Intermittent Fasting can improve Gut Health
1. Improve Gut’s Circadian Rhythm
Our gut, like our body, operates on a circadian rhythm also known as sleep-wake cycle. To produce uninterrupted energy, our metabolism continuously switches between using sugars during the day and fats at night.
Side note, scientists are still learning about this complex process that activates specific genes, adjusts hormones (insulin during day, melatonin at night), and times during energy production (maximizing mitochondrial activity). 
What we know for sure is, a healthy metabolism is a flexible one, capable of adjusting its activities and energy based on the time of the day.
Take insulin as an example; a hormone that triggers energy storage by moving sugar out of bloodstream into cells. Insulin is most effective during the morning and midday, and less so in the late evening and night time.
Therefore, late snacking triggers a less functional insulin response resulting in longer lasting elevated blood sugar levels. Because such habits fall outside the optimal circadian eating window, they can increase our risk for metabolic diseases including type 2 diabetes, cardiovascular disease and even some cancers. [9,10]
Intermittent fasting eating windows often fall within sleep-wake cycles, thus improving insulin sensitivity and reversing any metabolic inefficiencies.
2. Boost Microbiome Diversity
As part of our metabolism, gut microbes also do better when aligned with the circadian rhythm. [11,16] Microbiome fluctuates from what we eat (diet) as well as when we eat.
For example, high fat diet lowers Bacteroidetes phylum bacteria while increasing cultures within Firmicutes phylum—changes associated with obesity. [11,12] Bacteriodetes digest wide range of proteins and complex sugars; while Firmicutes are involved in energy reabsorption.
Reducing late night eating and extending fasting periods can produce various wellness benefits including weight loss and healthier gut microbiome. [11-13]
Fasting not only modifies gut flora but also improve their effectiveness, which reduces inflammation and lower rates of digestive diseases. [12-13,18] Bad bacteria are more sensitive to fasting which slows down their growth (reproduction).
Fasting can even help fight pathogenic strains (like Salmonella typhimurium) eliminating unhealthy gut symptoms altogether.  Hence, fasting can aid in making good gut bacteria more resilient while relieving digestive issues.
Eating wide varieties of foods further helps with increasing microbiome diversity, which is a win-win. 
3. Strengthen Gut Barrier
Digesting food on daily basis is hard work, and doing so continuously can be exhausting. Fasting provides the digestive tract time to rest and restore some of its integrity.
Fasting allows time to fix issues such as “leaky gut” (or intestinal permeability), where gut lining is weakened allowing toxins, food particles and even pathogens to slip through and enter bloodstream. If untreated, leaky gut can trigger an inflammatory response like endotoxemia, leading to several metabolic and immunity risks. 
Furthermore, fasting can strengthen the gut barrier, lowering intestinal inflammation and reducing symptoms of gut related issues such as inflammatory bowel disease (IBD).  Stronger gut barrier further enhances conditions for good gut bacteria to live, grow and function.
4. Helps Gut Motility—Migrating Motor Complex
Gut motility is the movement of food through the GI tract. This process is regulated by migrating motor complex (MMC), a system of nerves in the intestines which synchronize wave-like contractions throughout the digestive system.
MMC acts as GI’s housekeeping system, helping with nutrient absorption and removal of overgrown bacteria from small intestine into the colon. Malfunctioning MMC produces discomforts like bloating, irritable bowel syndrome (IBS) or functional dyspepsia (FD). 
MMC occurs only during fasting (not eating), that is between meals or during sleep. Fasting enhances MMC and strengthens digestive processes, maintains a healthy gut flora while reducing inflammation and other related gut discomforts. [17,18]
This is why “when” we eat has become as important as “what” we eat. Coupled with a balanced diet comprised of fiber, pre- and pro-biotic foods, fasting can further digestive benefits such as insulin sensitivity, mitochondrial function, tissue repair, immune response as well as reducing bad gut bacteria and inflammation.