Broccoli Consumption Impacts the Human Gastrointestinal Microbiota
Authors: Kaczmarek Jennifer L , Charron Craig S , Novotny Janet A , Jeffery Elizabeth H , Seifried Harold E , Ross Sharon A , Swanson Kelly S , Holscher Hannah D 
Published: June 2021

Background

The human gastrointestinal (GI) microbiota is increasingly linked to health outcomes; however, our understanding of how specific foods alter the microbiota is limited. Cruciferous vegetables such as broccoli have been associated with cancer prevention as a result of their high levels of glucosinolates, especially glucoraphanin. The activation of glucoraphanin to its isothiocyanate form, sulforaphane, is dependent on the enzyme myrosinase. Myrosinase is naturally found in broccoli, but is degraded by cooking. It has been hypothesized that plasma sulforaphane observed in persons eating cooked broccoli may be related to glucoraphanin hydrolysis by microbial myrosinase. Myrosinase activity is greater in rodents who regularly consume cruciferous vegetables compared to those who do not, suggesting a priming effect on the microbiota. However, it remains to be discovered which members of the microbiota are responsible for this action in clinical populations.

Objective

We aimed to determine the impact of broccoli consumption on the GI microbiota of healthy adult men and women as a means to understand the role of microbes in glucosinolate hydrolysis.

Methods

A controlled feeding, randomized, crossover study consisting of two 17‐day treatment periods separated by a 24‐day washout was conducted in healthy adults (n=18). Participants were fed at weight maintenance, and received a Brassica‐free control diet or the same diet with 200 g of cooked broccoli and 20 g of fresh daikon radish (as a source of plant myrosinase) per day. Fecal samples were collected at baseline and at the end of each treatment period for microbial analysis. Following DNA isolation, bacterial, archaeal, and fungal barcoded amplicon pools were generated using a Fluidigm Access Array system prior to high‐throughput sequencing on an Illumina MiSeq. Data were analyzed using QIIME 1.8.0 and 1.9.1 and SAS 9.4.

Results

Beta diversity analysis based on 97% operational taxonomic unit composition and abundances indicated that bacterial communities were impacted by treatment (p=0.03). Broccoli consumption resulted in a significant change in the proportion of Bacteroidetes relative to Firmicutes, whereby participants consuming broccoli increased this ratio by 37% from baseline to end, compared to a 5% reduction during the control period (p=0.02). Bacteroides increased by 6% following broccoli consumption and decreased by 2% in the control group, but the difference between these two groups was not statistically significant (p=0.15).

Conclusion

These novel results reveal that broccoli consumption affects the diversity and composition of the GI microbiota of healthy adults. These data help fill the gap in knowledge related to the role of bacterial hydrolysis of phytonutrients. The increase in Bacteroides spp. is particularly relevant because Bacteroides thetaiotaomicron has been shown in vitro to utilize glucosinolates. Additional study is ongoing to determine if phenotypic responses are related to archaea and body mass index.

Support or Funding Information

Funding provided by the National Cancer Institute and the USDA.