Short-Term Reciprocal Diet Exchanges Between African Americans and Rural Africans Impacts the Microbiota Composition and Activity

BACKGROUND AND AIM: Native Africans (NA) have a very low incidence and mortality of sporadic colorectal cancer (CRC) compared to populations in Western countries. Remarkable, of all racial and ethnic groups, African Americans (AA) have among the highest rates of CRC in the USA. Since consumption of animal meat and fat is associated with CRC risk, we hypothesize that differences between the Western (high fat and protein) and African diets (low fat and protein, high starch and fibers) cause the differences of composition and activity of the microbiota which contribute to the differential CRC risk. METHODS: In this study, 20 African and 15 African Americans healthy middle aged volunteers were subjected to reciprocal diet exchange under strict controlled in-house conditions over two weeks. African subjects were fed an energy distribution of 51% FAT, 27% PRO, 20% CHO, 3 g fiber/1000 kcals; and African-American subjects were fed an energy distribution of 17% FAT, 15% PRO, 68% CHO, 21 g fiber/1000 kcals. Fresh fecal samples were collected and frozen immediately before and after diet exchange. Fecal bacterial DNA was isolated and subsequently used for microbiota profiling using the Human Intestinal Tract Chip (HITChip), a 16S rRNA-based phylogenetic microarray covering over 1000 of the currently known bacterial species from the intestine. RESULTS: Microbiota profiling demonstrated significant differences between NA and AA at baseline (p,0.001). Notably, differences in microbiota composition were observed in the Bacteroidetes phylum with Prevotella being the dominant genus in NA and Bacteroides in AA. Although the microbiota composition changed significantly in AA and NA after the short dietary exchange (p,0.001), the differences in composition caused by the diet were relatively subtle compared to the baseline differences between the AA and NA groups. While the microbiota changes were not uniform in the AA group, the Parabacteroides distasonis group (from 4.7% to 7.5%, p=0.047) Dorea formicigenerans group (from 0.7% to 2.0%, p=0.047), and the Clostridium orbiscindens group (from 0.3% to 1.4%, p=0.017) were the most dominant groups that significantly increased after the diet exchange. The diet-induced changes in the microbiota are accompanied with changes in colonic SCFA, notably butyrate, which increased from 7.48±2.07 to 13.96±3.01 (p=0.046) in AA consuming the African diet and decreased from 19.96±4.72 to 4.92±1.66 (p=0.038) in NA consuming the Western diet. CONCLUSION: This study well illustrates that chronic dietary consumption is probably responsible for the differences in enterotype patterns observed between populations, while acute dietary change can modify microbial activity to increase the production of metabolites that may reduce risk of colonic carcinogenesis