Earlier studies have reported that faecal pH is more alkaline in patients with colonic cancer, indicating a reduction in colonic carbohydrate fermentation to organic acids. The pH of faeces from 11 pre and 14 postoperative, selected colonic cancer patients without intestinal obstruction, major loss of appetite or weight, not treated with antibiotics, and without signs of dissemination or recurrence of the cancer, did not differ, however, from faecal pH in 17 patients with previous colonic adenomas removed by polypectomy and faecal pH in 17 age matched (mean 61 years) healthy controls (mean (SE) 7.03 (0.10), 7.15 (0.11), 7.20 (0.12), 7.11 (0.12) respectively; p = 0.82). Faecal pH in 20 younger (mean 32 years) healthy controls tended to be lower (6.89 (0.07) compared with the older age matched control group (p < 0.06). Faecal concentrations of D-, L- or total D+L-lactate did not differ between the patients with present or previous colonic cancer, adenomas, and the healthy controls (D+L-lactate mean (SE) 3.2 (0.5), 3.1 (0.3), 3.5 (0.7), 4.1 (1.0) mmol/l respectively; p = 0.72), and the production pattern of lactate from different carbohydrates (glucose and dietary fibre) in 16.6% faecal homogenates was similar in all the three groups of patients and the healthy controls. Faecal pH was changed within days by modifications of the diet. An enteral diet free of fibre, starch, and lactose increased faecal pH within three days, whereas pH decreased when the colonic load of carbohydrates was increased by lactulose. Therefore, the reported alkaline faecal pH in patients with colonic cancer may reflect short term reduction in dietary intake and colonic fermentation secondary to the presence of the cancer, especially in patients with advanced disease, rather than long term differences in the precancer dietary habits.
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