Prebiotics: What Are They and How Can You Get Them From Food?

Your gut health is the cornerstone of your immune system, mood balance, hormonal health, and overall wellbeing. But are you feeding your beneficial gut bacteria the right way? In this article, you'll learn what prebiotics are, how they differ from probiotics, and which foods naturally support your gut flora.

What Are Prebiotics?

Prebiotics are types of carbohydrates—mainly fibres and certain plant compounds—that our bodies cannot digest. Instead, they travel to the colon intact, where they serve as fuel for beneficial gut bacteria. When microbes ferment these compounds, they produce short‑chain fatty acids (SCFAs) such as butyrate, acetate, and propionate. These SCFAs strengthen the gut lining, lower inflammation, balance blood sugar, and support overall metabolic and immune health.

Not all fibres are prebiotic, but all prebiotics are a form of fibre (or fibre‑like). The most researched prebiotics include inulin and fructooligosaccharides (FOS), but science now recognises a wider spectrum of compounds with prebiotic effects—including resistant starch and certain polyphenols.

Beyond Inulin & FOS: Fibre, Resistant Starch, and Polyphenols

While inulin and FOS are classic examples, they are not the whole story.

• Dietary Fibre: Whole grains, legumes, fruits, and vegetables provide diverse fibres that different microbes thrive on. A varied, fibre‑rich diet is key for microbial diversity.

• Resistant Starch: This starch resists digestion in the small intestine and reaches the colon intact, where it ferments and produces beneficial SCFAs like butyrate. Sources include cooked and cooled potatoes or rice, legumes, oats, and unripe (green) bananas.

• Polyphenols: These plant compounds (from berries, cocoa, coffee, green tea, grapes, etc.) largely bypass absorption in the small intestine and are metabolised by gut bacteria. Their breakdown products encourage beneficial microbes, reduce inflammation, and support gut barrier integrity.

Dr. Will Bulsiewicz’s Perspective

Gastroenterologist Dr. Will Bulsiewicz, author of Fiber Fueled and a doctor whose work I have read and followed for years, emphasises that gut health is built on diversity of plant foods rather than focusing on one or two superfoods. He uses the acronym F‑GOALS to illustrate key categories:

• Fruit & Fermented foods

• Greens & Grains

• Omega‑3‑rich foods

• Aromatics (onions, garlic, herbs, spices)

• Legumes

• Seaweed, Sulforaphane‑rich crucifers (broccoli, cauliflower, kale, cabbage) and Mushrooms

This framework highlights that prebiotics come not only from classic fibres like inulin but also from resistant starches, polyphenols, omega‑3‑rich plants, and a colourful diversity of fruits and vegetables.

Health Benefits of Prebiotics

Research shows that a steady intake of prebiotic‑rich foods can:

• Increase beneficial bacteria like Bifidobacteria and Lactobacilli

• Support gut lining integrity

• Reduce systemic inflammation

• Help regulate bowel movements

• Improve mineral absorption (e.g. calcium, magnesium)

• Potentially support mood and cognitive health through the gut‑brain axis

Best Natural Sources of Prebiotics

Here are some of the best foods to naturally support your gut microbiome:

• Garlic, onions, leeks (rich in inulin and FOS)

• Asparagus, Jerusalem artichokes, dandelion greens

• Bananas (especially green or slightly underripe)

• Cooked and cooled potatoes, rice, and legumes (resistant starch)

• Oats, barley, rye (beta‑glucans and resistant starch)

• Apples, berries, grapes (fibre and polyphenols)

• Cocoa, green tea, coffee (polyphenols)

• Legumes: beans, lentils, chickpeas (fibre, resistant starch)

• Nuts and seeds, especially flax, chia, and hemp (fibre + polyphenols)

Tips for Adding Prebiotics Into Your Diet

• Start slowly: Increasing fibre and prebiotic foods too quickly can cause gas and bloating. Introduce them gradually.

• Aim for diversity: Different microbes prefer different fuels. Eating 30+ different plant foods per week is a good framework.

• Combine with probiotics: Fermented foods like sauerkraut, kefir, or kimchi introduce beneficial bacteria that thrive when paired with prebiotics.

• Consider timing: Cook, cool, and reheat potatoes, rice, or pasta to increase their resistant starch content.

Prebiotics vs Probiotics vs Postbiotics

• Probiotics are live bacteria found in fermented foods like yoghurt, kefir, and sauerkraut.

• Prebiotics are fibres that nourish those bacteria, helping them flourish in your gut.

• Postbiotics are a byproduct of a probiotics in your gut when they eat what fertilises and grows them (prebiotics)

For optimal gut health, it’s essential to consume on a daily basis both prebiotics and probiotics.

Takeaway

Prebiotics are not just about inulin or a single food—they encompass a wide variety of fibres, resistant starches, and polyphenols that nourish your microbiome. As Dr. Bulsiewicz emphasises, it’s the diversity of plant foods that matters most. By regularly including foods like garlic, legumes, oats, green bananas, berries, and even cocoa or green tea, you’re feeding your gut microbes the fuel they need to keep you healthy.

you are looking for personalised nutritional counselling to improve your daily diet, please don't hesitate to reach out to me info@katrinpeo.com.