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Effect of diet modification on human fecal mutagenic activity Bell, Penelope Anne


Dietary factors have been implicated in the etiology of colon cancer. The salient components of high-risk diets are thought to be high intakes of meat, especially beef, and fat, especially animal fat, and low intakes of fiber. Low-risk diets are thought to be high in fiber, and low in meat and animal fat. The present study examines the effects of short-term consumption of diets hypothesized to increase or decrease the risk for colon cancer on mutagenic activity of feces. Whether the fecal mutagens responsible for the mutagenic activity observed in the study are directly involved in the etiology of colon cancer is not known. However, most known mutagens are potentially carcinogenic, and fecal mutagenic activity may be an indicator of risk for colon cancer. Six healthy adult subjects consumed the following diets in sequence a baseline diet for one week, a low-risk lacto-ovo vegetarian, high fiber diet for two weeks, and a high-risk, high meat, low fiber diet for two weeks. Quantitative daily food intake records were kept, and daily bowel habits were recorded. Fecal samples were collected at the end of each diet period. Analyses were performed of the diets for food and nutrient intake, and of feces for percent dry weight and pH. Mutagenic activity of the fecal samples was assayed using the fluctuation test for mutagens. The subjects' habitual diets, although omnivorous, were found to closely resemble a low-risk diet pattern. Analysis of the vegetarian and high meat diets confirmed that the subjects had consumed foods which respectively represented the components of high-risk and low-risk diets. The overall fecal mutagenic activity obtained with samples on the high meat diet was higher than with the vegetarian or baseline diets using Salmonella typhimurium TA 98 and TA 100. The trend towards higher mutagenicity on the high meat diet over the vegetarian diet was consistent for all six subjects using TA 100, and for five of the six using TA 98. The vegetarian and baseline diets resulted in similar overall mutagenic activity. Analysis of the fecal sample parameters using the Kruskal-Wallis one-way analysis of variance showed no significant differences among fecal samples from the three diet periods with respect to wet weight, dry weight, percent dry weight, pH or number of daily bowel movements. However, a sign-test analysis showed a significant trend (p<0.05) towards fewer bowel movements on the high meat diet than on the vegetarian diet. There were significant differences among subjects for all of the fecal sample parameters (p<0.01 or p<0.001). Spearman rank correlations were significantly positive between mutagenic activities using bacterial strains Salmonella typhimurium TA 98 and TA 100 for the baseline diet (p<0.01) and the vegetarian diet (p<0.05). There were also significant positive correlations (p<0.001) between pH and fecal mutagenicity on the high meat' diet using tester strain TA 100, and between wet weight and dry weight. The results of this study indicate that the overall mutagenic activity of human feces can be increased over a period of two weeks by the consumption of a diet high in meat and low in fiber, which is considered to be a high-risk diet for colon cancer.

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