Prebiotics vs Probiotics: Differences, Foods and Benefits

01Difference

What is the difference?

• Probiotics: live bacteria or yeasts, such as Lactobacillus, Bifidobacterium and Saccharomyces boulardii, that provide a benefit when taken in enough quantity.
• Prebiotics: non-digestible fibres and compounds that selectively feed beneficial microbes already in your gut.
• Synbiotics: products combining probiotics and prebiotics.
• Postbiotics: inactivated microbes or their components that may have health effects.
• Fermented foods may or may not contain live probiotic microbes, depending on processing.

02Probiotic foods

Foods with probiotics

• Yoghurt with “live” or “active” cultures.
• Kefir, a fermented milk drink.
• Unpasteurised sauerkraut and kimchi (pasteurised versions do not contain live bacteria).
• Miso and tempeh.
• Some cheeses, such as aged gouda and cheddar, may contain live bacteria.
• See our guide to fermented foods for gut health.

03Prebiotic foods

Foods with prebiotics

• Onions, garlic, leeks and spring onions.
• Asparagus and Jerusalem artichokes.
• Slightly green bananas.
• Oats and barley.
• Legumes such as lentils, chickpeas and beans.
• Chicory root and foods with added inulin.
• Apples and flaxseed.

04Evidence

What the evidence shows

Probiotics have the strongest evidence for preventing antibiotic-associated diarrhoea, with certain strains such as Lactobacillus rhamnosus GG and Saccharomyces boulardii, and for shortening some infectious diarrhoea in children. Some strains may modestly improve IBS symptoms. Evidence for probiotics in general “gut health”, immunity, weight loss or mood in healthy people is weaker and inconsistent. Prebiotics increase beneficial bacteria such as bifidobacteria and may support bowel regularity, but health benefits beyond that are still being studied. A diet rich in varied plant fibres is the most reliable way to support a diverse gut microbiome; see gut healthy foods.

05Women

Probiotics and prebiotics for women

Probiotics are often marketed for vaginal health. Some Lactobacillus strains have been studied for preventing recurrent bacterial vaginosis and thrush, with mixed results. They should not replace treatment for infections. Prebiotic fibre supports bowel regularity, which can help constipation in pregnancy and around menopause. Calcium and bone health benefit more from overall diet, vitamin D and exercise than from probiotics. Products marketed specifically to women are often similar to general products with different packaging.

06Supplements

Choosing a supplement

• Choose a product with strains studied for your specific purpose.
• Check the strain names (genus, species and strain code) and the number of colony-forming units at the end of shelf life.
• Follow storage instructions; some need refrigeration.
• Give it about four weeks; stop if there is no benefit.
• Higher numbers of strains or CFUs do not necessarily mean better.
• For antibiotic-associated diarrhoea, start with the antibiotic course and continue for a week afterwards.

07Side

Side effects and safety

Probiotics are safe for most healthy people. Initial bloating or wind is common and usually settles. Prebiotics, particularly inulin and FOS, can cause bloating, wind and discomfort, especially in people with IBS; increasing gradually helps. People with severely weakened immunity, central lines, critical illness or short bowel syndrome have a small risk of infection from probiotics and should only use them on medical advice. Low-FODMAP diets for IBS reduce some prebiotic fibres, so people with IBS should get tailored advice.

08Practical

Practical ways to support your gut

• Eat 30 different plant foods a week, including vegetables, fruit, whole grains, legumes, nuts and seeds.
• Include a portion of fermented food such as yoghurt or kefir most days if you enjoy them.
• Increase fibre gradually and drink enough water.
• Limit ultra-processed foods and alcohol.
• Use antibiotics only when needed.
• Exercise regularly and prioritise sleep.

09Cases

Three common situations

• Starting a course of antibiotics: a probiotic with Lactobacillus rhamnosus GG or Saccharomyces boulardii may reduce diarrhoea risk; ask a pharmacist.
• Bloating after taking an inulin supplement: reduce the dose or switch to food sources and increase gradually.
• IBS with mixed results from probiotics: try one product for four weeks and stop if there is no improvement; a dietitian can help.

10Microbiome

How the gut microbiome works

Your large intestine is home to trillions of bacteria and other microbes, collectively called the gut microbiome. They ferment fibre that you cannot digest, producing short-chain fatty acids such as butyrate that nourish the cells lining the colon and influence inflammation and metabolism. A diverse microbiome is generally linked with better health. Diet is one of the strongest influences: people who eat a wide variety of plant foods tend to have more diverse gut bacteria than those who eat few. Probiotic microbes from foods or supplements usually pass through rather than settle permanently, which is why regular intake is needed for any effect.

11Summary

Key points to remember

• Probiotics are beneficial live microbes; prebiotics feed them.
• Food sources come first: yoghurt, kefir, onions, garlic, oats, legumes.
• Supplement benefits depend on strain and condition.
• Vulnerable people should use probiotics only on medical advice.