Fermented foods are good everyday food for most people, but if you have SIBO – small intestinal bacterial overgrowth – you may find some of them make bloating and gas worse. The honest summary: there are no trials of fermented foods in SIBO, the evidence on probiotics is weak in both directions, and the decisions belong with the clinician treating you. This page explains what is known.
What SIBO Is
It’s normal to have bacteria in the small intestine, but too many can disrupt digestion, causing bloating, gas, abdominal pain, nausea and diarrhea or constipation. Risk factors include low stomach acid, certain medicines (including acid suppressants, antibiotics and narcotics), slow movement of the small intestine, structural problems after surgery or disease, and conditions such as diabetes, celiac disease and IBS. It is usually confirmed with a breath test measuring hydrogen and methane, and treated by addressing the overgrowth – typically with antibiotics – along with nutrition and the underlying cause (Cleveland Clinic). The American College of Gastroenterology has published a clinical guideline on diagnosing and treating it (Pimentel et al., 2020).
Because the symptoms overlap with IBS and other conditions, don’t diagnose SIBO yourself from how you react to sauerkraut or kefir – see a doctor.
Can Fermented Foods or Probiotics Make SIBO Worse?
Possibly for some people, but the evidence is thin:
- No trials of fermented foods in SIBO have been published that we could find; advice online is extrapolated from probiotic supplements and from what people report.
- Probiotic supplements: a 2024 systematic review found only low-quality evidence that probiotics help clear SIBO compared with placebo, from a few small, inconsistent trials (Fernando Niño et al., 2024); Cleveland Clinic describes the studies as inconclusive (Cleveland Clinic).
- A warning signal: a 2018 case series described patients with brain fog, gas and bloating, many taking probiotics, who had SIBO and D-lactic acidosis; their symptoms improved after stopping probiotics and taking antibiotics (Rao et al., 2018). A case series can’t show how common this is, but it is a reason not to self-treat bloating with ever-larger amounts of probiotics or ferments.
Why Some Ferments Are More Likely to Cause Symptoms
Much of the trouble in SIBO comes from fermentable carbohydrates feeding gas production, and some fermented foods carry more of them than others. Monash University, which developed the low-FODMAP diet, lists garlic and onion as high in fructans and milk and yogurt as high in lactose, while hard cheeses are low in lactose (Monash University). In practice that means:
- More likely to bother you: kimchi and other ferments made with garlic and onion; milk kefir and yogurt (lactose); sweet fermented drinks such as kombucha and water kefir, which keep some sugar and are fizzy.
- Usually gentler: aged hard cheeses; plain sauerkraut without garlic or onion, in small amounts; cooked ferments such as miso in soup.
Monash advises working with a dietitian before starting a low-FODMAP diet (Monash University), and that applies here too.
A Cautious Approach
- During diagnosis and treatment, follow your clinician’s advice on diet and probiotics.
- Afterwards, if you want fermented foods back, ask your doctor or dietitian how to reintroduce them. Trying one food at a time, in a small amount with a meal, and noting how you feel is the usual way to learn what you tolerate.
- Stop and get checked if symptoms return or new ones appear – weight loss, ongoing diarrhea or signs of poor absorption need medical attention, not a different ferment.
Related: how and when to eat sauerkraut, what kills probiotics, and our guide to fermented foods and IBS.
