Feed Your Gut

Prebiotics, probiotics and what all those billions of bugs actually want.

Once upon a time, yoghurt was simply yoghurt.

Now it's a delivery system for billions of friendly bacteria, promising to support everything from digestion to immunity and general wellbeing.

And that's before we've considered kefir, kombucha, prebiotic powders, probiotic capsules and the increasingly impressive claims appearing on supermarket shelves.

But what do all these terms actually mean?

And do we really need to buy expensive supplements to look after the microorganisms living in our digestive system?

The answer is rather more interesting — and less straightforward — than the advertising might suggest.

1. Your gut is home to a whole community

Our intestines contain trillions of microorganisms, collectively known as the gut microbiome.

These include bacteria, viruses, fungi and other microscopic organisms.

They interact with our digestive system, help process certain components of food and produce substances that can influence gut function.

One example is short-chain fatty acids, which are produced when some gut bacteria ferment dietary fibre.

These substances have important roles in the gut, including helping support the intestinal environment.

But microbiome science is complicated.

There isn't one universally ideal collection of bacteria.

And finding that people with a particular condition have different gut bacteria doesn't necessarily mean those bacteria caused the condition.

The microbiome matters. But that doesn't mean we can manipulate it as precisely as supplement advertising sometimes suggests.

2. Prebiotics — food for your microbes

Think of prebiotics as ingredients that certain helpful microorganisms can use.

More precisely, a prebiotic is a substance used selectively by microorganisms in a way that provides a health benefit.

Some types of dietary fibre are prebiotics, but not all fibre meets the scientific definition.

Examples include certain compounds found in:

  • Onions and garlic.

  • Leeks and asparagus.

  • Chicory root and Jerusalem artichokes.

  • Some bananas.

  • Certain pulses and wholegrains.

You don't need to eat all these foods.

And you certainly don't need to buy a special prebiotic powder.

A varied diet containing suitable fibre-rich plant foods is a sensible starting point.

One important consideration: some prebiotic-rich foods can increase gas and bloating, particularly for people with IBS.

Something can be beneficial in general and still be poorly tolerated by a particular individual.

3. Probiotics — adding live microorganisms

Probiotics are live microorganisms that, when given in adequate amounts, have been shown to provide a health benefit.

They're found in certain supplements and foods.

But here's the important bit.

Not every live microorganism is a proven probiotic.

And not every probiotic does the same thing.

Think of bacteria a little like different varieties of plants.

They may belong to the same broad family but have very different characteristics.

Research into one probiotic strain for one condition doesn't automatically apply to another strain or another condition.

That's why the words "contains billions of friendly bacteria" don't tell us very much on their own.

4. Does more bacteria mean better results?

Some supplements proudly advertise 10 billion, 20 billion or even 100 billion microorganisms.

It's tempting to assume that more must be better.

But the number alone doesn't establish whether a product works.

The particular strain, amount studied, intended purpose, product quality and ability of microorganisms to remain viable all matter.

A supplement containing enormous numbers of bacteria isn't automatically superior to one containing fewer.

And a mixture of multiple strains isn't necessarily better than a single well-studied strain.

The useful question isn't simply how many bacteria are in the product. It's whether that specific product has evidence for the benefit you're hoping to achieve.

5. Fermented foods — are they probiotics?

Fermentation is a process in which microorganisms transform ingredients.

Examples include yoghurt, kefir, sauerkraut, kimchi, miso, tempeh and kombucha.

Some fermented foods contain live microorganisms when consumed.

Others don't, particularly if they've been heated or processed after fermentation.

And even when live microorganisms are present, that doesn't automatically make the food a scientifically established probiotic.

Some fermented foods may be useful additions to a varied diet.

Live yoghurt, for example, can provide protein and calcium as well as live cultures.

But we should be careful about assuming that every fermented product has been proven to improve gut health.

Enjoy fermented foods if you like them. Just don't feel obliged to consume them as though they're medicine.

6. What does the research actually support?

There is evidence that certain probiotics may help with specific digestive problems.

For example, some people with IBS may experience symptom improvements, although results vary and the evidence is not consistent for every product.

Research also suggests that certain probiotics may reduce the risk of antibiotic-associated diarrhoea in some circumstances.

But there is much less convincing evidence for many broad claims about improving immunity, mood, skin, weight or overall health in otherwise healthy people.

The NHS notes that probiotic products sold as foods or supplements aren't assessed in the same way as medicines.

And the British Dietetic Association advises that healthy people are unlikely to need probiotic supplements routinely.

A promising research finding isn't the same as proof that every product on the supermarket shelf will help you.

7. What happens when you take antibiotics?

Antibiotics are important medicines used to treat certain bacterial infections.

But they can also affect bacteria that normally live in our gut.

This may temporarily change the microbiome and sometimes contribute to diarrhoea.

You may have heard that everybody should take probiotics after antibiotics to "restore their gut bacteria."

It's not that simple.

Some studies have found that particular probiotics can reduce antibiotic-associated diarrhoea, especially in certain higher-risk groups.

However, results differ between products and populations, and probiotics aren't routinely recommended by the NHS for everyone taking antibiotics.

Nor is there good evidence that taking an arbitrary probiotic supplement will reliably return your microbiome to its previous state.

For most people, the microbiome changes again over time, although recovery varies.

If you're prescribed antibiotics, take them as directed. Don't assume you need a probiotic supplement alongside them.

If diarrhoea is severe, persistent or accompanied by concerning symptoms, seek medical advice.

8. Can probiotics cause problems?

For many generally healthy people, probiotics are reasonably well tolerated.

Some people experience temporary bloating or gas.

However, people with significantly weakened immune systems, serious illnesses or certain other medical vulnerabilities may face greater risks from live-microorganism supplements.

They should seek medical advice before using them.

It's also worth considering the cost.

If a supplement is expensive and there isn't good evidence that it will help your particular situation, it may not represent good value.

More supplements don't necessarily mean better gut health.

9. What about microbiome testing?

Companies increasingly offer home stool tests promising to analyse your gut bacteria.

Some provide elaborate reports, scores and personalised food recommendations.

These can look very scientific.

But microbiomes vary naturally between people and over time.

At present, routine commercial testing generally cannot establish an individual's ideal microbiome or reliably tell them exactly which foods or supplements they need.

A low score on a commercial report isn't necessarily evidence of disease.

And changing your diet to chase a supposedly perfect bacterial profile may be unnecessary.

Interesting information isn't always clinically useful information.

10. What should you actually feed your gut?

For most people, a sensible food-first approach is the best place to begin.

Include a variety of fibre-containing plant foods that you enjoy and tolerate.

Try different vegetables, fruit, pulses, nuts, seeds and suitable wholegrains.

Increase fibre gradually if your current intake is low.

Include fermented foods if you enjoy them, without treating them as essential.

Avoid unnecessary restrictive diets.

And remember that bowel symptoms can have many causes beyond the microbiome.

If you have ongoing digestive difficulties, getting the correct diagnosis is more important than experimenting with expensive supplements.

A little self-reflection

  1. Do I understand the difference between prebiotics and probiotics?

  2. Am I eating a reasonable variety of fibre-rich plant foods?

  3. Which foods seem to agree with my digestion?

  4. Are there prebiotic-rich foods I could add gradually?

  5. Do I enjoy fermented foods, or am I eating them because I think I should?

  6. Have I bought probiotics based mainly on advertising claims?

  7. Do I know which strain and specific benefit a supplement is intended for?

  8. Am I assuming that more bacteria means a better product?

  9. Have I tried to treat persistent symptoms without seeking professional advice?

  10. Could a simpler, food-first approach meet my needs?

A practical exercise: Feed Your Gut — Without the Hype

QuestionMy answerWhich fibre-rich foods do I already eat regularly?Which other plant foods could I try?Are there foods that consistently trigger symptoms?Do I eat any fermented foods I enjoy?Am I taking a probiotic supplement? Why?What evidence supports that specific product for my intended use?What one practical food change could I make?

If you're considering a supplement, ask three additional questions:

What exactly am I hoping it will improve?

Has this particular strain or product been studied for that purpose?

Would it be more appropriate to discuss my symptoms with a GP or registered dietitian?

A final thought

Our gut microbiome is fascinating.

And research into how microorganisms interact with our bodies is developing rapidly.

But that doesn't mean we need to spend a fortune trying to perfect it.

For most people, eating a varied diet containing suitable fibre-rich foods is a much more sensible starting point than chasing the latest probiotic trend.

Specific probiotic products may have a role in certain circumstances.

But the details matter.

The strain.

The dose.

The condition.

And the quality of the evidence.

You don't need to buy billions of bacteria simply because the packaging tells you they're friendly.

Sometimes the most useful thing you can do for your gut is considerably less glamorous.

Eat your vegetables.

Something to think about, don't you think?

The science behind this sheet

FUSION FIT — MOVE WELL • EAT WELL • LIVE WELL

Disclaimer: This sheet provides general nutrition education, not individual medical or dietary treatment. People with weakened immune systems, serious medical conditions or persistent digestive symptoms should seek appropriate professional advice before taking probiotic supplements. Do not stop or alter prescribed antibiotics without medical advice.