Leafy greens on purple background

Gut Bacteria and Leafy Greens

Doug Cook, RDN

Written by: Doug Cook, RDN

Updated: November 30th, 2022

Leafy greens have long been promoted as a healthy food. Even Canada’s Food Guide used to have a directional statement about 50 years ago to include a dark green vegetable every day. I remember this advice as one of the nutritional nuggets my grandmother used to share with me; that and to have a dark orange vegetable daily too.

The message to have one serving of dark green vegetables was later removed from the previous Food Guides but in 2007, it made a comeback but then again, was removed in the 2019 version which is a missed opportunity in my opinion. It was then re-added in 2020, which you can view in Canada’s Food Guide here.

Dark green vegetables are a great source of folate, lutein and zeaxanthin and beta carotene that supports your heart, brain, and eyes. They’re also an important source of the much-needed magnesium too. But that’s not all, dark green leafy vegetables, in particular, have unique health-promoting properties.

Leafy greens and gut health

Important research has found how your gut bacteria, a.k.a. microbiota, love to feed on a unique sugar molecule [don’t panic ‘sugar’ is just another word for carbohydrate] found specifically in leafy green vegetables.

This discovery may help to explain how certain good bacteria protect your gut and promote health.

The results of the study show that leafy greens are essential for feeding your microbiota in a way that is different than how dietary fiber and prebiotic fiber does. When your intestinal residents have access to their preferred food, they reproduce! They have children, and their children have children, who have even more children and so on 🙂 .

As the number of good bacteria in your gut increases, they limit the ability of less desirable bacteria from reproducing and colonizing your digestive tract. It’s all an issue of real estate. The preferred bacteria crowd out the trouble makers. Let’s face it, there’s only so much space and it’s better for your gut and your health to have more of the good guys.

Time to get more sulfoquinovose

The unique sugar in question is, say it with me, sulfoquinovose (SQ for shore).

As mentioned, SQ is nothing more than a type of carbohydrate found in leafy greens.

Each year, green leafy vegetables around the world produce this sugar in enormous amounts; more than enough to feed all the gut bacteria of the entire human race that are craving it.


SQ  is produced at the colossal rate of 10,000,000,000 tons (that is 10 gigatons) per annum and is degraded by bacteria as a source of carbon and sulfur.

Like prebiotic fibers in other foods such artichokes, SQ increases the number of good bacteria in your gut. What’s a little different about SQ is that it contains sulfur – the ‘S’ in the diagram below.

SQ is the only sugar molecule that has sulfur. Why does this matter? Because, the bacteria in your gut LOVE sulfur and why not? Sulfur is a critical mineral that is needed for building protein. You’re not the only one who makes protein; the trillions of bacteria that you have living in, on and around you do as well.

Dr Goddard-Borger puts it plainly this way: the discovery could be exploited to cultivate the growth of ‘good’ gut bacteria. “Every time we eat leafy green vegetables we consume significant amounts of SQ sugars, which are used as an energy source by good gut bacteria.”

E coli to the rescue


Escherichia coli – E coli for short – are a common type of bacteria that normally live in the digestive tracts of animals and humans.

Most strains of E coli are harmless. If you have a negative reaction when you hear E coli, it’s because of the harmful strain “E coli o157 H7” that sometimes makes its way into the food supply. Outbreaks of harmful E coli-based food poisoning are referring to this particular strain, not the others.

But there are other strains of E coli that are protective. In the case of leafy green vegetables, SQ feeds the beneficial type of E coli which provides a protective barrier between you and other potentially pathogenic bacteria that reside in your gut.


When we ‘eat’ leafy greens full of sulfur, our bacteria digest and absorb it. They use it to make proteins for themselves and then, when the bacteria die and are released via pooping, the sulfur makes its way back into the environment where it is used by other organisms to use, grow, live and reproduce. The circle of life 🙂

Getting more SQ is easy peasy! 

Eat more leafy greens, every day.

Salads: use mixed dark green leafy vegetables as a base for your salads. Use a single vegetable or mix it up by using several different ones as a base for a variety of flavours and textures.

Sauteed: not the best for leaf lettuce but all the other greens do well being sauteed with onions, bell peppers, garlic, and oil. You can steam them slightly too in the pan by adding a little chicken or vegetable stock.

Stuffed: add any raw leafy green to your next submarine, sandwich or wrap. While not technically a sandwich or wrap, try adding some while leafy greens underneath your poached eggs or avocado toast.

Soup it: add leafy greens to stews and soups to ‘up’ the SQ content of your next winter lunch or dinner.

Blend and drink it: probably one of the easiest ways to sneak in some leafy greens. I add raw spinach to smoothies ALL-THE-TIME. Dark green or Romaine lettuce works well here too. Kale not so much unless you have a super fancy blender like a VitaMix which blends the coarse stocks really well.

Study Reference:

Gaetano Speciale, Yi Jin, Gideon J Davies, Spencer J Williams, Ethan D Goddard-Borger. YihQ is a sulfoquinovosidase that cleaves sulfoquinovosyl diacylglyceride sulfolipidsNature Chemical Biology, 2016; DOI: 10.1038/nchembio.2023

Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, mental health.  Follow him on FacebookInstagram and Twitter

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