Leafy green vegetables are well known for their exceptional nutrient content: They're loaded with key vitamins, minerals and phytochemicals thought to keep your heart, brain and eyes healthy as you age. Now, new research has uncovered yet another reason to eat your greens: they have an oft-overlooked sugar that is good for your gut.
It's not the same sweet stuff found in cookies, cake and chocolate, though. The unusual sugar in green vegetables – called sulfoquinovose or SQ for short – is essential for good gut bacteria to thrive. SQ is the only sugar that contains sulfur, a mineral vital for building proteins.
In other words, every time you eat a spinach salad (or kale chips) you're promoting the growth of so-called good bacteria and squeezing out the bad bacteria. That's a good thing, since shoring up protective gut bacteria is believed to promote digestive health, bolster the immune system and perhaps even guard against obesity.
Other foods that fuel the growth of protective bacteria, called prebiotics, include kefir, artichokes, asparagus, bananas, chicory, dandelion root, garlic, jicama, leeks, onions, barley, rye and wheat.
The study, published on Feb. 15 in the journal Nature Chemical Biology, discovered how gut bacteria extract the SQ sugar from leafy greens in order to fuel their growth. It turns out that bacteria use a previously unknown enzyme, called YihQ, to absorb and break down SQ, releasing its growth-promoting sulfur.
The researchers, from Melbourne and Britain, say their findings could pave the way for the development of new types of antibiotics. For instance, the newly identified enzyme could be used to help deliver drugs to kill harmful gut bacteria while leaving the good gut bacteria untouched.
There are other reasons to eat leafy green vegetables beyond digestive health. A diet rich in leafy greens is associated with a lower risk of heart disease, stroke, hip fracture and certain cancers. And it's thought to guard against cataract, macular degeneration and glaucoma.
Eating at least one serving per day (1 cup of salad greens or one-half cup of cooked greens) has also been linked to better brain function and slower cognitive decline. Vitamin K, folate, lutein and beta-carotene in leafy greens are thought to be connected to improved brain function.
Include at least one serving of leafy greens in your diet every day. Eat them both raw and cooked. But don't stop at spinach. Other nutrient-packed greens include arugula, beet greens, collard greens, dandelion greens, kale, leaf lettuce, mustard greens, rapini, Romaine lettuce and Swiss chard.
Most research suggests that salad greens, in particular, are beneficial for brain health. But, that doesn't mean you should always eat your leafy greens raw. You will get more minerals – calcium, magnesium, iron – from cooked greens than raw. Heating vegetables releases some of the minerals that are bound to natural compounds called oxalates. Cooking also increases the amount of antioxidants available for your body to absorb.
Whether raw or cooked, enjoy leafy greens with a little fat to help your body extract more fat-soluble nutrients and phytochemicals, including vitamin K, lutein and beta-carotene. Eat raw greens with an oil-based salad dressing or dip; add a teaspoon of flax oil or tablespoon of nut butter to your green smoothie; sauté leafy greens in olive oil, canola oil, grapeseed oil or coconut oil.
Seven easy ways to eat more greens
Include a variety of leafy greens in your diet – aim for at least one serving (one cup raw, one–half cup cooked) each day.
Try these seven simple ways to make that easier.
Snack on it
Make your own kale chips by tearing washed kale into bite-size pieces (4 cups) and toss with a tablespoon of olive oil and a dash of salt and pepper. Spread on a baking sheet; bake at 350 F for 15 minutes, or until crispy.
Assemble your favourite sandwich ingredients, taco fillings or stir-fry on trimmed collard or Swiss chard leaves and fold the leaf as you would a burrito. If you prefer, you can soften the leaves before filling by blanching in a saucepan of boiling water for 30 to 60 seconds.
Purée a handful of raw or frozen, precooked greens into a fruit or green smoothie. Or, make a green juice by blending Romaine lettuce, kale, cucumber, green apple and ginger.
Stir chopped or baby greens into tomato-based pasta sauces during the last few minutes of cooking; cook until the greens are wilted or tender. My favourite additions to pasta include chopped rapini and baby spinach.
Add chopped kale, Swiss chard, collards, mustard or beet greens to sautéed garlic and red chili pepper flakes and sauté until tender.
Drizzle with lemon juice and a sprinkle of Parmesan cheese or roasted sesame oil for an Asian-inspired side dish.
If Romaine or leaf lettuce is your go-to salad green, mix it up. Toss in baby arugula, dandelion greens, chopped kale or chopped beet greens. Pass on fat-free salad dressings; many nutrients and phytochemicals in leafy greens are best absorbed in the presence of a little fat. Top cooked pizza with raw salad greens such as baby arugula or spinach.
Fortify homemade or store-bought soups with chopped or baby greens (ditto for chili and stir-fries). If using baby greens, add them at the end of cooking.
Leslie Beck, a registered dietitian, is based at the Medisys clinic in Toronto.