Walk down the health aisle of any Boots or Holland & Barrett and you'll find a wall of jars promising to fix your gut. Probiotic capsules at £25 a month, "gut-healing" powders that taste of pond, bone broth in shelf-stable cartons, fermented this and prebiotic that. The marketing has gone into overdrive in the last few years, and it's leaning hard on a genuinely exciting bit of science — the idea that the trillions of bacteria living in your large intestine influence everything from digestion to mood to immune function. The trouble is that the science is young, much of it comes from mice or small short studies, and the gap between "this is plausible and interesting" and "buy this £40 powder" is being filled almost entirely by people who want your money.
So here's an honest sorting of it. Some of the gut-health advice floating around is solid, cheap, and genuinely worth doing. A fair chunk of it is expensive and does very little. And a surprising amount of the most heavily marketed stuff sits in a grey zone where it might help some people a bit, but nobody can promise you'll be one of them.
What's genuinely worth doing
The single most useful thing you can do for your microbiome costs nothing extra and isn't sold in a jar: eat a wider range of plants. The bacteria in your gut feed on the fibre and compounds in plant foods, and different bugs prefer different foods, so variety matters more than volume. The often-quoted target from the American Gut Project is around 30 different plant types a week — and before that number makes you panic, it counts herbs, spices, nuts, seeds, wholegrains, beans and tinned pulses, not just fresh veg. A tablespoon of mixed seeds on your porridge, a handful of frozen peas, a bit of rosemary, some tinned chickpeas in a curry: that's four already, and most of them cost pennies. The 30-a-week figure is a rough guide rather than a magic threshold, but the principle behind it — diversity feeds diversity — is one of the better-supported ideas in the whole field.
Fermented foods are the second thing worth your attention, and they're cheaper than the supplement version of the same idea. Live yoghurt, kefir, sauerkraut, kimchi and a few others contain live bacteria and the by-products of fermentation, and a 2021 Stanford study found that people eating more fermented foods over ten weeks showed more diverse gut bacteria and lower markers of inflammation. One study isn't the last word, and the effect sizes were modest, but it's real human data rather than a marketing claim. The catch is that "fermented" on a label doesn't always mean live — most supermarket sauerkraut sold in jars on a warm shelf has been pasteurised, which kills the bacteria you're after. Look in the chilled section for products that say "live" or "raw", or make your own, which is almost free and genuinely easy.
The third move is less about adding and more about subtracting: eat fewer ultra-processed foods. This is the part the supplement industry would rather you skipped, because there's nothing to sell you. The emulsifiers, sweeteners and additives that make packaged food shelf-stable and moreish appear, in early research, to be unhelpful for the gut lining and the bacteria that sit on it. The evidence here is genuinely mixed and a lot of it is observational, so I won't pretend it's settled. But swapping a daily shop-bought sandwich and crisps for something you assembled yourself is one of those changes that helps on about six fronts at once, and your microbiome is probably one of them.
A quick word on prebiotics versus probiotics
People muddle these constantly. Probiotics are the live bacteria themselves — the yoghurt cultures, the supplement strains. Prebiotics are the fibres that feed whatever bacteria you already have: onions, garlic, leeks, oats, slightly-underripe bananas, cold cooked potato and pasta. For most healthy women, feeding the bugs you've got with a varied, fibre-rich diet does more reliable good than trying to parachute in new ones from a capsule, and it costs the price of an onion.
What's mostly expensive marketing
Now the uncomfortable part. Most probiotic supplements aimed at generally healthy people are not worth the money. The strains in a £25 bottle are specific, the doses vary wildly, and the evidence that a random off-the-shelf probiotic improves gut health in someone without a diagnosed condition is thin. There are real exceptions — particular strains have decent evidence for specific situations, such as taking certain Lactobacillus or Saccharomyces boulardii strains during or after a course of antibiotics to reduce the risk of diarrhoea. But that's a targeted, short-term use with a named strain for a named reason. It is a world away from swallowing a daily capsule indefinitely because an advert implied your gut was somehow broken.
"Gut-healing" powders are the category I'd be most sceptical of. These tend to combine some genuinely fine ingredients — a bit of fibre, some prebiotic inulin, maybe a probiotic dusting — with a wall of impressive-sounding extras like L-glutamine, collagen and an alphabet of mushrooms, then charge £30 to £50 a month for the bundle. The fibre and the inulin might do something useful. You could get the same fibre from a bag of oats and a few onions for under a pound a week. The word "healing" is doing enormous unverified work on those labels, and unless you have a specific medical condition your gut lining does not need rescuing.
Then there's the kefir question, which is more nuanced. Kefir is a genuinely good fermented food — but the trendy bottled brands at £3 to £4 for a small bottle are charging a heavy premium for something you can make at home almost endlessly from a set of grains and ordinary milk, or buy as plain own-brand live kefir from most big supermarkets for a fraction of the cost. The food is worth eating. The price tag on the fashionable version is the marketing.
Worth saying plainly: if you have persistent bloating, pain, blood, dramatic changes in bowel habits or unexplained weight loss, none of this applies to you and no powder will fix it. That's a GP conversation, not a supplement-aisle one.
The honest bottom line
Here's where I'll plant a flag, because the field is so full of hedging that someone ought to just make the call. Spend your money on food, not on capsules. A weekly shop with more plant variety, a few genuinely live fermented foods from the chilled section, and fewer ready-meals will do more for your gut than almost any supplement marketed to a healthy person — and it'll cost less, not more. Skip the gut-healing powders entirely unless a doctor has specifically suggested one. Treat probiotic supplements as a targeted tool for specific moments, like a course of antibiotics, rather than a daily insurance policy.
And keep a healthy suspicion of any product that talks about your gut as if it were damaged and waiting to be rescued. The microbiome research is genuinely fascinating and moving fast, and in five years we may know far more about which interventions help whom. Right now, though, the confident claims are running well ahead of the evidence — and the most expensive options on the shelf are usually the ones with the least behind them. Your gut, frankly, would be happier with the onion.