Research
Adherence
Intermittent fasting is associated with minor, non-significant adverse events such as headache and constipation, comparable to control groups.
You may experience headaches or constipation when starting intermittent fasting, but these are common and manageable. They are not significantly worse than what you might experience on a standard diet, so they should not deter you from trying it.
ModerateSupportsMEDIUM confidence
Few studies report intermittent fasting-associated harms, but those that did reported prevalence of headache and constipation to be 5-13% and 6.5-8% respectively, which was not significantly different from control groups.
Why this rating
Based on limited reporting in included studies.
Source
Effect of Intermittent Fasting on Weight Loss and Risk Factors for Cardiovascular Disease and Diabetes: A Systematic Review
Ray Antonelli · Carolina Digital Repository (University of North Carolina at Chapel Hill) · 2019
DOI 10.17615/b4dd-gj08
systematic_review
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Intermittent fasting produces weight loss equivalent to daily caloric restriction, with no statistically significant difference in efficacy between the two methods.Moderate
- Intermittent fasting does not significantly improve cardiovascular risk factors (lipid profile, blood pressure) or diabetes markers (HbA1c, fasting glucose) compared to daily caloric restriction.Limited
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