Influence of diets high and low in animal fat on bowel habit, gastrointestinal transit time, fecal microflora, bile acid, and fat excretion.

Abstract

A B S T R A C T Epidemiological observations and animal experiments suggest that large bowel cancer is related to several factors. Among them, high dietary intakes of animal fat, the presence in the colon of relatively high levels of bile acids, specific patterns of intestinal microflora, slow transit through the gut, and low stool weights. Under metabolic conditions we have observed the effect on these variables of diets containing 62 or 152 g/day of fat mainly of animal origin in six healthy young men over 4-wk periods. No change attributable to the diet was observed in the subjects' bowel habit, fecal weight, mean transit time through the gut, or in the excretion of dry matter. Total fecal bile acid excretion was significantly higher on the high fat diet (320±+120 mg/day) than on the low fat diet (139.7 +63 mg/day) t test = 7.78 P < 0.001 as also was the total fecal fatty acid excretion, 3.1+0.71 and 1.14±0.35 g/day, respectively t test = 11.4 P < 0.001). The fecal microflora including the nuclear dehydrogenating clostridia were unaltered by the dietary changes as was fecal /3-glucuronidase activity. Dietary changes which increase animal fat intake clearly influence fecal bile acid excretion in a way that would favor the development of large bowel cancer if current theories prove to be true. Dietary fat however has no effect on overall colonic function so other components of the diet must be responsible for the observed associations of bowel cancer with slow transit and reduced fecal bulk.

Colonic mucosal proliferation is related to serum deoxycholic acid levels

“…High risk diets contain high proportions of fat and meat and low proportions of fiber and lead to intestinal changes, such as a higher cholesterol uptake, a change to a higher pH, 37 a lower transit time, and the presence of larger numbers of bacteria 38 deconjugating and dehydroxylating bile acids. These factors result in a higher bile acid input into the gut, 39 and, hence, a higher turnover of primary to secondary bile acids in the colon. 40,41 Secondary bile acids may then stimulate colonic epithelial proliferation and, thus, promote tumor development.…”

Bile Acid Metabolism by Colonic Bacteria in Continuous Culture: Effects of Starch and pH

“…Epidemiological studies have es tablished an association of dietary fat and the incidence of colon cancer [4,5,22,23] and the correlation between fat intake and fecal BA excretion is well documented [9,10]. Patients with colorectal cancer or adenomatous polyps have higher fecal BA concentrations com pared to healthy controls [24], In animal ex periments, secondary BA induce hyperprolif eration of colonic mucosal cells, and increase the sensitivity of the animals to carcinogens [6,7,13,14].…”

Role of bile acids in colorectal carcinogenesis

“…Indeed, it has been found that dietary fat increases the output and faecal concentration of bile acids [6], Epidemiological evidence has shown that populations with a high incidence of colorectal cancer and consuming a high fat and animal protein diet, excrete about twice the amount of secondary bile acids [7]. The concentration of these bile acids is even more increased.…”