Two hundred grams per day of broccoli for 17 days resulted in 37% increase in the proportion of Bacteroidetes relative to Firmicutes, according to data presented at the Experimental Biology 2017 meeting in Chicago this week by scientists from the University of Illinois at Urbana-Champaign, ARS-USDA, and the National Cancer Institute.
The Firmicutes/Bacteroidetes ratio is reportedly a good biomarker for obesity, with data from a 2005 study by Jeffrey Gordon and his group at Washington University in St. Louis indicated that obese mice had lower levels of Bacteroidetes and higher levels of Firmicutes, compared with lean mice.
“These novel results reveal that broccoli consumption affects the diversity and composition of the GI microbiota of healthy adults,” they wrote in the FASEB Journal. “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.”
The potential health benefits of cruciferous vegetables, such as broccoli, cauliflower, and cabbage, are linked to the high levels of the plant chemicals glucosinolates. These are metabolized by the body into isothiocyanates (such as sulforaphane), which have been suggested to be powerful anti-cancer agents.
When eaten as a raw or lightly-cooked food, an enzyme called myrosinase in the broccoli help to break down the glucosinolates into two valuable compounds of intensive research interest – sulforaphane and erucin. The only sources we have for this enzyme is from the plant itself, or from our own microflora.
“It has been hypothesized that plasma sulforaphane observed in persons eating cooked broccoli may be related to glucoraphanin hydrolysis by microbial myrosinase,” explained the researchers in their study abstract. “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.”
The researchers recruited 18 healthy adults to participate in their controlled feeding, randomized, crossover study. The participants were randomly assigned to consume a control diet with 200 g of cooked broccoli or 20 grams of fresh daikon radish for 17 days. This was followed by 24 days “washout” period, before crossing over to the other group. The radish was used as a control because it is a source of plant myrosinase.
Results showed that broccoli consumption for 17 days significantly increased the proportion of Bacteroidetes relative to Firmicutes by 37% from baseline values. On the other hand, the control period was associated with a 5% reduction.
Additional analysis revealed that broccoli consumption was associated with a 6% increase in Bacteroides, while levels decreased by 2% in the control group. However, these results did not reach statistical significance, said the researchers.
“Additional study is ongoing to determine if phenotypic responses are related to archaea and body mass index,” they concluded.
Source: FASEB Journal
April 2017, Volume 31, Number 1, Supplement 965.18
“Broccoli Consumption Impacts the Human Gastrointestinal Microbiota”
Authors: J.L. Kaczmarek et al.