SIBO testing and treatment in London

What SIBO is, and when testing makes sense

Small intestinal bacterial overgrowth means too many bacteria, or the wrong ones, living in the small intestine, which normally carries relatively few. They ferment food early, producing gas, and the result is typically bloating, wind, abdominal discomfort, and diarrhoea, constipation or both.

It is a real condition. It is also over-diagnosed in private practice and under-considered in general practice, and both of those cause harm. So I test where the history fits, not routinely. The patterns that make it more likely:

• Bloating that builds through the day, particularly within an hour or two of eating.
• A diagnosis of IBS that has not responded to the usual approaches.
• Long-term use of acid-suppressing medication such as omeprazole or lansoprazole.
• Previous abdominal surgery, or conditions that slow the gut, such as diabetes, hypothyroidism or some neurological conditions.
• Coeliac disease that has not settled on a gluten-free diet.
• Symptoms that improved on a course of antibiotics, then came back.

The breath test I use

The Genova Diagnostics 3-hour SIBO breath test. You drink a lactulose solution, a sugar the body cannot absorb, and collect eight breath samples over three hours at home. If bacteria are fermenting it in the small intestine, the gases they produce rise early and show up in your breath.

I use the three-hour version rather than the two-hour one because it picks up fermentation in people whose gut moves slowly, which is common in exactly the people most likely to have overgrowth, particularly those with constipation.

Hydrogen and methane mean different things

A rise in hydrogen suggests bacterial overgrowth and tends to go with bloating and looser stools. Raised methane is produced by a different group of organisms, archaea rather than bacteria, and tends to go with constipation. Current guidelines treat methane-dominant cases as a distinct condition, intestinal methanogen overgrowth, because they respond to different treatment. Measuring both is the point of the test.

How to prepare

The laboratory sends full instructions, and following them matters, because preparation affects the result more than most people expect. In outline: no antibiotics for about four weeks beforehand, a restricted diet the day before, an overnight fast, and no smoking or exercise during the test. Some medication needs pausing; I will tell you which before you start. Lactulose is not suitable if you have reacted to it before or follow a lactose- or galactose-restricted diet.

Being straight about its limits

Breath testing is the best non-invasive test available, and the 2017 North American Consensus set out how it should be done and read. It is still imperfect. Lactulose in particular can produce false positives when the gut moves quickly, because it reaches the large bowel, where fermentation is normal, sooner than expected. So I treat the result as one piece of evidence alongside your history, not as a diagnosis on its own.

Why I usually pair it with a stool analysis

The breath test looks at the small intestine. Many digestive problems also involve the large bowel, or digestion itself. So I often combine it with a comprehensive stool analysis, which looks at digestion and absorption, inflammation, the bacterial and fungal balance of the large bowel, and any organisms that should not be there. Together they cover the upper and lower gut.

There is a practical advantage too. Where the stool analysis grows an organism, the laboratory formally tests it against a panel of treatments, botanical as well as pharmaceutical, and reports which it is sensitive to. That means a choice between the two can rest on laboratory evidence from your own sample, not only on the published trials or on habit.

Before any of this, the common conditions that mimic SIBO need ruling out or have usually been ruled out already: coeliac disease, bile acid diarrhoea, pancreatic insufficiency and inflammatory bowel disease. The digestive health guide covers those in detail.

How treatment is chosen

There is no single SIBO treatment, and the choice is always a discussion with you. Both pharmaceutical and botanical antimicrobials are in the toolbox. Where a botanical option is suitable I will usually look at it first, and the final choice is the one that best fits your results and that you are most comfortable with. On the NHS, treatment is usually an antibiotic alone; here you have a choice, made with the evidence in front of you.

I also look at gut function more broadly, including intestinal permeability, often called 'leaky gut'. It is a real physiological measure, though one that is easily oversold, and I test or treat for it only where doing so would change what we do.

Recurrence after treatment is high across the published studies. That is usually a sign the reason for the overgrowth has not been dealt with, which is why the cause matters as much as the eradication.

When it is not a SIBO question

Some symptoms need NHS investigation first, whatever else is going on: bleeding from the bowel, unintended weight loss, difficulty swallowing, persistent vomiting, iron-deficiency anaemia, or a lasting change in bowel habit after the age of fifty. If any of those apply, I will make sure you are referred, and I will not order a breath test in place of it.

What it costs

The breath test is £231, including return of the samples to the laboratory. That is the laboratory’s price at the time of writing (October 2026); laboratories set and change their own prices, and I will confirm the current figure before ordering.

Testing is part of a consultation, not a standalone service. I see you first, so that the right tests are chosen, and then at a follow-up to go through the results and finalise a treatment plan that fits them and you. A functional medicine initial consultation is £880 for 120 minutes, and follow-ups are £440. A stool analysis, where it is needed, is priced separately, and I give you a written estimate before anything is ordered. Everything is on the fees page.

I see patients at The Maris Practice in Twickenham, in Richmond, and online across the UK. A first appointment is usually available within two to three weeks, and a free 15-minute discovery call is the best place to start.