• Allison Fahrenbach

Improve Your Gut Health with Fasting

I am going to start this blog with a quote:


“I’m convinced that the best solutions are often the ones that are counterintuitive – that challenge conventional thinking – and end in breakthroughs” Nathaniel J. Wyeth


I love this quote because it helps me to approach my coaching practice with an open and inquisitive mind, and to entertain all methods and protocols, both in my own health efforts and in helping my clients with theirs.


But as much as I like quotes, I like science more. And when it comes to implementing fasting to optimize digestion, heal the gut and manage IBS, there’s lots of it. Fasting may seem counterintuitive, but the body does quite a few amazing things when you aren’t fed. I’ll explain what those are, as well how fasting differs from simply “not eating.”





Digestion Requires Effort

To understand how fasting works, you first need to understand the amount of work your body has to do when you eat. When you eat a meal, or take in food, your body has to go about dismantling, or breaking that food apart into the nutrients it needs. Once a food is broken down, it then has to get to work assimilating and absorbing those nutrients.


These processes are actually pretty laborious and require about 25% of the total calories you consume from each meal. Furthermore, when you digest food, your body shifts its focus and resources away from other important physiological processes, such as growing and repairing. Simultaneously your immune system also has to be on alert, screening what passes through the gastrointestinal tract.


If you eat 3 meals a day, and have a few snacks in between, then chances are your digestive system doesn't get much time off. It’s only after about seven hours unfed that your body is physiologically in a fasted state.


If you’re thinking right now, its not often that 7 hours goes by without at least a calorie containing beverage, snack or meal (in daylight hours at least), you’re not alone. This is true for most of us.


But anything that has to be metabolized will shift your gene expression away from a fasted state.


So what is it about fasting that is so beneficial for the health of the gut?


It synchronizes your gut circadian rhythm

I am sure you’ve heard of the term “circadian rhythm”, the natural, internal process that regulates the sleep-wake cycle and repeats every 24 hours.


But did you know that your gut microbiome has a circadian rhythm too? Different types of microbes fluctuate in abundance and activity throughout day and night. This fine balance can be disrupted when the human circadian clock is affected, thus compromising metabolic health.


A 2014 study in mice, revealed that fasting improved the diversity and circadian cycling of gut flora.

It boosts microbiome diversity

A diverse microbiome is a healthy microbiome, and fasting can help to improve your microbial diversity.

In a recent study performed on patients suffering from multiple sclerosis, an increased abundance of the following microbial families was observed after 4 weeks of fasting:

  • Bacteroidaceae

  • Lactobacillaceae

  • Prevotellaceae

  • Faecalibacterium

Among these, it is important to highlight the importance of Lactobacillus, which is a well-known probiotic strain that has been recognized for its multiple benefits on gut health. Lactobacillus contribute to a balanced microbial ecosystem by aiding nutrient digestion and absorption, metabolizing indigestible compounds, inhibiting pathogens, and stimulating the immune system


Another appealing finding in this study was the enrichment in Faecalibacterium. Science has linked individuals lacking sufficient amounts of this bacteria with chronic constipation, Celiac Disease, IBS, and IBD (Crohn’s Disease and Ulcerative Colitis). Faecalibaterium not only relieves IBS, IBD and regulates gut motility, it also has anti-inflammatory effects (increasing the level of anti-inflammatory cytokines), empowers intestinal barrier function, and influences mucus production in the gut.


Inflammation & Oxidative Stress

Fasting reduces oxidative stress (the damage that occurs to cells from exposure to toxicity).


Interestingly, the development of IBS is linked to increased levels of oxidative enzymes, and reduced activity of antioxidant enzymes. This is what causes progressive damage to your cells, retarding their function.


Cells matter, after all they make up the organs which handle digestion. Progressive damage to even one organ in the digestive system can throw the whole process out of line, producing symptoms of IBS.

But when you fast, you allow for a process called autophagy which is the process by which you’re body clears out damaged cells, in order to regenerate newer, healthier cells. “Auto” means self and “phagy” means eat. So the literal meaning of autophagy is “self-eating.” It’s also referred to as “self-devouring.” While that may sound like something you never want to happen to your body, it’s actually beneficial. In fact it’s a built in evolutionary self-preservation mechanism through which the body can remove dysfunctional cells and recycle parts of them toward cellular repair and cleaning. It’s like hitting your body’s reset button. Because fasting allows for the body to run this process, it’s a powerful intervention for IBS, IBD and leaky gut.


Fasting & The Migrating Motor Complex (MMC)


The migrating motor complex (MMC) is one of the body’s most important mechanisms for optimal digestion. This mechanism refers to the periodic cyclical pattern of contractions that occur in the upper gastrointestinal (GI) tract (stomach and small intestine) during an unfed state.


Think of the MMC as the housekeeper of the GI tract. It comes along in between meals and “sweeps out” bacteria and undigested food particles for elimination. 

MMC activity peaks in between meals, in the absence of food. The presence of food and nutrients interrupts and decreases MMC activity, and essentially steers hormonal control back towards digestion and assimilation. 

So when you periodically fast or have unfed windows of time during the day it gives the MMC the time and space it needs to thoroughly do its job.

This is why fasting can even help protect against bacterial imbalances like SIBO. While the relationship is correlational not causative, science has connected patients with SIBO to absent or disrupted MMC patterns.


Science has also connected IBS patients with shortened periods of MMC activity.


Improves Symptoms of IBS

There is only one study (that I know of) that has investigated the direct effects of fasting as it pertains to IBS specifically. The results were promising. 36 subjects underwent fasting therapy for a period of 10 days and were progressively re-fed for 5 days after.


Compared to the 22 subjects in the control group (conventional pharmacotherapy), the fasted group reported a significant improvement in symptoms. The symptoms were abdominal pain-discomfort, bloating, diarrhea, anorexia, nausea, anxiety, and interference with life in general.


Although the 10 day controlled fasting protocol used by this study is not really feasible for most people this does indicate that fasting has a beneficial impact on IBS symptom reduction.


Fasting increases Akkermansia muciniphila and fights infection

A 2018 study investigated the impact of fasting on mice infected with Salmonella typhimurium.


This study indirectly indicates that fasting can help manage IBS and IBD because this particular bacteria can cause acute colitis in as early as 12 hours after contamination. In this study, mice were infected with this bacteria to induce acute colitis, then separated into two groups. One group was fed for 24 hours and the other group fasted. The results were remarkable: fasting eliminated S.typhimurim infection and colitis. This is thought to be due to the deprivation of the pathogenic bacteria from nutrients, which in turn reduces its ability to trigger an inflammatory response.

The fasting group also exhibited a greater diversity in their microbiome, particularly an increase in the genus Akkermansia, which has been shown to reduce fat mass gain and to improve gut barrier function and glucose metabolism.

How to put it into practice

You don’t have to starve yourself to fast. Think of fasting less as starving and more as a strategic way of eating. Starving deprives the body of major nutrients, and can cause nutritional deficiencies, but fasting on the other hand, suggests that you eat the right things at the right time, not that you shouldn't eat at all,


There are actually a lot of ways to fast, which makes it easy to experiment and find a method that works well for you.


You could start with:

  • 12 hours fasted // 12 hours fed

  • 14 hours fasted // 10 hours fed

(I personally go unfed 12-14 hours a day. I eat dinner around 6/6:30 pm and breakfast the following day at 8 am. I do this daily and have for years.)


If you get comfortable with 12-14 hours fasted you could then progress onto:

  • 16 hours fasted // 8 hours fed (repeat every other day)

  • 16 hours fasted // 8 hours fed

  • 19 hours fasted // 5 hours fed

  • 20 hours fasted // 4 hours fed 

  • 1 day fasted // 6 days fed

You can also choose any of these and do them intermittently, mixing up the windows which you eat in. Play around and see what works for you.


You can also try prolonged fasting:

  • 24 Hours – from dinner to dinner / lunch to lunch. You effectively eat once/ day which you can do a few days/week.

  • 36 Hours – eat breakfast on day 1, then fast for all of day 2 to eat breakfast again on day 3. You may choose to do this 1 maybe 2 times a week initially for a big gut healing push. Then continue with shorter fasts.

  • Fasts beyond 48 hours can be done but require support with micronutrients and supplements. I’d encourage professional support and supervision with these

If you want help figuring out how best to implement fasting to optimize your health, I'd love to help!.

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