Within the gut, the limited availability of carbohydrates in high-meat diets will lead to an increase in ammonia concentration in the colon because bacteria will metabolize the protein residues which enter the gut when carbohydrate levels are low. Ammonia, in turn, increases cell proliferation and alters DNA synthesis and has, therefore, been implicated in colon cancer.4 It is known that increased cell proliferation is associated with cancer in humans.8 Ammonia will not only be liberated from animal proteins, but from excessive intake of plant proteins as well. A high plant-protein intake is, however, usually associated with a high fibre intake and this would shorten the exposure time. This is particularly true in the case of whole foods with their high concentrations of fibre. High ammonia levels are not only a problem within the gut, but also effect the whole organism. As discussed in the chapter on proteins, the consumption of high levels of proteins will necessitate the deamination of amino acids in order to meet the body’s energy demands. This will require efficient detoxification of the produced ammonia, which in mammals is achieved via the urea cycle. As the amino acid arginine plays a principle role in this cycle, the higher levels of this amino acid in plant proteins than in animal proteins offers a possible protection against ammonia toxicity.
