The Study
Adverse events and tolerability of ketogenic diets – a systematic literature analysis
This study looked at lots of other studies about keto diets and counted how often people got sick—like constipation or headaches. It doesn't prove the diet made them sick, just that lots of people on keto reported those problems. Think of it like a big survey of complaints, not a test of cause and effect.
Analysis score
Maximum 85 for a systematic review.
Where the score came from
When people eat very low-carb, high-fat diets like keto, their bodies change how they use energy — but this can cause side effects like tummy troubles and headaches.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 528 / 100
Quality score
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — nearly half of people experience mild but annoying side effects, especially stomach issues, and many quit because it’s hard to stick to.
- 243% of people on keto diets had at least one side effect; 24% got constipated; 40% had tummy problems; stricter diets caused more side effects; 17% quit the diet.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
BMC Nutrition
Year
2026
Authors
Carolin Schopf, Marc Assmann, Nadja Wolke, Marius Frenser, Thorsten Marquardt, Tobias Fischer
Related Content
Claims (5)
In studies of ketogenic diets, constipation, diarrhea, nausea, and vomiting were reported in 86% of the interventions and made up 40% of all side effects recorded, regardless of the participants' age or the specific version of the diet used.
Among people on ketogenic diets, about 17% stop following them, but this rate rises to 22% for stricter versions and 35% for people with serious illnesses like cancer, showing that sticking to these diets long-term is difficult for many.
Most research on ketogenic diets does not measure ketone levels in blood or urine, and less than half of these studies record this data, making it difficult to know if participants followed the diet properly or to understand why side effects occurred.
In people following ketogenic diets, 43% experienced at least one side effect, with 40% having gastrointestinal symptoms and 24% specifically experiencing constipation.
Diets that severely limit carbohydrates, such as the classic ketogenic diet and MCT-based diets, are linked to more frequent and more severe side effects than less restrictive low-carb diets like the modified Atkins diet or low glycemic index treatment.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.