How Cruciferous Veggies May Protect the Gut
We investigated how different vegetables, such as kale, broccoli, cauliflower, Brussels sprouts, and cabbage, affect inflammation in the gut.
We know that eating our greens is essential for a well-balanced diet. Vegetables provide vital benefits, including fiber, vitamins, minerals, and antioxidant phytochemicals—all crucial components of a health-supporting diet.
As a botanist, I have long been fascinated by cruciferous vegetables of the species Brassica oleracea, which belongs to the Brassicaceae (mustard/cabbage) family. The diversity of form and flavor within this single species is remarkable! Through the selection of different traits—such as size, color, and shape—this species has given rise to varieties like broccoli, kale, red cabbage, green cabbage, Brussels sprouts, cauliflower, savoy cabbage, and more. It's incredible to consider how these unique forms evolved through centuries of selection and cultivation.
As a scientist, I am fortunate to have the tools to explore questions that pique my curiosity, such as:
How beneficial are cruciferous vegetables for our health?
To ferment or not to ferment? Which preparation method yields the greatest health benefits? For example, is sauerkraut or kimchi (fermented cabbage) better for us than raw or boiled cabbage?
Lyles JT, Luo L, Liu K, Jones DP, Jones RM, Quave CL. Cruciferous vegetables (Brassica oleracea) confer cytoprotective effects in Drosophila intestines. Gut Microbes. 2021 Jan-Dec;13(1):1-6. doi: 10.1080/19490976.2021.1921926. PMID: 33966605; PMCID: PMC8115444.
To begin to explore these questions, I collaborated with gut microbiome expert Dr. Rheinallt Jones to investigate the chemical diversity and gut-protective effects of various B. oleracea varieties. You can read the full findings in our open-access paper, but here, I’ll break down some of our key discoveries.
Study Overview
Our study explored the health benefits of Brassica oleracea varieties and their potential to modulate the Nrf2 signaling pathway, a key cellular defense mechanism against oxidative and electrophilic stress. Indoles, compounds enriched in Brassica species, have been shown to enhance healthspan across various organisms by improving stress resilience and physical function.
Indoles, which are enriched in Brassica spp., extend the healthspan of diverse phyla by modulating sensitivity to stressors, extending reproductive span, and increasing motility in the aged.
The Nrf2 pathway plays a crucial role in maintaining gastrointestinal health by orchestrating antioxidant responses, mitigating damage from colitis, drug-induced injuries, and development of cancer. Using fruit flies (Drosophila melanogaster) as a model, we investigated how indole-rich B. oleracea varieties influence mucosal barrier integrity and reduce damage from pathogens, stressors, and immune responses, offering insights into their potential therapeutic applications for gut health.
Study Methods
We purchased organic produce from a local market and also used an outlier species (a wild Brassica relative from the Mediterranean) to create plant extracts for this study. We first diced and dried the plant material, then extracted it in 80% ethanol in water. We also lacto-fermented kale in a brine solution prior to extracting it to investigate how natural fermentation by microbes found on the plant changes the chemistry of the final product. Next, we examined the chemical makeup of the extracts using mass spectrometry, focusing on the presence of different types of indoles. Lastly, we fed the extracts to fruit flies before and after treatment with a chemical that damages the gut lining of the fly intestines.
Cytoprotective Effects of Cruciferous Vegetables
Our major findings were that:
Indole compounds were present in all of the cruciferous vegetables, but the chemical makeup of each variety differed, as did the fermented versus non-fermented kale.
The Nrf2 signaling pathway is activated in flies fed indole or cruciferous vegetables.
Flies that consumed extracts from broccoli or Brussels sprouts showed better protection against oxidative damage, demonstrated by higher survival rates following consumption of the poison, paraquat. Extracts from other vegetables didn’t offer the same level of protection, suggesting that the health benefits vary among different varieties of Brassica oleracea.
Flies fed cruciferous vegetable extracts for three days prior to a poison challenge with paraquat showed greater protective against leaky gut than vehicle, with broccoli showing the greatest protection.
(a) PCA Scores plot generated from chemical data showing lacto-fermented kale, broccolini, broccoli, and B. macrocarpa as chemically distinct from other Brassica spp. (b) Indole or B. oleracea extracts induce Nrf2 signaling in the Drosophila intestine. Detection of green fluorescence under the transcriptional control of a Nrf2-responsive element in third instar Drosophila larvae fed either indole (20 mM), or 10 mg/mL extracts of Brussels sprouts or broccoli extract for 4 hours. Note activation of Nrf2 responsive GFP following ingestion or indole, Brussels sprouts, or broccoli. (c) The B. oleracea varieties extracts confer potent cytoprotective effects in Drosophila intestine in response to an oxidative challenge. Graphs show the relative survival of Drosophila fed the indicated B. oleracea varieties extracts in response to paraquat challenge. Note the significantly enhanced survival of flies fed extracts of broccoli or Brussels sprouts and dinosaur kale or lacto-fermented kale. . (d) Extracts of B. oleracea varieties protect against a leaky-gut phenotype. The Drosophila were fed B. oleracea extracts for 3 days, then were subjected to a paraquat solution, spiked with blue dye, which induces a leaky gut phenotype. Flies that have a leaky gut at 72 hours are identified by exhibiting a visible blue color throughout their hemocoel within the body cavity.
One limitation of the study is that we only tried lacto-fermenting kale. In future work, we’d love to examine how other fermented cruciferous vegetables compare in cytoprotective effects against oxidative damage and leaky gut.
The Takeaway
While flies certainly aren’t the same as humans, they provide an excellent model system for exploring the pathways through which certain foods can activate gut-protective signaling mechanisms, such as Nrf2.
This early study suggests that consuming cruciferous vegetables—especially broccoli—may offer some protection for gut health. More research is needed, but in the meantime, I’ll keep enjoying these greens!
Yours in health, Dr. Quave
Cassandra L. Quave, Ph.D. is a Guggenheim Fellow, CNN Champion for Change, Fellow of the National Academy of Inventors, recipient of The National Academies Award for Excellence in Science Communication, and award-winning author of The Plant Hunter. Her day job is as professor and herbarium curator at Emory University School of Medicine, where she leads a group of research scientists studying medicinal plants to find new life-saving drugs from nature. She hosts the Foodie Pharmacology podcast and writes the Nature’s Pharmacy newsletter to share the science behind natural medicines. To support her effort, consider a paid or founding subscription to Nature’s Pharmacy or donation to her lab research.
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