that accounts for the toxic and cancer promoting effects of cigarettes. According to the National Cancer Institute, cancers of the colon, stomach and other digestive system malignancies are associated with high intake of charred or burned meats. While this effect has not yet been rigorously established for other burned foods such as burnt toast, the same effect is possible.