What is Intermittent Fasting?
Intermittent Fasting. You’ve most likely heard about it. It’s often scattered in amongst health conversations on topics like plant-based burgers, keto diets and morning rituals. Chances are also good that if you’ve suffered with chronic gut issues or spent any time around those who have, intermittent fasting is something you’ve come across.
In case you haven’t heard, intermittent fasting is a dietary strategy where you refrain from eating food for a specified length of time. It’s a return to a pre-agricultural practice of eating when food is available and fasting when it isn’t. Or it’s just the convenient way we justify skipping breakfast in this fast-paced life we live. In any case, fasting is an ancient fail-safe designed to boost our body’s resilience during conditions of starvation.
And we’ve fasted for millennia. Our bodies are literally designed for “feast and famine”.
Stowed away in the vast reaches of our DNA, nowadays we rarely unlock its potential. In fact, most of us will eat three meals a day (or more) for the rest of our lives. And the benefits don’t kick in until you skip a meal (or two). These benefits include a process of enhanced “cellular recycling” akin to spring cleaning, known as autophagy. Fasting also turns on powerful anti-inflammatory healing mechanisms within the body. We experience a sharp increase in our bodies production of antioxidants and we optimize our immune system.
There are different ways of using fasting for your health goals.
But can fasting improve your gut health?
This is exactly the question I aim to answer in today’s article.
Fasting: The Strategy of Our Ancestors
I’m not going to go into detail on all the health benefits of intermittent fasting here. But you can check out the interview I did with Scott Emmerson at Sandbox Fitness where we separate the hype and the science behind fasting.
OK let’s get into it.
Just to give you some brief background there are currently several methods of modern-day intermittent fasting. I’ll discuss three common ones today. Then we’ll dive into the rationale in using intermittent fasting for gut health.
In no particular order:
- Time-restricted feeding (TRF)
- Alternate day fasting (ADF)
- Prolonged fasting (24-36 hours)
Breaking Down the Fast
Time-restricted feeding involves daily fasting, while limiting feeding to certain hours of the day. Generally it involves at least 16-18 hours of fasting per day. The most common example of this is eating between 1-7pm. This would provide a 6 hour feeding window followed by an 18 hour fasting window. Pretty straightforward, right?!
Alternate day fasting on the other hand, involves a bit more planning. It requires you to know how many calories you put in your body on a daily basis as well. So here’s how it works: on one day you consume 25% of your normal caloric intake. So if we use the standard 2000 calorie diet that looks like 500 calories a day. I know what you’re thinking – tough right?! But on the second day you actually eat an additional 25% of your calories or 2500 calories. This pattern continues on an alternate day schedule, hence where it gets its name.
Finally, you can fast on a once weekly schedule for 24 hours or more. This means going an entire day without food! In my experience this option is less desirable but equally as effective as the other strategies.
Before we move any further please heed my caution: DO NOT ATTEMPT THESE STRATEGIES WITHOUT MEDICAL SUPERVISION
Ok, now that that’s out of the way let’s get to the good stuff – the gut!
Can Fasting Improve Gut Health?
It depends.
In order to understand how intermittent fasting may be helpful for those suffering with digestive issues, let’s look at what happens in the gut in between meals.
So there’s this thing we call gut motility. It’s the coordinated contraction of gut muscles essentially from “gum to bum”. And motility is controlled by the nervous system in the gut. This is known as the enteric nervous system. Proper motility is crucial for the movement of food, waste and bacteria through the digestive tract. Therefore, in most cases a disruption in motility will cause things to stop or slow down.
A major feature of gut motility is something called the migrating motor complex (MMC). This is a collection of nerve cells that coordinate contraction of muscles along the digestive tract. There are 4 phases of the MMC, each active at different times and each tasked with a specific function.
The Role of Gut Hormones
Gut hormones are also really important for intestinal motility. Two of these hormones are motilin and ghrelin. Aptly named, motilin is a hormone released during the fasted state that increases intestinal motility via the MMC. Ghrelin is released when we’re hungry and has a particular impact on gastric (stomach) motility and appetite.
You know that tummy grumble that creeps in around lunch time pleading with you to just eat something…anything!? Yeah, that’s the sound of gut motility in action! You see the hormones that stimulate appetite also stimulate the intestines to clear out. After all, we need to make room for the incoming food. Intermittent fasting taps into this system. It does this by stimulating hunger and the subsequent release of gut hormones. So from a physiological standpoint this makes sense.
Does it work in real life though?
Fasting and Digestive Disorders: Does it Make Sense?
One condition that may benefit from this unique feature of fasting is small intestinal bacterial overgrowth. Although there are many causes of SIBO, it often results after damage to the MMC occurs. This impairs our ability to clear out bacteria from the small intestine. This leads to an overgrowth of bacteria and stubborn symptoms like gas, bloating, diarrhea and/or constipation. One popular strategy of SIBO treatment simply involves spacing out your meals. Allowing 4-5 hours between meals can theoretically improve MMC function, although there is no evidence to suggest this works.
If you really want to stimulate and restore the MMC acupuncture or electroacupuncture is a pretty effective way to do it, according to research.
Starving the Bugs
SIBO often overlaps with Irritable bowel syndrome (IBS) which is super common. One of several ways intermittent fasting might improve symptoms is by providing bowel rest. A diet low in fermentable carbohydrates (AKA a Low FODMAPs diet) is a well known treatment for IBS. It works by reducing the amount of carbohydrates that bacteria can feed on and ferment. This results in a reduction in gas and water in the bowels, which lessens pain and reduces diarrhea. In a similar manner, fasting accomplishes the same thing. It provides a much needed break for overly-sensitive gut nerves. Check out Wired Brain, Wired Gut? to learn more about how sensitive gut nerves cause symptoms in gut disorders.
Intermittent fasting can also reduce inflammation and regulate immune cells. Overactive immune cells and low-grade inflammation in the gut are typically present in IBS.
Interestingly, intermittent fasting can help with nerve regeneration in multiple sclerosis patients with mild disease and in diabetics. This could potentially benefit a number of digestive disorders including diabetic gastroparesis, IBS, and SIBO.
At this point we don’t actually have any studies to validate these theories or the benefits of fasting in digestive disorders. And while this is true, here’s what we do know:
Fasting Improves Gut Bacteria
It’s true. Fasting can improve certain species of bacteria that are associated with health outcomes. This has been a consistent finding in studies looking at the impact of fasting on the microbiome.
In fact, just recently intermittent fasting was put to the test in a clinical trial. The researchers wanted to see if intermittent fasting would influence the growth of beneficial bacteria in the gut. It turns out they were right. They found two species were significantly increased: Akkermansia mucinophila and Bacteroides fragiles. That may not mean much to you but these two species are known to have significant health-promoting effects. Akkermansia for example, helps maintain the health of the intestinal barrier.
That’s not all.
Something called the Firmicutes:Bacteroides ratio, a well known microbiome marker for overall health is improved with intermittent fasting. Obesity and metabolic syndrome are associated with less favorable ratios.
Investigators have also determined that some of the health benefits of fasting, like improving fatty liver and obesity are attributed directly to gut bacteria. As it turns out, those health benefits are wiped out when mice fast in the absence of any gut bacteria!
Clearly we are just scratching the surface on this topic; however, in many chronic disease states if you improve the microbiome, you improve the health of the person.
But…
Before we all rush to the fasting table, let’s have a discussion on what to watch out for.
Fasting for Everyone? Not so much…
There are caveats to fasting.
First and most importantly, not everyone should do it.
People prone to dysglycemia or irregular blood sugar levels will struggle with fasting. Similarly, Type 1 and 2 diabetics absolutely need to be closely monitored by a professional to avoid life-threatening complications like hypoglycemia.
For those with moderate to severe inflammatory bowel disease, this isn’t for you either. Not now anyway.
People with a history of an eating disorder should not attempt intermittent fasting.
What About my Adrenals?!
Other exceptions include those with hypothalamic-pituitary-adrenal-thyroid problems. What’s this you ask??
This can manifest as the following symptoms:
- Low energy/burnout
- Low resilience to stress
- Frequent infections and immune challenges
- Significant hair thinning, falling out or very dry skin
- Cold intolerance
- Insomnia
- Weight gain
Why? because intermittent fasting works because it stresses your body into adaptation. If you’re already under a tremendous amount of stress then there’s no more room for adaptation! This can cause the symptoms mentioned above. It can generally cause people to feel lousy and defeated because they didn’t respond like “everyone else”. If this applies to you then it may be necessary to support those systems first before considering intermittent fasting or it might make them worse.
If you do decide to give fasting a try you need to watch out for these potential side effects.
Side Effects of Intermittent Fasting:
- Binge eating leading to weight gain
- Worsening of sleep patterns
- Mood swings
- Increased cravings
- Low energy
- Dangerous blood sugar swings (hypoglycemia)
- Changes in electrolytes (if not hydrating properly)
- Constipation – “but he said…” – yeah, it can possibly worsen digestive symptoms too
Final Thoughts on Fasting
Fasting is no longer an ancient survival tool solely relied on by those in search of their next meal. Intermittent fasting has demonstrated numerous potential health benefits for our current ailing society.
While researchers aren’t yet testing the effects of intermittent fasting for the treatment of digestive disorders, an argument could be made for them to do so. In fact, we see several beneficial changes in gut bacteria of fasted mice and humans. Improvements in obesity, nerve regeneration, and inflammation are largely attributed to the changes in our gut bacteria. In turn, these changes could lead to improvements in the structure and function of the gut itself!
We’ll have to wait and see how this all unfolds. Fasting may become an important strategy for gut health.
Fasting, while an extremely attractive and popular dieting strategy, needs to be implemented carefully and professionally. It’s not for everyone. And yes, it may have side effects or unintended consequences. If you are curious to learn more about whether intermittent fasting may be right for you, let’s have a chat!
References:
Özkul, Ceren, Meltem Yalınay, and Tarkan Karakan. “Islamic fasting leads to an increased abundance of Akkermansia muciniphila and Bacteroides fragilis group: A preliminary study on intermittent fasting.” The Turkish Journal of Gastroenterology 30.12 (2019): 1030.
Stockman, Mary-Catherine, et al. “Intermittent fasting: Is the wait worth the weight?.” Current obesity reports 7.2 (2018): 172-185.
Cignarella, Francesca, et al. “Intermittent fasting confers protection in CNS autoimmunity by altering the gut microbiota.” Cell metabolism 27.6 (2018): 1222-1235.
Yin, Jieyun, and Jiande DZ Chen. “Gastrointestinal motility disorders and acupuncture.” Autonomic Neuroscience 157.1-2 (2010): 31-37.