The effects of yogurt diet on the microbial community of the gastrointestinal tract

Background/Question/Methods

The human gastrointestinal (GI) tract is a complex microbial ecosystem with nearly 10¹² microbes. Many of these microbes benefit the host e.g. by protecting from pathogens or by assisting in nutrient uptake. Recent evidence suggests that yogurt is a probiotic product that may confer health benefits to the host. However, there have been few studies on the effects of yogurt consumption on the microbial community within the human GI tract. The objective of this study was to determine if there is a quantifiable change in the microbial community within the human GI tract associated with regular consumption of commercial yogurt. Viability of bacteria in commercial yogurt was determined using plate counts on Lactobacillus selective media. A commercial yogurt with the highest plate counts was chosen for further study. A dietary study was then conducted on three human subjects. Subjects did not consume yogurt for two weeks. Starting on day zero, 500 g of commercial yogurt was consumed each day for 15 days. Fecal samples where collected every five days starting at day zero. Each sampling day, DNA was extracted, subjected to PCR amplification, and terminal restriction fragment length polymorphism (tRFLP) analyses to determine bacterial community structure. 

Results/Conclusions

At day 0 of the yogurt trial, subject A showed the least amount of microbial diversity when compared to subjects B and C.  Results from the Nonmetric Multidimensional Scaling (NMDS) ordination of tRFLP taxa suggested that subject A’s 0 and 5 day samples were similar in community structure but, completely different than test subjects B and C. After ten days of yogurt trial, test subject A showed a major change in microbial community when compared to days 0 and 5. Subjects B and C showed a slight shift in microbial community after 5 days of yogurt consumption, whereas after 10 days the shift was larger in community structure. Both subjects B and C were much closer to each other in distance on the NMDs ordinate plot while subject A was more of an outlier. Data showed that after continuous consumption of yogurt there is a moderate shift in microbial community over time from day 0 to day 5, and a larger shift from day 5 to day 10. Data also showed that with continuous yogurt consumption an individual’s microbial diversity may increase over time.