Spinach leaves in a wooden bowl on a table

Gut bacteria and leafy greens



Spinach leaves in a wooden bowl on a table


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 everyday. 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 Food Guide but in it’s last iteration, in 2007, it made a come back.


Go for dark green vegetables such as broccoli, romaine lettuce and spinach [sorry kale]

Go for orange vegetables such as carrots, sweet potatoes and winter squash


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Whether or not it stays with the anticipated food guide revision scheduled to come out in 2019 is unknown. Dark green vegetables are a great source of folate, lutein, zeaxanthin and beta carotene that support our hearts, brains and eyes. They’re also an important source of the much needed magnesium too.


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Leafy greens hold the key to 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 in leafy green vegetables. This discovery may help to explain how ‘good’ bacteria protect your gut and promote health.


The results of the study show that leafy greens are essential for feeding your microbiota. When your intestinal residents have access to their preferred food, they reproduce! Their children have children, who have 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 the gut. 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 load up on some sulfoquinovose – SQ for short


Sulfoquinovose…..say it with me.


Nothing more than a type of carbohydrate, SQ is a sugar found in leafy greens. Each year, green leafy vegetables around the world produce this unique sugar in enormous amounts; more than enough to feed all of our gut bacteria that are craving it.


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


Like prebiotic fibers (also technically sugars) in other foods like artichokes, SQ increases the number of good bacteria in your gut. What’s a little different about SQ is that it has sulfur – the ‘S’ in the diagram below. SQ is the only sugar molecule that has sulfur. The bacteria in your gut LOVE sulfur and why not? Sulfur is a critical mineral which 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 too.



Sulfoquinovose sugar molecule found in leafy vegetables



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.”


FUN FACT: when we ‘eat’ leafy greens full of sulfur, our bacteria digest and absorb it too. They use it to make proteins for themselves and then, when bacteria die, they ‘release’ [via pooping] the sulfur back into the environment where it is used by other organisms to use, grow, live and reproduce. The circle of life 🙂


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 refer to this particular strain.


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. This barrier is what crowds out other bad bacteria. Don’t be alarmed if you ever hear how green veggies are good because they boost levels of E coli.


Getting more SQ is easy…..eat more greens

  • Kale
  • Spinach
  • Collard greens
  • Mustard greens
  • Romain lettuce
  • Arugula
  • Dandelion greens
  • Beet greens
  • Dark green leaf lettuce


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 under neath 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.


A white bowl full of fresh kale leaves on a table


Study details:

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, and mental health.  Follow me on Facebook, Instagram and Twitter.

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