I trust the recent evidence on gut health benefits from fasting and time-restricted eating because systematically refraining from food helped me heal my leaky gut when I was younger.

A person waiting to break her fastPhoto byAmir Abbaspoor from Pexels

This story does not include health advice. It is for information, inspiration, and awareness purposes.

Like billions of religious people throughout history, I have secularly known the benefits of fasting in gut health for a long time, as fasting helped me to heal my leaky gut (intestinal permeability). I also helped and inspired several relatives and friends to fix their leaky guts using time-restricted eating with support from their family doctors, who endorsed and guided their eating regimens. I wrote a summary of a case study in 2022. Fasting is now mainstream.

You may wonder what science says about it and whether these anecdotes are backed up by scientific studies. That’s why I wrote this short story: to give you valuable perspectives based on my intense research from growing literature. My goal is to inform my readers with evidence-based information from credible sources.

Emerging evidence in the growing literature suggests that time-restricted eating may positively impact human gut health, particularly by increasing microbial diversity, potentially influencing the abundance of beneficial bacteria, and removing harmful pathogens.

I read hundreds of papers that have covered the effects of calorie cutting and time-restricted eating in animal studies impacting gut health, but recently, clinical studies in humans have started and given us valuable clues on the effects of fasting on our gut health. Our gut is critical for linking to all organs, including the brain. I covered the brain-gut axis before based on my research. I also covered gut-lung connections within the context of the adverse effects of COVID-19 on digestive health.

A comprehensive study in Nature in 2021 informed that fasting caused significant changes in gut bacteria and the immune system, with some changes persisting even after the fasting period ended. It appears that fasting might “reset” the microbiome and immune cells, making them more responsive to the healthy diet that followed.

The researchers suggest that increased availability of short-chain fatty acids (SCFAs), produced by gut bacteria, may be a key factor in the blood pressure improvement. They also found that specific immune cells and gut bacteria were linked to blood pressure changes.

Using machine learning, the researchers could even predict who would benefit most from the fasting intervention based on their initial immune system and gut bacteria profiles.

The study provided promising and convincing evidence that fasting, combined with a healthy diet, could be an effective non-pharmaceutical way to improve gut health. However, they said more research was needed to confirm these findings and explore the long-term effects.

Fasting’s impact on the microbiome and gut health is a complex and evolving area of research, with findings suggesting both potential benefits and areas of caution. Several studies indicate that fasting, particularly intermittent fasting, can increase the diversity of gut bacteria, which is generally associated with better health outcomes.

Numerous studies also mentioned that intermittent fasting may promote microbial remodeling, leading to changes in the types and abundance of specific bacteria in the gut. This could have positive effects on metabolism and inflammation. Fasting may also enhance the integrity of the gut lining, potentially reducing inflammation and improving overall gut health.

The effects of fasting on the microbiome vary significantly depending on the person, the specific fasting method (time-restricted eating, alternate-day fasting, intermittent fasting, etc.), dietary habits, and baseline microbiome composition.

Some studies speculated that changes in the gut microbiome during fasting may be temporary and revert to baseline after the fasting period ends. However, new studies have shown contrary results, which I will cover in this story.

Rather than going into details of many papers, I want to summarize the findings of a 2024 systemic review, citing 80 high-quality papers out of 1300 studies and intensely examining eight outstanding ones. This is, so far, the most comprehensive, up-to-date, and credible analysis of this topic from my reviews. Frontiers is a reliable and peer-reviewed journal. This research is valuable because millions of people are impacted by gastrointestinal disorders that are widespread globally.

Today, I wrote this story on an empty stomach after 48 hours of fasting in mild ketosis, giving rest to my digestive system to inspire my readers. I shared my long-term fasting experience before, like ten days, giving me 7.3 mmol/L BHP (beta-hydroxybutyrate), which is the main ketone produced by the liver and used by the brain, the heart, and the gut. I explained ketogenesis and beta-hydroxybutyrate before.

Health Benefits of Fast-Induced Gut Microbiota Changes

The paper, which was published in Frontiers Nutrition journal on 12 February 2024, conducted a comprehensive literature review. They investigated 1300 studies from Cochrane Library, PubMed, Scopus and Web of Science.

Their criteria focussed on eight high-quality studies, including randomized controlled trials, quasi-experimental studies, and pilot studies that investigated the effects of intermittent fasting on gut bacteria in both healthy people and those with various diseases.

The research team reviewed data from each study about the types and amounts of gut bacteria before, during, and after intermittent fasting. They also gathered information about the participants’ age, health conditions, weight, and diet. If any details were missing or unclear in the original studies, the research team noted them in their review to avoid making assumptions.

Eight studies examined how intermittent fasting affects gut bacteria. Six measured the number and variety of gut bacteria (richness and alpha diversity), while five measured how gut bacteria changed over time and between groups (beta diversity).

All eight studies looked at the types of bacteria present in the gut. I’d like to highlight that only two studies provided specific numbers for gut bacteria diversity, while the rest presented their findings using diagrams.

In a study with healthy males, they found that principal component analysis showed distinct microbiome communities in the time-restricted eating and control groups after 25 days.

In healthy adults, microbial community structure (beta-diversity) significantly differed pre- and post-Ramadan. For example, Pakistani participants showed substantial divergence in microbial composition post-Ramadan, unlike slight shifts in Chinese participants.

Gut microbiota in healthy young and middle-aged cohorts also changed significantly during Ramadan but returned to baseline after fasting, indicating reversibility. The middle-aged non-fasting control group showed no changes, confirming gut microbiome stability without lifestyle changes.

In a 5:2 diet study with metabolic syndrome patients, microbial community composition shifted significantly within this fasting diet group after eight weeks, while no significant changes were seen in the control group.

Overall, these studies indicated that intermittent fasting (IF) can change the diversity and composition of gut microbiota, which may be beneficial for conditions like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS).

By the way, IBD and IBS both affect the digestive system but differ significantly. IBD, including Crohn’s Disease/Ulcerative Colitis, involves chronic inflammation and can cause damage to the GI tract. IBS is a functional gastrointestinal disorder characterized by symptoms like abdominal pain, bloating, gas, alternating diarrhea, and constipation without causing inflammation or permanent damage.

These researchers analyzed alpha and beta diversity, which I will explain in the next section. Higher diversity is linked to better health and stability in the gut ecosystem. Low diversity is usually found in various diseases, while high diversity usually includes more beneficial anaerobes.

What attracted my attention in this review was compositional changes in specific bacteria types during intermittent fasting and their impact on health. They categorized findings under three sections.

The first section included Negativicutes, Selenomonadales, and Veillonellaceae. These bacteria are often found in higher amounts in people with IBS and IBD. Intermittent fasting helps decrease their abundance, which may reduce inflammation and improve gut health.

The second section included Proteobacteria and Gammaproteobacteria. Higher levels of these bacteria are linked to dysbiosis (gut imbalance) and inflammation. An increase in these bacteria could be harmful, as they are associated with metabolic disorders and IBD. However, some nuances are covered in the next section.

The third section included Clostridiales and Faecalibacterium. I found this section extra valuable because Faecalibacterium, a key producer of butyrate (an anti-inflammatory compound), benefits gut health. Intermittent fasting can increase the abundance of Faecalibacterium, which can help reduce inflammation, improve IBD, and even contribute to cardiovascular health.

I pay great attention to butyrate and follow the research closely. For example, in 2022, researchers published a comprehensive review on Frontiers titled “Role of Butyrate, a Gut Microbiota Derived Metabolite, in Cardiovascular Diseases.”

A 2015 study in Nature pointed out that activation of HCAR2 (hydroxycarboxylic acid receptor 2, a protein-coding gene) in the gut epithelium by short-chain fatty acids like butyrate activates the NLRP3 inflammasome and maintains gut membrane integrity. Butyrate has essential roles in maintaining gut health, regulating inflammation, and providing energy to colonocytes.

So when considering bacteria that changed significantly in at least three studies, Proteobacteria, Gammaproteobacteria, Clostridiales, and Faecalibacterium increased, while Negativicutes, Selenomonadales, and Veillonellaceae decreased. In terms of good and bad bacteria, these findings suggest that intermittent fasting may lead to an increase in certain beneficial bacteria while decreasing potentially harmful bacteria

In summary, intermittent fasting can enhance gut microbiota diversity and beneficial bacteria while reducing harmful bacteria linked to inflammation. These changes may support better gut health and help manage conditions like IBD and IBS.

It would have been beneficial if they had the opportunity to examine leaky gut syndrome, especially through genomic analysis. You can learn about the genetic aspects of some harmful bacteria from this paper.

Difference Between Alpha and Beta Diversity

In the context of gut microbiota, alpha and beta diversity are two ways of measuring the variety of bacteria present.

Alpha diversity focuses on the diversity within a single sample or person, measuring the number of different types of bacteria present and their relative abundance.

Higher alpha diversity generally indicates a healthier gut microbiome with greater disturbance resilience, with examples including the Shannon Index, Simpson Index, and Observed OTUs. These indices help researchers assess and compare the complexity of microbial communities, providing insights into ecosystem health and function.

Beta diversity, on the other hand, focuses on the diversity between samples or groups of people, measuring the differences in bacterial composition between them.

Higher beta diversity indicates greater differences in the types of bacteria present between samples or groups, with measures such as Bray-Curtis dissimilarity and UniFrac distance.

An analogy would be a forest: alpha diversity is like counting the number of different tree species within a single plot of land, while beta diversity is like comparing the types of trees found in two different forests.

Conclusions and Takeaways

While promising, scientists are still investigating the impact of time-restricted eating or fasting on gut health. Human studies have shown potential benefits, like increased gut bacteria diversity linked to better health. However, these effects can vary widely depending on personal factors, and some studies have found no significant changes.

It is crucial to approach fasting cautiously and consult qualified healthcare professionals, especially if you have underlying health conditions. Fasting does not suit everyone, especially pregnant women, children, and sick people. It might also have side effects initially. More research is needed to fully understand the complex relationship between fasting, the gut microbiome, and overall health.

Despite these unknowns, some studies have shown positive results, such as an increase in beneficial bacteria like Faecalibacterium, which produces butyrate, a nutrient for the gut lining. Additionally, some research has shown increases in Akkermansia, a bacteria linked to improved metabolic health.

As research continues to reveal the complexities of this relationship, it’s clear that time-restricted eating, also known as intermittent fasting, holds the potential for improving gut health, but further studies are needed to confirm these findings and establish optimal approaches for different groups of people by replicating them in larger clinical studies.

Metabolic health and gut health are intricately connected. Some studies have shown that time-restricted eating improves insulin sensitivity, a key factor in blood sugar regulation and prevention of type 2 diabetes. This improvement in insulin sensitivity may be linked to changes in the gut microbiome.

While research on fasting’s impact on gut microbiota is still emerging, it depicts potential benefits. Notably, there is no evidence to suggest that fasting harms gut health. Historical accounts of millions benefiting from fasting further support its potential. Therefore, it is crucial to approach fasting with an open mind and experiment cautiously and under healthcare professionals' guidance.

Beyond potential benefits to the gut microbiome, fasting may offer a crucial advantage: giving the digestive system a chance to rest and repair itself. This period of digestive dormancy may promote healing, particularly in conditions like leaky gut syndrome, as supported by emerging research and personal evidence like my case.

Over the last decade, the scientific community has witnessed a surge in research interest surrounding the potential health benefits of fasting. This growing body of evidence, highlighted in a comprehensive review published in the prestigious medical journal The Lancet earlier this year, has captured the attention of both researchers and the general public, solidifying fasting as a promising avenue for improving health.

The True Science Behind the Health Benefits of Time-Restricted Eating, Including 23 Quality Clinical Trials

Thank you for reading my perspectives. I wish you a healthy and happy life.

If you found this story helpful, you may also check out my other articles on NewsBreak. As a postdoctoral researcher and executive consultant, I write about important life lessons based on my decades of research and experience in cognitive, metabolic, and mental health.