Intermittent fasting and constipation: why it happens and the fix
Eating fewer times a day can throw off your bathroom routine at first. Simple tricks to stay regular while you fast.
Part of the complete guide Intermittent fasting and health: side effects, precautions and special cases
What the science saysIntermittent Fasting and Constipation: The Fixes
Intermittent fasting can cause constipation indirectly: you eat less volume and less fiber, drink less water, and get fewer digestive cues across the day. It usually resolves by increasing water, fiber (vegetables, fruit, beans, seeds) and physical activity; black coffee and magnesium also help move things along.
- Dietary fiber increased stool frequency versus placebo (OR 1.19) in a meta-analysis of 5 trials (Yang 2012). [1]
- Magnesium oxide (0.5 g x 3/day for 4 weeks) improved constipation in 70.6% of people versus 25% on placebo (Mori 2019). [2]
- Black coffee, caffeinated or not, increased distal colon motility within 4 minutes in sensitive people, lasting at least 30 min (Brown 1990). [3]
Why can fasting back you up?
It isn't fasting itself, it's usually the knock-on effects: you eat less volume and less fiber, you drink less than you think, and with fewer meals there's less stimulus for your gut. It almost always clears up with small tweaks.
Hydration: cause #1
During a fast it's easy to forget to drink. Less water means drier stools, which means constipation. Drink plenty of water throughout your fast; unsweetened coffee and tea count too.
Get enough fiber in your window
With fewer meals, you have to make the fiber count in the ones you do eat: vegetables, whole fruit, beans, seeds, oats. If your window is nothing but protein and fat, your gut pays for it.
Other tricks that work
- Magnesium (citrate) at night helps things move.
- Movement: a walk wakes up your gut.
- A black coffee in the morning triggers the gastrocolic reflex.
- Don't hold it in when the urge shows up.
When to see a doctor
If the constipation is severe, painful, or drags on for weeks despite hydrating and eating fiber, talk to your doctor. Don't treat it as normal.
How Ayúname helps
Ayúname reminds you to hydrate during your fast, which is the single biggest factor in preventing constipation. A small detail with a big payoff.
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Frequently asked questions
Does intermittent fasting cause constipation?
What helps with constipation while fasting?
Scientific sources (4)
- Effect of dietary fiber on constipation: A meta analysis. World Journal of Gastroenterology, 2012.
- A Randomized Double-blind Placebo-controlled Trial on the Effect of Magnesium Oxide in Patients With Chronic Constipation. Journal of Neurogastroenterology and Motility, 2019.
- Effect of coffee on distal colon function.. Gut, 1990.
- Effects of regular physical activity on defecation pattern in middle-aged patients complaining of chronic constipation. Scandinavian Journal of Gastroenterology, 2005.