| Considerable evidence indicates that diet and nutrition are crucial determinants for the modulation of colon cancer. In particular, consumption of oligosaccharides in conjunction with bifidobacteria has been associated with decreased risk of colon cancer. In contrast, animal fat and red meat are the most commonly suggested dietary enhancers of colon carcinogenesis. Intake of animal fat and red meat, such as beef, has been associated with an increased risk of colon cancer in some epidemiological studies, but other epidemiological studies found no association. Therefore the objective of the first experiment was to examine the effect of various oligosaccharides in combination with bifidobacteria administration on the risk of colon cancer in rats, using the number of colonic preneoplastic lesions (aberrant crypts, AC) and rate of cell proliferation as markers of colon cancer risk. Our results suggest that the combination of bifidobacteria and oligofructose consumption reduces the risk of colon cancer, suggestive of a synbiotic effect. The objective of the second experiment was to investigate the effect of beef protein and tallow on colon cancer development in rats, again using the number of AC and cell proliferation as markers. Additionally, apoptosis rate, and bile acid concentration including profile of individual bile acids were determined. Tallow decreased the risk of colon cancer compared to soybean oil as measured by a reduced number of AC. This correlated with a lesser bile acid concentration, and a greater apoptotic labeling index. Finally, in the third experiment, I determined the effect of diets containing beef protein, tallow and cocoa butter on colonic microbial enzyme activities in rats, specifically nitroreductase, β-glucuronidase and 7α-dehydroxylase, which are thought to play an important role in colon carcinogenesis. Different types of fat and protein affected the activity of microbial enzymes in a complex way, not necessarily correlated with the risk of colon cancer. Therefore, the relationship between microbial enzyme activity and aberrant crypt formation needs further investigation. |
