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a Incidence of colon cancer per 100,000. b Percentage of isolates. Source: From Ref. 40.

a Incidence of colon cancer per 100,000. b Percentage of isolates. Source: From Ref. 40.

importance of investigating population dynamics and not merely population levels. For more information on the influence of the intestinal microbiota and diet on the risk for colon cancer, see the chapter by Rafter and Rowland in this book.

At this time (mid-1970s), researchers became concerned with the inherent variation between the different populations and the possible impact this may have on interpretation of the data (e.g., geographical, and genetic differences between the study groups). Subsequent investigations concentrated on comparing dietary changes within cultural populations. Initial work included comparison of two generations of Japanese living in Los Angeles, one maintaining the traditional Japanese (low-risk) diet and the other having adopted a high-risk Western diet (41). Interestingly, no statistically significant differences were seen in the predominant genera of the fecal microbiota of the two groups. In addition, though significant differences in the prevalence of certain species were observed between the dietary groups, the average age of the two groups was also significantly different (Table 3). So commenced the era of longitudinal studies, using individual subjects as their own controls. One of the first such studies investigated the fecal microbiota of three North Americans over several months and different dietary regimens (42). Greater interindividual variation (between different subjects) in species composition was seen than intra-individual variation (between multiple samples from the same subject). Drasar and coworkers (36) monitored volunteers' fecal habits and composition over a six-week period (3 weeks on a conventional diet, followed by 3 weeks on a high-fiber diet). The only significant changes corresponded to stool weight and transit times. Hentges and colleagues (43) followed 10 subjects during baseline (1 month on a typical American diet; control), a meatless diet (1 month), a high-beef diet (1 month) and control diet again (1 month). Three stool samples were collected from each subject during the fourth week of each dietary period. Bacteroides spp. counts were significantly higher during the high-beef diet than the meatless diet (P<0.01). Similar statistically significant observations were, however, seen

Table 3 Summary of the Statistically Significant Differences Between Japanese Subjects Consuming Different Diets
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