Gut Microbiome Changes on a Ketogenic Diet
The gut microbiome responds rapidly to dietary shifts, and the ketogenic diet is no exception. By drastically reducing carbohydrates and increasing fat intake, this way of eating alters which bacterial species thrive in the digestive tract. Emerging research suggests these changes may influence everything from inflammation to blood sugar control.
How Carbohydrate Restriction Reshapes Gut Bacteria
When carbohydrate intake drops below 50 grams per day, the primary fuel source for many gut microbes disappears. Fibre-fermenting bacteria like Bifidobacterium, which thrive on resistant starch and soluble fibre, often decline. In their place, bacteria capable of metabolising fat and protein, such as Akkermansia muciniphila, become more abundant. A 2018 study in Cell Metabolism found that a carbohydrate-restricted diet rapidly reduced liver fat and altered microbial communities linked to metabolic health (Mardinoglu et al., 2018).
The Role of Short-Chain Fatty Acids
With fewer carbohydrates available for fermentation, production of butyrate—a short-chain fatty acid that nourishes gut lining cells—may decrease. However, some ketogenic dieters compensate by eating more fibrous vegetables like Brussels sprouts (£1.80 for 500g at Tesco) or supplementing with prebiotics. Interestingly, certain ketone bodies themselves, like beta-hydroxybutyrate, may have anti-inflammatory effects that indirectly support gut barrier function.
What This Means in Practice
UK supermarkets now stock keto-friendly fermented foods: sauerkraut (89p at Aldi), kimchi, and full-fat live yoghurt can help maintain microbial diversity. During the colder months, bone broth—rich in collagen—may support gut lining integrity. Those transitioning to keto often report temporary digestive changes as their microbiome adapts; the keto adaptation timeline typically spans 2-4 weeks.
Potential Benefits Beyond Weight Loss
While research is still evolving, some studies associate ketogenic diets with increased microbial diversity—a marker of gut health. A 2013 review in the European Journal of Clinical Nutrition noted improvements in inflammatory markers that may stem from microbial shifts (Paoli et al., 2013). These changes could partly explain why some people report reduced bloating and improved digestion after adopting keto.
Frequently Asked Questions
Will keto destroy my gut bacteria?
No. While some fibre-loving bacteria may decrease, others adapt or increase. Including diverse low-carb vegetables and fermented foods helps maintain balance.
Can I take probiotics on keto?
Yes. Look for strains like Lactobacillus and Bifidobacterium in sugar-free formulations. Live yoghurt and kefir are natural options.
Why does my digestion change when starting keto?
As microbial populations shift, some experience temporary constipation or diarrhoea. Increasing electrolytes and fluid intake usually helps during adaptation.
The Bottom Line
The ketogenic diet induces measurable changes in gut microbiome composition, favouring bacteria that metabolise fat and protein over those dependent on carbohydrates. While the long-term implications require more research, early evidence suggests these shifts may contribute to keto’s anti-inflammatory effects. If you’d rather not do the macro maths yourself, the Keto Dieting app does it for you on Google Play and the App Store.
References
- Mardinoglu A, Wu H, Bjornson E, et al. (2018). An Integrated Understanding of the Rapid Metabolic Benefits of a Carbohydrate-Restricted Diet on Hepatic Steatosis in Humans. Cell Metabolism. https://doi.org/10.1016/j.cmet.2018.01.005
- Paoli A, Rubini A, Volek JS, Grimaldi KA (2013). Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European Journal of Clinical Nutrition. https://doi.org/10.1038/ejcn.2013.116
