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Feed Your Flora

Probiotics are living microorganisms that contribute to a healthy digestive tract.

Prebiotics are types of indigestible, fermentable fiber that encourage the growth of beneficial bacteria.

If you’ve been spooning down yogurt and embracing the tang of kombucha in the name of digestive well-being, you’re probably familiar with probiotics. The health-supporting powers of these live, active cultures found in fermented foods have been widely touted over the last few years. What you may not realize is that, like all living organisms, these healthy bacteria that populate your gut need to be nourished — and that their superfood is prebiotics.

“Think of prebiotics as the fertilizer that enables your gut garden to thrive,” says New York City–based integrative physician Frank Lipman, MD.

Prebiotics are types of indigestible fiber that are as critical to the health of your microbiome, and therefore the health of your body, as the microbes they feed. So, when tending to your gut, it’s important to give the beneficial bacteria residing there the prebiotics they need to flourish.

The Pros of Prebiotics

All prebiotics are fiber, but not all fiber is prebiotic. Prebiotic fiber resists digestion in the upper gastrointestinal tract, ferments in the colon (a.k.a. large intestine), and fuels the growth of probiotic microorganisms that are linked with optimal well-being. (For more on probiotics, see “Probiotics at Work.”)

Researchers are still working to identify the ways prebiotic fibers support human health. Many of the benefits attributed to a well-balanced microbiome are due to byproducts of fiber fermentation called short-chain fatty acids, or SCFAs, explains Jane Muir, PhD, head of translational nutritional science in the Department of Gastroenterology at Monash University in Melbourne, Australia.

As bacteria in the colon gobble up prebiotic fiber, they produce SCFAs, which, in turn, do many beneficial things:

  1. Balance gut pH. SCFAs reduce the pH of the intestinal lining, which makes the gut more acidic and less hospitable to pathogenic microorganisms.
  2. Boost nutrient absorption. This resulting change in pH may also increase the absorption of some nutrients. In one study of 100 adolescents, participants who took a daily prebiotic supplement absorbed 8.5 percent more calcium within eight weeks than those taking a placebo. Within a year, they had built more bone mass.
  3. Prevent leaky gut. SCFAs help strengthen the integrity of the intestinal wall, playing a key role in preventing leaky gut — a condition in which toxins penetrate the thin intestinal lining and cause a range of health problems, including allergies and autoimmune diseases.
  4. Curb cancer cells. One SCFA called butyrate has been found to quell the growth of colon-cancer cells; it also decreases inflammation in the gut. Another SCFA called acetate helps inhibit pathogenic organisms.
  5. Support satiety. Increased SCFAs in the gut contribute to better satiety and weight loss, as well as improved lipid and glucose metabolism.
  6. Reduce inflammation. SCFA production is also associated with decreased inflammation throughout the body — which improves cardiovascular and metabolic health, among other benefits.

While scientists do not completely understand all the mechanisms by which prebiotics work, research continues to link their consumption to a range of health improvements. Findings about the brain–gut connection, for instance, indicate that prebiotics may play a role in our emotional well-being.

When 45 healthy adults took a galactooligosaccharide prebiotic supplement every day for three weeks, their bodies produced lower levels of the stress hormone cortisol upon waking, according to an Oxford University study. And in an exercise within that study evaluating emotional response, those participants paid more attention to positive information than negative — a result similar to that found with certain antidepression medications. (For more on the mental-health benefits of prebiotics, see “Psychobiotics: Using Gut Bacteria to Treat Mental Illness.”)

Eat Your Prebiotics

Though you can buy supplements in the form of powders and capsules, experts say whole foods are the best (and arguably most enjoyable) way to get your prebiotics.

Plant-based foods that contain prebiotic fibers, including asparagus, cabbage, garlic, Jerusalem artichokes, and onions, are tops. (See “What’s in a Name?” further down to learn more about specific fibers.) Under-ripe bananas, as well as cashews, pistachios, lentils, and chickpeas, are great sources, too.

Unfortunately, many of us don’t eat enough of the foods that adequately nourish the health-promoting microbes in our guts.

“Our Western diet — which is lacking in vegetables, fruit, and fiber — is responsible for a decline in prebiotic intake,” says Natasha Haskey, MS, RD, who researches the gut microbiome at the University of British Columbia. (For even more reasons to eat your veggies, go to “How to Eat More Veggies.”)

The good news is that a little prebiotic food usually goes a long way, says Muir. “The amounts of prebiotics we need to have an impact on the gut microbiota are not high.”

Indeed, once you know what you’re looking for, it’s easy to include prebiotic-rich foods in your diet. Eat a handful of pistachios; add cooked or canned lentils to a soup (see “How to Cook Lentils” to learn about cooking lentils); or snack on a slice of watermelon.

(Also learn how probiotics and prebiotics support your muscle health at, “How Do Probiotics and Prebiotics Support Muscle Health?“)

Diversity Matters

Prebiotics clearly play a crucial role in gut health, but focusing on them in isolation misses the point: The gut microbiome is an ecosystem — and a healthy ecosystem is a diverse one.

Indeed, a diet rich in prebiotic fiber and probiotic foods helps support the production of health-promoting SCFAs.

You can even get your prebiotics and probiotics at the same time if you eat a fermented prebiotic-rich food — think pickled onions or pickled asparagus. Or you can combine a prebiotic-rich food with a probiotic-rich food: chickpeas with a dollop of yogurt, for instance, or raw onions sprinkled into miso soup. (For more serving ideas, see “Your Prebiotic Plate,” below.)

But don’t worry too much about whether a given meal meets both criteria. Instead, follow experts’ recommendation to eat both probiotic- and prebiotic-rich foods over the course of the day. And, because cooking can affect the prebiotic content of certain foods, it’s best to consume both raw and prepared veggies regularly.

“When it comes to the gut flora, diversity is the key to wellness for the entire body,” says Vincent Pedre, MD, FCMP, author of Happy Gut: The Cleansing Program to Help You Lose Weight, Gain Energy, and Eliminate Pain.

So go for lots of variety with a plant-heavy diet that includes plenty of pre- and probiotic foods. Your microbiome will thank you.

Your Prebiotic Plate

Try to eat more of these prebiotic-rich foods — and for extra credit, pair them with the suggested probiotics. Note that, generally, the less foods are cooked, the greater the prebiotic content.


Prebiotic fiber: Inulin and FOS.

Enjoy it: Raw or lightly steamed for the most prebiotics.

Probiotic pairing: Dip spears in a sauce made of plain kefir blended with a drizzle of olive oil, lemon zest, and a pinch of salt.

Unripe bananas

Prebiotic fiber: Resistant starch.

Enjoy it: Buy green and eat before fully ripened. Try sliced, mashed, or frozen and blended into “nice cream.”

Probiotic pairing: Whirl a frozen banana in a blender with plain, full-fat yogurt, a handful of greens, and a tablespoon of nut butter for a smoothie.

Buckwheat groats

Prebiotic fiber: Resistant starch.

Enjoy it: Allow cooked buckwheat to cool for the most prebiotics, then top a green salad with a scoop of these gluten-free pseudo-grains.

Probiotic pairing: Make buckwheat pancakes and serve alongside grilled tempeh “bacon” strips.


Prebiotic fiber: FOS.

Enjoy it: Toss raw cabbage with rice-wine vinegar and sesame oil for an Asian-inspired salad.

Probiotic pairing: Make your own sauerkraut for a pre- and probiotic treat.


Prebiotic fiber: Resistant starch.

Enjoy it: Soak and cook dried chickpeas to make hummus. (Canned chickpeas have lower levels of prebiotic fiber than dried.)

Probiotic pairing: Top hummus with naturally fermented pickles or other veggies.

Dandelion greens

Prebiotic fiber: Inulin.

Enjoy it: For the most prebiotics, eat these bitter greens raw; mix with milder salad greens like romaine and baby spinach.

Probiotic pairing: Top with goat cheese or a yogurt-based dressing.


Prebiotic fiber: FOS and GOS.

Enjoy it: Slice the bulb, which has more prebiotics than the fronds, and eat raw.

Probiotic pairing: Toss with plain yogurt and top with zaatar, a Middle Eastern spice mixture.


Prebiotic fiber: Inulin, GOS, and FOS.

Enjoy it: Eat raw for the most prebiotic power. Try sprinkling minced raw garlic into a warm soup as a spicy garnish.

Probiotic pairing: Chop crushed garlic and blend with plain yogurt, grated and drained cucumber, chopped dill, and lemon juice for an easy Greek tzatziki sauce.

Jerusalem artichokes

Prebiotic fiber: Inulin and FOS.

Enjoy it: Peel and slice thinly using a mandoline. Add raw to a salad, or toss with olive oil and roast at 400 degrees F until lightly browned.

Probiotic pairing: Try it with a kefir dressing: Blend plain kefir with olive oil, lemon zest, and salt.


Prebiotic fiber: Resistant starch.

Enjoy it: Add a scoop of cooked lentils to any salad for a prebiotic protein boost.

Probiotic pairing: In addition to lentils, top your salad with sauerkraut or other pickled vegetables.

Oats (rolled and steel-cut)

Prebiotic fiber: Resistant starch.

Enjoy it: Top cooked oats with a handful of wilted baby spinach, a sunny-side-up egg, and freshly ground pepper.

Probiotic pairing: Mix 1/3 cup each uncooked steel-cut oats, plain full-fat yogurt, and milk of choice in a Mason jar, along with 1 tablespoon chia seeds. Refrigerate overnight and serve in the morning with your favorite oatmeal toppings.


Prebiotic fiber: Inulin and FOS.

Enjoy it: Eat raw or lightly cooked for the greatest prebiotic effect. Try sprinkling raw into your favorite soup.

Probiotic pairing: Whisk miso paste with water and bring to a simmer for aromatic miso broth. Add onions and cook until just softened.


Prebiotic fiber: FOS and GOS.

Enjoy it: Eat a handful or sprinkle onto a salad for added crunch.

Probiotic pairing: Toss into a blender along with plain kefir, a handful of spinach, and a frozen banana for a prebiotic green smoothie.


Prebiotic fiber: Resistant starch.

Enjoy it: Boil and allow to cool. Toss with oil and vinegar and finely chopped veggies for a prebiotic side salad.

Probiotic pairing: Serve with sauerkraut.


Prebiotic fiber: FOS and inulin.

Enjoy it: Eat raw in a salad, or toss with olive oil and roast, then drizzle with balsamic vinegar.

Probiotic pairing: Mix raw, shredded radicchio with plain yogurt, lemon juice, and lemon zest for a side salad.


Prebiotic fiber: FOS.

Enjoy it: Cube and sprinkle with coarse sea salt for a simple snack.

Probiotic pairing: Top sliced watermelon with sprinkles of feta cheese, and drizzle with olive oil and balsamic vinegar.

What’s in a Name?

Eating more whole, plant-based foods is the healthiest way to get prebiotics into your diet. The following are some of the key prebiotic fibers found in food.

  • Fructans are chains of sugar molecules, found in a variety of vegetables and fruits, that store carbohydrates. Two types of prebiotic fructans are inulin and fructooligosaccharides (FOS).
  • Galactooligosaccharides (GOS) are chains of galactose sugars joined together with glucose at the ends. These occur naturally and are often also added to packaged foods.
  • Resistant starch refers to any dietary starch that is not digested in the small intestine but passes through to the colon, where it is fermented. (For more on this, see “Resistant Starch for a Healthy Gut.”)

Smart Supplementation

For those who don’t eat prebiotic-rich foods on a daily basis, a supplement is a good alternative, says integrative physician Frank Lipman, MD.

Pills and powders made with fructooligosaccharides (FOS) and inulin can help, though determining the appropriate dose can be challenging. “The right amount for each individual is different, because each of us has a slightly different makeup of gut bacteria creating the sum of our microbiome,” says Vincent Pedre, MD, FMCP.

Start with 1/4 teaspoon of a powdered supplement, gradually working your way up to 1 teaspoon, and eventually to 1 tablespoon. “The key is to start low and go slow,” he says.

“Increasing prebiotics can cause some gas and bloating at first as your gut flora is changing and adapting,” says Lipman. This is particularly true when increasing prebiotics through supplements, which provide higher doses than you’ll find in whole foods.

Jo Ann Hattner, MPH, RDN, author of Gut Insight, suggests consuming smaller amounts of prebiotic fiber more regularly. “Your tolerance to these fibers may be improved if taken throughout the day,” she says.

This originally appeared as “Feed Your Flora” in the April 2018 print issue of Experience Life.

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  1. what an excellent article! i have enjoyed and profited from your other articles about the microbiome. i also bought your 2 latest periodicals.

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