It's the question that decides whether a probiotic can do anything at all, and the one most labels stay quiet about: do probiotics survive stomach acid? The short answer is that many don't — at least not in the numbers the front of the pack implies. Here's why that happens, and what to look for instead.
A note for transparency: in Great Britain, live cultures are not authorised to carry specific health claims, so nothing here should be read as a promise that a probiotic will treat or improve any condition. This is about the science of survival and how to read a label, not a health claim.
Why stomach acid is the problem
Your stomach is strongly acidic by design. One of its jobs is to neutralise the bacteria that arrive on everything you eat and drink. It can't tell the difference between unwanted bacteria and the friendly cultures in a probiotic — to your stomach, they're all just incoming microbes to be dealt with. So a probiotic capsule that simply dissolves in the stomach hands most of its live cultures straight into that acid bath, long before they reach the intestine where they'd actually settle.
What this means for CFU counts
This is why a big CFU number on its own can be misleading. CFU (colony-forming units) measures the live organisms at the point of manufacture. If a large share of those don't survive the stomach, the count that reaches your gut is far smaller than the headline figure. A more modest count that's protected to arrive intact can outperform a huge count that isn't. The number matters, but only alongside delivery. We unpack CFU and the other selection factors in our main guide to choosing the best probiotic for women in the UK.
What actually helps cultures survive
The key feature to look for is a delayed-release, acid-resistant capsule. Rather than dissolving in the stomach, this style of capsule is designed to stay closed through the acidic environment and open further down, in the intestine, where the cultures are meant to arrive. It's a simple bit of engineering that makes a real difference — and it's exactly why we use it in our Probiotic Capsules. Some products instead rely on strains that are naturally more acid-tolerant; the delayed-release capsule is the more direct, reliable approach.
A few practical pointers
- Look explicitly for the words delayed-release or acid-resistant on the capsule, not just a high CFU number.
- Some people take probiotics with or just before food, which can buffer stomach acid slightly — follow the label's guidance.
- A prebiotic (like inulin) doesn't affect survival but helps feed the cultures once they arrive — see our explainer on prebiotics versus probiotics.
- Consistency matters more than any single dose — live cultures are not a one-off fix.
The bottom line
If you take one thing from this: a probiotic is only as good as the cultures that actually reach your gut. The CFU count tells you what went in; the capsule technology tells you what's likely to arrive. Our 14-strain Probiotic Capsules pair 100 billion CFU with a delayed-release, acid-resistant capsule and prebiotic inulin, built around exactly this principle.
Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. If you are pregnant, breastfeeding, taking medication or managing a medical condition, speak to your GP or pharmacist before starting a new supplement. Signed, Dr. Miron, Founder of Pure Vitamins UK.
