Prebiotics: the best foods to feed your gut microbiome
Garlic, Jerusalem artichoke, oats… some foods directly nourish your good bacteria. Find out which ones and how to add them to your diet.
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What prebiotics actually are (and why they differ from probiotics)
Prebiotics and probiotics are frequently confused, yet the distinction matters. Probiotics are live micro-organisms (beneficial bacteria). Prebiotics, on the other hand, are dietary compounds — principally specific fibres — that your body cannot digest, but that your gut bacteria love to ferment.
According to the reference definition from ISAPP (2017, updated 2025), a prebiotic resists digestion in the stomach and small intestine, reaches the colon intact, and is selectively fermented by beneficial bacteria such as Bifidobacterium and Lactobacillus. In plain terms: you cannot digest them, but your microbes can.
The main types of prebiotics are:
- Inulin and fructo-oligosaccharides (FOS): found in garlic, onion, and Jerusalem artichoke
- Galacto-oligosaccharides (GOS): concentrated in legumes
- β-glucans: characteristic of oats
What happens in your colon when you eat prebiotics
The fermentation of prebiotics by your microbiome produces short-chain fatty acids (SCFAs): acetate, propionate, and butyrate. These molecules are far from inconsequential:
- They nourish the cells lining the colon (colonocytes), strengthening the gut barrier
- They lower colonic pH, which inhibits the proliferation of pathogenic bacteria
- They modulate inflammation via specific cellular receptors (GPR43/41)
- They contribute to blood sugar regulation: a meta-analysis published in Diabetes Care (2021) demonstrated a reduction in HbA1c of 0.3 to 0.5% in pre-diabetic individuals
A meta-analysis covering 25 clinical trials (So et al., 2022, Nutrients) confirms that a daily intake of 5 to 20 g of prebiotics increases Bifidobacterium abundance by 0.5 to 1 log CFU/g of stool — a measurable and clinically meaningful gain.
The foods richest in prebiotics
Below are the best-documented dietary sources, with approximate values per 100 g (USDA/EFSA 2023 data):
| Food | Main prebiotic | Estimated content |
|---|---|---|
| Chicory root | Inulin | 15–20 g |
| Jerusalem artichoke | Inulin | 12–18 g |
| Garlic | Inulin / FOS | 9–16 g |
| Onion | Inulin / FOS | 6–10 g |
| Artichoke | Inulin | 4–9 g |
| Legumes (lentils, chickpeas) | GOS, resistant fibres | 4–8 g |
| Asparagus | Inulin | 2–5 g |
| Oats (rolled) | β-glucans | 3–5 g |
| Unripe bananas | FOS | 0.5–1.5 g |
| Pistachios | Various fibres | 2–4 g |
Good to know: cooking partially reduces inulin content. Raw garlic and onion are therefore more prebiotic than cooked, though both still offer worthwhile benefits when prepared.
How much to eat, and how to start without discomfort
Current guidelines set total fibre intake at 25 g per day for women and 38 g for men (EFSA 2022; Health Canada 2023). For specific prebiotics, the ISAPP 2025 consensus places the clinically effective dose between 5 and 15 g per day of inulin or FOS.
The challenge: 77% of European adults do not reach the recommended 25 g of daily fibre (EFSA, 2023). This deficit has measurable consequences — a cohort study (Vandeputte et al., 2019, Gut) shows that an intake exceeding 25 g per day is associated with a 20% increase in microbial diversity.
To avoid bloating (a very real fermentation effect when first introducing these foods):
- Increase intake gradually: add 5 g of prebiotic fibre per week
- Drink more water alongside
- Keep intake to a maximum of 30 g per day initially (EFSA recommendation)
- If you have irritable bowel syndrome (IBS), take particular care: some prebiotics (notably FOS and GOS) are FODMAPs and may worsen symptoms in sensitive individuals. A personalised approach with a healthcare professional is recommended.
3 practical ideas for adding more prebiotics to your daily diet
Breakfast: a bowl of porridge with an underripe banana. You combine β-glucans and FOS right from the start of your day.
Lunch: a lentil salad with raw red onion and a garlic-based dressing. Rich in GOS, inulin, and FOS.
Dinner: steamed asparagus with a handful of pistachios as a starter. Simple, effective, and very much appreciated by your Bifidobacterium.
One general finding from a study published in Nature Medicine (2021) is worth bearing in mind: eating 30 different plant foods per week is associated with 25% greater microbial diversity. There is no need to consume large quantities of everything — variety matters as much as volume.
Key takeaways
Prebiotics are not exotic supplements: they are present in everyday foods such as garlic, oats, and lentils. Feeding your microbiome is, above all, a matter of regular plant diversity, introduced gradually to give your gut flora time to adapt. A straightforward investment, with benefits that extend well beyond digestion.