Determining the structural- and functional-level effects of diet-specific interventions on the gut microbiota of a diverse sample of Southern United States adults

Racial disparities in colorectal cancer (CRC) incidence persist for blacks and whites. Given the previous
work of our team documenting racial differences in the gut microbiota of blacks and whites and the evidence
supporting the interaction between diet and the gut microbiota as a risk factor for colorectal cancer, the study of
how various diets affect the structure and function of the gut microbiota across racial groups is warranted.
Previous research has shown that the gut microbiota can be rapidly altered by changes in diet. For example,
consumption of an extremely high fiber (>50 grams) diet has produced changes in the gut microbiota that are
believed to reduce cancer risk. The Dietary Approaches to Stop Hypertension (DASH) diet, rich in fruits,
vegetables, whole grains and low-fat dairy, is commonly recommended for heart health and has been shown to
lower blood pressure and produce weight loss. However, to our knowledge, the effect of the DASH diet on the
gut microbiota has not been studied. Because the DASH diet provides substantial fiber, we hypothesize that
consumption of the DASH diet will lead to improvements in the gut microbiota of non-Hispanic black and white
adults. In this proposal, we plan to investigate our hypothesis by recruiting a generally healthy sample of 112
black and white adults from Birmingham, AL to participate in a 28-day randomized, controlled feeding study.
Participants will be randomized to receive either the DASH diet or a standard American diet. All meals will be
provided by the study. Fecal samples will be collected at multiple time points before, during, and after the dietary
intervention and will be analyzed using PCR to amplify the V4 region of the 16S rRNA gene and to sequence
bases using the MiSeq platform. Sequenced data will then be analyzed using QIIME. We hypothesize that
participants receiving the DASH diet will have a greater increase in alpha diversity and greater changes in
abundances of CRC-associated microbes than participants receiving the standard American diet. We will also
evaluate functional-level markers including bile acid and short chain fatty acid (SCFA) production and
inflammatory markers. If our hypothesis is supported, we expect to see reduced production of secondary bile
acids (e.g., deoxycholic acid), greater SCFA production (e.g, butyrate), and reduction in gut and systemic
inflammation (e.g, calprotectin, IL-6) among participants receiving the DASH diet compared to the standard
American diet. Our findings will provide preliminary evidence for the DASH diet as an approach for cultivating
a healthier gut microbiota across racially diverse populations. These findings can impact clinical, translational,
and population-level approaches for modification of the gut microbiota to reduce risk of chronic diseases like
CRC.

Grant Number: 5R01CA253219-06
NIH Institute/Center: NIH
Principal Investigator: Tiffany Carson