Prebiotics: What They Are and the Best Foods to Feed Your Gut

A healthy gut microbiome doesn’t just depend on which bacteria are present. It also depends on what you feed them.

When we talk about gut health, probiotics tend to get most of the attention.

But there is another important part of the conversation: prebiotics.

Prebiotics are certain types of carbohydrates and fibers that your body does not fully digest. Instead, they travel through the digestive tract and become fuel for beneficial bacteria living in the colon.

An easy way to remember the difference:

Probiotics are beneficial microorganisms.
Prebiotics are the foods that help nourish them.

And fortunately, you don't necessarily need another supplement to get them.

Many everyday foods naturally contain prebiotic fibers and other compounds that help support a healthy, diverse gut microbiome.

Why Do Prebiotics Matter?

We have trillions of microorganisms living in and around our digestive tract.

These microorganisms interact with digestion, metabolism, immune function, the intestinal lining, and even communication between the gut and brain.

When beneficial gut bacteria ferment certain prebiotic fibers, they produce compounds called short-chain fatty acids, including butyrate.

These compounds can help support:

• A healthy intestinal lining

• Regular bowel movements

• Microbial diversity

• Healthy immune function

• Normal inflammatory balance

• Blood sugar and metabolic health

• Mineral absorption

• Gut-brain communication

In other words, supporting the microbiome isn't only about adding beneficial bacteria.

We also need to feed the bacteria that are already there.

Where Do You Find Prebiotics?

Prebiotic compounds are naturally found in many plant foods.

Some particularly good sources include:

Vegetables: garlic, onions, leeks, asparagus, artichokes, Jerusalem artichokes, dandelion greens, jicama, scallions, fennel, cabbage, Brussels sprouts, broccoli and cauliflower.

Fruits: slightly green bananas, apples, pears, berries, kiwi, peaches, nectarines, plums, pomegranate and avocado.

Beans and legumes: lentils, chickpeas, black beans, kidney beans, navy beans, pinto beans, cannellini beans, peas and edamame.

Whole grains: oats, barley, rye, wheat bran, whole wheat, buckwheat and quinoa.

Nuts and seeds: flaxseed, chia seeds, almonds, pistachios and walnuts.

The goal isn't to eat every food on the list.

It's to gradually include different sources throughout the week.

Resistant Starch: Another Way to Feed Your Gut

One interesting type of prebiotic carbohydrate is resistant starch.

As the name suggests, resistant starch "resists" digestion in the small intestine. This allows more of it to reach the colon, where gut bacteria can ferment it.

Sources include:

• Green bananas and green banana flour

• Plantains

• Beans and lentils

• Oats

• Cooked and cooled potatoes

• Cooked and cooled rice

• Cooked and cooled pasta

Here's an easy kitchen strategy:

Cook your potatoes or rice, refrigerate them, and enjoy them later.

The cooling process increases some of the resistant starch. They can be eaten cold or reheated.

Prebiotics Aren't Just About Fiber

There is another group of plant compounds worth mentioning: polyphenols.

Polyphenols aren't traditionally classified as dietary fiber, but they interact closely with the gut microbiome. Gut bacteria help metabolize polyphenols, while polyphenols may influence which microorganisms thrive in the digestive tract.

You'll find them in foods such as:

• Berries

• Pomegranate

• Apples

• Grapes

• Cherries and plums

• Cocoa

• Green and black tea

• Coffee

• Extra virgin olive oil

• Herbs and spices

• Colorful vegetables

• Nuts and seeds

This is one reason we often encourage patients to think beyond simply getting "enough fiber."

The variety of plant foods you eat matters, too.

Different foods provide different fibers and plant compounds, which feed different members of the gut microbial community.

Do You Need a Prebiotic Supplement?

Not necessarily.

Prebiotic supplements can be helpful in certain situations, but food is a wonderful place to start.

Instead of worrying about a specific number of grams of inulin, FOS, GOS or resistant starch, think about what you can add to your meals.

You might:

• Add onions, garlic or leeks when cooking.

• Put berries on oatmeal or yogurt.

• Add ground flax or chia to breakfast.

• Include beans or lentils a few times each week.

• Choose oats or other intact whole grains.

• Add another vegetable to dinner.

• Try cooked and cooled potatoes or rice.

• Rotate the fruits and vegetables you buy each week.

• Use herbs and spices generously.

Small changes can add up to considerably more microbial diversity over time.

But What If Prebiotic Foods Make You Bloated?

This is important.

More prebiotics aren't always better, especially at first.

Because gut bacteria ferment prebiotic fibers, increasing them can naturally increase gas production.

For someone with a relatively healthy digestive system, this may simply require a gradual adjustment period.

For someone experiencing IBS, SIBO, constipation, diarrhea, significant bloating or other digestive symptoms, certain prebiotic foods may be poorly tolerated.

That doesn't automatically mean those foods are unhealthy or that you should avoid prebiotics forever.

It may mean we need to consider:

• Which fibers you're eating

• How much you're eating

• How quickly you increased them

• Your bowel regularity

• Your individual microbiome

• Whether an underlying digestive issue needs attention

Sometimes supporting gut health means adding more fiber.

Other times, we need to improve digestive function and tolerance before asking the microbiome to handle more fermentation.

Start Low, Go Slow

If you're working on increasing prebiotic foods, don't feel like you need to overhaul your diet overnight.

Start with one or two changes.

Give your digestive system time to adjust.

Drink adequate water, support regular bowel movements, and notice how your body responds.

Most importantly, focus on variety rather than perfection.

Vegetables, fruits, legumes, whole grains, nuts, seeds, herbs and spices all bring something a little different to the microbiome.

Over time, those everyday choices help create a more nourishing environment for the microorganisms that share your digestive tract with you.

Rachel Oppitz, ND

This information is for educational purposes and is not intended to diagnose, treat, cure or prevent disease or replace individualized medical care.