Module 3.5: Intermittent Fasting

Intermittent fasting (IF) has several benefits physiologically, including modulation of the GM, that I believe are helpful in fighting inflammatory bowel disease or other digestive issues (36,37). Research regarding the exact mechanisms and effects that IF has on the GM are still ongoing, however, there are animal and human trials that suggest that different types of fasting and calorie restriction improve the composition of the GM (36,37,38). The findings of one particular murine trial, where the mice had colitis induced with dextran sodium sulfate (DSS), showed that an 8 hour feeding window immediately followed by a 16 hour fast was able to improve the GM by decreasing the growth of the pathogenic microorganisms Shigella and E. coli and increasing the growth of several probiotic microorganisms, including Lactobacillus (38). Mice in the calorie restriction group, which is another type of fasting, experienced the same GM improvements. As a result of the GM improvement, the mice in both the 16:8 IF group and the calorie restriction group saw a strengthening of their tight junctions, which helped to correct their leaky gut, an increase in SCFA production, which helps to reduce inflammation, and ultimately resulted in mice from both groups having significant levels of reversal in the development of colitis (38,39).

In an eight week randomized controlled trial (RCT), the effects of IF on cardiometabolic risk factors and the gut microbiome were tested on 39 patients diagnosed with metabolic syndrome (37). The results of the trial showed that short-term two-day IF not only helped improve cardiometabolic health, but it also induced a eubiotic effect that helped push the GM towards homeostasis (37). IF exerted this eubiotic effect on the GM by increasing the levels of probiotic microorganisms; one in particular known as Roseburia (37). This genus of bacteria is known to produce the SCFA butyrate (37). Butyrate is a well-known SCFA that is an important energy source for colonocytes, and it is important in the regulation of TJ proteins (40,41). Low butyrate production is thus logically suspected to contribute to the pathogenesis of IBD, specifically UC (18). Overall, the study concluded that IF improves the composition of the GM by increasing beneficial microorganisms and SCFA production, and decreasing certain bacteria that are associated with cardiometabolic dysfunction (37).

So, IF seems to have a pretty positive impact on the GM, and is thus an excellent tool that can be used on our quest to optimize it. I personally followed a 16:8 IF regimen just like the mice did when I was going through the GM optimization process, so I ate all of my food in an 8 hour window and then fasted for 16 hours every day. My feeding window was generally between 1:00pm-9:00pm every day, but this can be customized to whatever best fits your schedule.

IF doesn’t just benefit the GM, it can also help lower the total amount of BMs an individual has per day. I first started IF in an attempt to optimize my testosterone levels which had significantly decreased in the months after being diagnosed with IBD (42). I was happily surprised when I realized that IF wasn’t just helping with my hormones, but it was also causing me to have less BMs per day than usual because I was triggering the gastrocolic reflex less times per day. The gastrocolic reflex is a reflex that results in the urge to defecate after eating or drinking something, so that the body can make room for incoming food or drink (43). This reflex is triggered when stretch receptors in the stomach sense that food or drink is causing the stomach to expand (43). This is a normal and healthy function for most people, however, it’s been noted that people with IBS have a stronger colonic response and a stronger urge to poop after the gastrocolic reflex has been triggered (43). I believe that IBS is a precursor to IBD based on what I’ve read and my understanding of the cascade that I think leads to IBD (44). And from personal experience, I know very well that I suffered from a heightened and exaggerated gastrocolic reflex while sick with IBD. If you’re battling IBD and have ever found yourself sprinting to the toilet trying your hardest to hold in explosive diarrhea immediately after eating or drinking something, and not knowing if you’re going to make it- then you know what I’m talking about. The point is, the gastrocolic reflex seems to be extremely sensitive for people suffering from IBS and IBD, and eating several times throughout the day will trigger that hypersensitive reflex and increase the number of times you’re racing to the toilet.

However, if IF is incorporated, and only 1 or 2 calorie-adequate meals are consumed each day, then the gastrocolic reflex should only be triggered once or twice per day, which should help to decrease the total number of daily BMs. This was really effective for me personally.

So in summary, IF has GM optimizing potential and it can significantly reduce the number of BMs per day by lowering the number of times the gastrocolic reflex is triggered.

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