A high-meat, low-carbohydrate diet will also allow more aromatic amino acids, such as phenylalanine and tyrosine to enter the colon. Gut bacteria produce cresol and phenol when they metabolize these amino acids. Both cresol and phenol have been associated with the promotion of skin and colon cancer9 and rapid elimination of these compounds seems advisable, even if their effect on the gut mucosa has not been fully resolved. A diet rich in fibre can once again assist in clearance of these compounds by decreasing the food transit time. Amino acid metabolism will also increase the concentration of these compounds in the blood, and elimination of these compounds is normally done by the kidneys. Nevertheless, consistently high levels of these compounds can be associated with diets rich in animal products, as it is known that urinary phenol levels increase when subjects are fed high-meat diets and to decrease with an increase in dietary fibre.10 Low phenol levels could thus limit the risk of cancer, and a whole-food diet is ideal to achieve both low levels of these compounds and high levels of fibre.
Figure 4.7. The chemical structure of heterocyclic amines. (Adapt