Ketogenic Diet for SIBO: Carb Restriction vs. Fat Malabsorption

In short: a ketogenic (keto) diet has not been studied in SIBO. Cutting carbohydrates reduces the food that gut bacteria ferment into gas, so it can ease symptoms. In a 2024 randomized trial in people with IBS, 71% responded to a low-carbohydrate diet, similar to the 76% who responded to a low-FODMAPFODMAPs Fermentable oligo-, di- and monosaccharides and polyols: short-chain carbohydrates that are poorly absorbed and quickly fermented by gut microbes. diet². Diets reduce symptoms but do not clear SIBO⁶. The downsides are a high fat intake, which some people with SIBO absorb poorly, too little fiber, and, in mouse experiments, loss of beneficial bifidobacteria³.

This guide covers what keto and low-carb diets do in the gut, what the research shows, and how to use carbohydrate restriction with SIBO without the main pitfalls.

Why cutting carbohydrates eases symptoms

Bacteria ferment carbohydrates into hydrogen, methane and other gases, which cause the bloating, pain and altered bowel habits of SIBO. SIBO diets work by reducing carbohydrates, so there is less food for the bacteria and less gas⁶. A keto diet takes this further, cutting carbohydrates so far (the 2009 study below used 20 g a day) that the body switches to burning fat and making ketones¹³.

SIBO diets are used to reduce symptoms, not to clear the overgrowth, which needs antibiotics, herbal antimicrobials or an elemental diet⁶.

What the research shows

The IBS trials did not test for SIBO. The 2009 study had no control group¹. The low-carbohydrate diet in the 2024 trial was fiber-optimized and high in protein and fat, not a strict keto diet².

Possible downsides with SIBO

Fat absorption

In SIBO, bacteria can break down the bile acids needed to absorb fat, which can lead to poor absorption of fat and fat-soluble vitamins⁷. A very high-fat diet may then cause loose, greasy stools. If this happens, a lower-fat, low-FODMAP approach may suit you better. Tell your doctor, because fat malabsorption can lead to vitamin deficiencies.

Bile-tolerant and sulfide-producing bacteria

In a 2014 study of 10 volunteers, five days of an animal-based diet increased bile-tolerant bacteria, including Bilophila wadsworthia, which turns sulfite into hydrogen sulfide⁴. Keto diets based heavily on meat and dairy fat may therefore not suit people with hydrogen sulfide SIBO. This has not been tested directly.

Fiber and constipation

Strict keto diets are often low in fiber. For people with methane overgrowth, which is linked to constipation, a 2025 nutrition review stresses the importance of adequate fiber to avoid making constipation worse⁵.

Fewer beneficial bacteria

In the 2020 study, a ketogenic diet changed the gut microbiome in ways that differed from a standard high-fat diet. In mice, ketone bodies directly inhibited the growth of bifidobacteria³, a group often considered beneficial. By contrast, a 2021 study found that a diet high in fermented foods increased gut microbial diversity⁸.

Using carbohydrate restriction safely

• Keep it short. Use carbohydrate restriction to manage symptoms during treatment, then broaden your diet. A 2025 review advises keeping SIBO diets as non-restrictive as possible to avoid nutritional deficiencies⁵.
• Prefer a structured diet. The low-FODMAP diet worked as well as a low-carbohydrate diet in the 2024 trial and has a built-in reintroduction phase².
• Watch fat tolerance. If high-fat meals cause greasy or loose stools, reduce fat.
• Keep some fiber, especially if you have methane overgrowth or constipation⁵.
• Do not combine extreme restriction with treatment without advice. Talk to your doctor or a dietitian, especially if you have diabetes, kidney disease or a history of eating disorders.

See our SIBO diet guide for an overview of SIBO diets.

Common questions

Can keto starve SIBO bacteria?

No. Reducing carbohydrates lowers gas production and symptoms, but it does not clear the overgrowth⁶.

Is keto or low-FODMAP better for SIBO?

Neither has been compared in SIBO. In IBS, a low-carbohydrate diet and a low-FODMAP diet worked about equally well². Low-FODMAP is less restrictive of carbohydrates overall and is designed to be broadened.

Should I do keto before a breath test?

No. A breath test only needs a short preparation diet the day before, low in fermentable foods. Follow the instructions from your test provider.