Can Fasting Improve Your Gut Health?
As fun as eating is, not eating would have to work really well for me to try it.
There are currently many diets, supplements, and lifestyle protocols advertising how they can help your digestive discomforts, and I don’t blame people for trying all of them. When you’ve been suffering from bloating, constipation, diarrhea, pain, GERD, or gas for a long time, it’s easy to get desperate. Insert fasting protocols.
There are many benefits to fasting, specifically in the spiritual health realm: greater connection with your internal feelings and cravings, the discipline of temporarily depriving yourself of something you enjoy, and an opportunity to remove the focus of your day from food. However, there are pitfalls to fasting, including sleep detriments, binge eating behaviors, and problems preserving muscle mass. People can also become very dogmatic around fasting. I’ve seen the comment thread on some private Facebook groups and subreddits, and some people make bold claims.
Today, we’re going to explore the use of fasting for gut health. Is it a trend? Can it be harmful to your gut? Or should it be part of everyone’s gut health strategy?
To Fast…
A 2006 study took 36 patients with IBS (Irritable Bowel Syndrome) who did not respond to traditional pharmacology and had them undergo ten days of “starvation” + 5 days of refeeding (1). Fasting therapy significantly improved abdominal pain & discomfort, diarrhea, abdominal distention (bloating), anxiety, and interference with life in general. This study makes me think, DUH! Not eating for ten days SHOULD rid you of bloating and abdominal pain if foods contribute to your IBS, as in many people. However, the improvement in anxiety is quite fascinating to me. That points to the power of the gut-brain connection in IBS.
Improve your gut health, improve your brain health, and vice versa.
Some of these improvements may have come from being in a calorie deficit for two weeks. It’s common for symptoms such as pain and bloating to go away from eating less than average. Sometimes, we just overeat. But what does this say about the power fasting can have, that ten days of starvation lead to improvements in anxiety? I’ll let you be the judge of that one.
The Most Studied Fasting Experiment
Every year, many people belonging to the Islamic faith take part in Ramadan. Ramadan includes fasting from food and liquid from sunrise to sunset for about 30 days. Because this event happens every year, it makes for a terrific science experiment, where lots of health data and information can be obtained pre- and post-Ramadan.
In those with Inflammatory Bowel Disease — Crohn’s or Ulcerative Colitis (UC) — participating in Ramadan fasting led to anxiety reductions and reductions in disease severity scores for those with UC (2).
Again, we see anxiety being a huge factor that changes due to fasting regimens.
Drastic changes occur to the microbiome during a fast, especially one to the extent of Ramadan, and we know certain bacteria produce molecules that contribute to feelings of calmness or anxiety. A 2021 study from The American Journal of Clinical Nutrition found that Ramadan was associated with an significant increase in microbial diversity in younger folks, but not in middle-aged folks (3).
Here’s the kicker: once Ramadan was over — and people started eating normally again — their microbiomes returned to its pre-fasting levels. This speaks to how malleable and adaptable our microbiome is.
If someone with dysbiosis of their microbiome undergoes fasting, such as Ramadan, they could see beneficial changes to their microbiome that leads to the production of more favorable compounds — neurotransmitters, short-chain fatty acids, etc.
Does that mean everyone with dysbiosis or IBD needs to fast? Absolutely not. Fasting is just another tool in the tool belt to support gut health. And as we’ll touch on shortly, a particular digestive symptom might be made worse with fasting.
Or Not to Fast…
In contrast to the previous evidence, another study found that those undergoing Ramadan were more likely to develop constipation, and the constipation symptoms got worse for those who fasted longer than two weeks (4). In line with that, another study in which obese people were undergoing eight weeks of alternate day fasting — alternating between a fast day where you eat 25% of your everyday calories and a “feeding” day where you eat whatever and as much as you want — constipation was the most prevalent adverse side effect (5).
The former two studies show that fasting may not be the best approach if you suffer from constipation. However, does that mean you should never fast if you have constipation? Again, absolutely not. If anything, it means you may have to be a bit more mindful of your hydration status, daily activity level, and what you’re eating when you are eating.
What this Gut-Health Physician has Noticed
From my experience, my “digestive flares” tend to veer more toward the constipation end, and I still do time-restricted feeding (TRF) daily, with occasional longer fasts. I haven’t noticed the fasting per se flares constipation, but rather a new environment — moving to a new state or on vacation — can sometimes flare it.
I’ve seen and worked with many people who report huge improvements in their digestive symptoms, mental clarity, and overall energy when they do some kind of TRF daily — 14–20 hours of fasting, 10–4 hour eating window. These people also tend to be generally in better health, so is fasting driving 100% of those benefits? Quite a possibility. Or maybe it’s the “placebo effect” of thinking they’re doing the right thing by time-restricted feeding.
Returning to my leading title, should you be fasting for your gut health? It depends. If you’re seeking more specific guidance on fasting, IBS, IBD, or general digestive health, I highly encourage you to seek a Functional Medicine Practitioner. They will help you get to the root cause of your health frustrations and determine if fasting is appropriate.
As always, Trust in Your Gut.
Disclaimer: The contents of this article are for educational purposes only and are not intended to diagnose or treat any condition. Do not apply any of the information in this article without first speaking with your doctor.
References
- Kanazawa M, Fukudo S. Effects of fasting therapy on irritable bowel syndrome. Int J Behav Med. 2006;13(3):214–220. doi:10.1207/s15327558ijbm1303_4
- Tavakkoli H, Haghdani S, Emami MH, Adilipour H, Tavakkoli M, Tavakkoli M. Ramadan fasting and inflammatory bowel disease. Indian J Gastroenterol. 2008;27(6):239–241.
- Su J, Wang Y, Zhang X, et al. Remodeling of the gut microbiome during Ramadan-associated intermittent fasting. Am J Clin Nutr. 2021;113(5):1332–1342. doi:10.1093/ajcn/nqaa388
- Keshteli AH, Sadeghpour S, Feizi A, Boyce P, Adibi P. Evaluation of Self-Perceived Changes in Gastrointestinal Symptoms During Ramadan Fasting. J Relig Health. 2017;56(5):1620–1627. doi:10.1007/s10943–015–0160–0
- Hoddy, K.K., Kroeger, C.M., Trepanowski, J.F. et al. Safety of alternate day fasting and effect on disordered eating behaviors. Nutr J 14, 44 (2015). https://doi.org/10.1186/s12937-015-0029-9
