Broccoli consumption affects the human gastrointestinal microbiota

Authors: KACZMAREK, JENNIFER - University Of Illinois; LIU, XIAOJI - University Of Illinois; Charron, Craig; Novotny, Janet; JEFFERY, ELIZABETH - University Of Illinois; SEIFRIED, HAROLD - National Cancer Institute (NCI, NIH); ROSS, SHARON - National Cancer Institute (NCI, NIH); MILLER, MICHAEL - University Of Illinois; SWANSON, KELLY - University Of Illinois; HOLSCHER, HANNAH - University Of Illinois

Submitted to: Journal of Nutritional Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2018
Publication Date: 1/1/2019
Citation: Kaczmarek, J.L., Liu, X., Charron, C.S., Novotny, J., Jeffery, E.H., Seifried, H.E., Ross, S.A., Miller, M.J., Swanson, K.S., Holscher, H.D. 2019. Broccoli consumption affects the human gastrointestinal microbiota. Journal of Nutritional Biochemistry. 63:27-34. https://doi.org/10.1016/j.jnutbio.2018.09.015.
DOI: https://doi.org/10.1016/j.jnutbio.2018.09.015

Interpretive Summary: The prevention of chronic diseases such as cancer has been a significant goal of nutrition research. Broccoli is a food which may reduce cancer risk. The cancer-protective properties of broccoli may be due to its high concentration of glucosinolates. Part of the biological activity of glucosinolates may derive from the action of microbiota on glucosinolates in the gastrointestinal (GI) tract. Conversely, microbiota may be affected by glucosinolates and other components of broccoli. Evolving research suggests that GI microbiota may play key roles in human health. In this study, we investigated how broccoli consumption affected the microbiota in humans. Eighteen subjects completed the study. For 16 days, subjects ate either a control diet with no broccoli (NB) or the same diet supplemented with cooked broccoli and raw daikon radish (DB) every day. Fecal samples were collected at the beginning and end of each diet period and were analyzed by DNA sequencing to characterize the GI microbiota. The data showed that microbial communities were affected by broccoli consumption. The ratio of Bacteroidetes to Firmicutes increased by 37% from baseline in response to broccoli intake. Bacteroidetes and Firmicutes are GI microbiota that have been associated with human health and may be related to leanness. Bacteroides vulgatus and Bacteroides thetaiotaomicron are specific types of Bacteroidetes that are known to metabolize glucosinolates, but were not affected by the broccoli treatment. This study indicates that daily broccoli consumption changes the populations of microbiota in the GI tract, which in turn may be important for human health. This information will be used by scientists and dieticians.

Technical Abstract: The human gastrointestinal microbiota is increasingly linked to health outcomes; however, our understanding of how specific foods alter the microbiota is limited. Cruciferous vegetables such as broccoli are a good source of dietary fiber and phytonutrients, including glucosinolates, which can be metabolized by gastrointestinal microbes. This study aimed to determine the impact of broccoli consumption on the gastrointestinal microbiota of healthy adults. A controlled feeding, randomized, crossover study consisting of two 18-day treatment periods separated by a 24-day washout was conducted in healthy adults (n=18). Participants were fed at weight maintenance with the intervention period diet including 200 g of cooked broccoli and 20 g of raw daikon radish per day. Fecal samples were collected at baseline and at the end of each treatment period for microbial analysis. Beta diversity analysis indicated that bacterial communities were impacted by treatment (P=.03). Broccoli consumption decreased the relative abundance of Firmicutes by 9% compared to control (P=.05), increased the relative abundance of Bacteroidetes by 10% compared to control (P=.03) and increased Bacteroides by 8% relative to control (P=.02). Furthermore, the effects were strongest among participants with body mass index <26 kg/m2, and within this group, there were associations between bacterial relative abundance and glucosinolate metabolites. Functional prediction revealed that broccoli consumption increased the pathways involved in the functions of the endocrine system (P=.05), transport and catabolism (P=.04), and energy metabolism (P=.01). These results reveal that broccoli consumption affects the composition and function of the human gastrointestinal microbiota.