The study, published in the Journal of Functional Foods, shows that when certain compounds in broccoli are broken down in the body, they create new metabolites that can have a potentially beneficial effect on specific receptors in the gut lining.
"There are a lot of reasons we want to explore helping with gastrointestinal health and one reason is if you have problems, like a leaky gut, and start to suffer inflammation, that may then lead to other conditions, like arthritis and heart disease," said Professor Gary Perdew of Penn State University. "Keeping your gut healthy and making sure you have good barrier functions so you're not getting this leaky effect would be really big."
The mouse data from the new study shows that broccoli consumption alters the host microbiome and improves intestinal resistance to chemical challenge – “which suggests there is a therapeutic effect on the maintenance of intestinal homeostasis.”
Good intestinal barrier function means that the gastrointestinal tract is helping protect the intestines from toxins and harmful microorganisms, while allowing nutrients to pass into the system, he said.
According to Perdew, the key to the process may be a receptor in the gut called aryl hydrocarbon receptor (AHR), which helps the body regulate its reaction to certain environmental contaminants and toxins.
The new data suggests that broccoli – along with other cruciferous vegetables like Brussels sprouts and cabbage – contain compounds known as indole glucosinolates, which breaks down into other compounds, including indolocarbazole (ICZ) in the stomach.
It is ICZ that then has been shown to bind to AHR – activating the receptor in the intestinal lining, and so aiding a raft of processes including barrier functions and maintaining a microbial balance in gut flora.
Local versus systemic activation
While the AHR has long been identified as potentially providing benefits for certain immune and digestive functions in the gut, Perdew noted that approaches that hyper-activate the receptor can cause toxicity.
However, using broccoli to activate the receptor locally in the gut rather than throughout the body on a systemic basis might help avoid some of these problems, he said.
"Dioxin, for example, activates this receptor, and if you hyper-activate it with dioxin, it will cause toxicity," he noted. "What we were interested in is: Could you locally activate the receptor naturally at a level that would cause only modest AHR activation in the gut, but not cause systemic activation, which could possibly lead to negative effects?"
According to the team, this approach could help prevent a variety of diseases, such as various cancers and Crohn's Disease, which is caused by inflammation in the lining of the gut.
Mouse data – human implications?
Perdew and his team used two genetic lines of mice in the study to focus on AHR. One line had a low ability to bind ICZ to AHR, while the other line had a high ability to bind ICZ to AHR. They added 15 percent broccoli to the diets of both groups of mice.
After adding a substance that causes digestive problems, the researchers said that the mice with a higher ability to bind ICZ to the AHR were protected from a chemical that induced digestive problems, but the mice with the lower affinity suffered.
For humans, the amounts of broccoli used in the study are equivalent to eating about 3.5 cups of broccoli each day, Perdew said.
"Now, three and a half cups is a lot, but it's not a huge amount, really," he commented. "We used a cultivar -- or variety -- with about half the amount of this chemical in it, and there are cultivars with twice as much.”
As such, the team concluded that the selection and breeding of cultivars which have higher levels of the compound could be seen as beneficial.
“Also, Brussels sprouts have three times as much, which would mean a cup of Brussels sprouts could get us to the same level,” Perdew suggested.
Furthermore, efforts to find the best way for people who have certain digestive conditions like colitis to consume such amounts easily – when they are often warned against too much roughage in the diet – would be a valuable step, they said.
Source: Journal of Functional Foods
Volume 37, October 2017, Pages 685-698, doi: 10.1016/j.jff.2017.08.038
“Dietary broccoli impacts microbial community structure and attenuates chemically induced colitis in mice in an Ah receptor dependent manner”
Authors: Troy D.Hubbard, et al