The Impact of Fasting on Your Microbiome



We are now beginning to understand and know how powerful the composition of microflora in your gut can be a major factor in the development of many illnesses. Historically, cultures throughout the world have incorporated fermented foods (sauerkraut, kimchee, yogurt, etc.) into their traditional diets to re-establish and maintain a healthy probiotic (friendly bacteria) profile. The gut microbiome is a hot-topic, and because of this, fermented foods, foods with added probiotics, and probiotic supplements are continuing to grow in popularity.

Another area of growing interest in the optimization of gut health is the use of fasting as a tool to promote a healthy gut microbiome and therapeutically support chronic conditions that range from eczema and migraines to obesity and metabolic syndrome.

Fasting stresses your body in a benevolent way and that “good” stress turns on autophagy, which is the body’s natural cellular detoxification process contributing to chronic disease prevention as well as longevity. I am incredibly passionate about the benefits you can achieve through fasting. Let’s explore!

Intermittent Fasting and Autophagy

Many people graze periodically throughout the day which doesn’t give cells a chance to do their job of repair and clean-up of the waste and toxins that have accumulated. For some, the mere mention of the word “fasting” conjures up feelings of extreme hunger and they scorn the practice. But there are many different types of fasts and the merits of fasting are definitely worth exploring for everyone.

Throughout history, fasting has been an important health-promoting component of many religious and spiritual practices. Today, there are many different types of popular fasts used as a means to promote natural health and wellness. Additionally, the therapeutic benefits of fasting are now readily recognized in medical literature.

Fasting practices range from eating nothing or very little for a certain amount of time to consuming only water for a set period (sometimes up to five days) as a means of therapeutically “healing” the gut.

A more practical approach for everyone is Intermittent Fasting (IF) — the practice of shifting between periods of unrestricted eating and restricted eating — meaning that you go short intervals of time without eating food. Research suggests that 16 hours is the optimal amount of time for creating the caloric restriction that happens during fasting and to also activate autophagy, giving your cells a chance to take out the trash. I personally practice this strategy and highlight its merits in my bestselling book, Glow15.

There is also the 5:2 diet, where someone eats a “normal” diet for five days, and then cuts intake down to one-quarter of their usual intake for the remaining two days. Each of these strategies has their own supporters, but the commonality of all types of fasting is to give your hard-working gut microbes a break from their main duty of digestion, so they can focus on cleaning house and keeping their populations intact.

Dr. Valter Longo of the Longevity Institute at the University of Southern California is a leading expert in the study of the “fasting mimicking diet” (FMD). His research ties together well-designed studies in cellular biology with animal studies and human trials to provide an explanation for the numerous benefits of fasting, such as:

  • lowering visceral fat
  • reducing cancer rates
  • improving the immune system
  • slowing down the loss of bone mineral density
  • increasing longevity

Results from a June 2018 study align with previous research on other types of IF diets suggesting metabolic benefits. But, it also suggests that the 16:8 diet may be easier for people to maintain when compared to other fasting diets. This is a huge benefit as the problem with many current diet trends is they are not sustainable.

What Happens in the Body When You Fast?

Glucagon is a hormone released by the pancreas in response to low blood glucose, whereas insulin works in opposition to reduce blood glucose levels. When you fast intermittently, insulin levels go down and glucagon goes up which has been shown to have benefits like increased metabolism, more energy, improved mood, and weight loss.

Fasting can also increase the diversity of bacteria in your gut, which is important for your immune and overall health. Researchers have linked daily fasting to activation of the gene that strengthens the gut barrier to protect us from harmful microbes, toxins, and other substances that can trigger immune reactions.

In addition, IF helps restore the integrity of the intestinal lining, favorably influencing the inflammatory response contributing to protection against the traffic jam of chronic diseases linked to inflammation. The point is that when you fast you win on many levels! You increase your autophagy and get rid of the gunk. Your gut health improves, you reduce your risk for many chronic diseases AND you look and feel better.

Linking Gut Microbiome Health to Fasting

A healthy gut microflora is pertinent to digestive health which directly influences your immune health, your hormones, neurotransmitters, nutrient status, mitochondrial function, adrenal status and most importantly, whether or not your inflammatory response works for or against your health. And vice versa: your hormones, neurotransmitters, nutrients status, mitochondrial and adrenal status, and inflammatory response all impact your gut.

When bad bacteria take over, the ability to repair gut health is impaired which can lead to a whole host of problems. Scientists are just beginning to understand how exactly IF may impact the health of the gut microbiome. What is well established is the intake of fiber, and other foods that enhance gut microbes are linked to an increase in insulin sensitivity, reduced inflammation, enhanced immune tolerance, and many other health benefits. But what it also linked to these same health benefits is intermittent fasting!

I believe we have much more to learn about the link between the gut microbiome and intermittent fasting as a therapeutic tool to impact risk for chronic disease, improve health and increase longevity.

I just sat down with my long-time friend and former clinical director for the Dr. Oz show, Mike Hoaglin to talk about our shared passion for how fasting impacts the gut microbiome. He shared with me the results of a fascinating experiment he tried on himself to elucidate this relationship.

Mike currently works as the clinical lead for uBiome, a biotechnology company dedicated to helping patients and clinicians understand how the gut microbiome impacts health and disease. By submitting a stool sample, uBiome sequences your gut microflora which detects both beneficial and pathogenic microorganisms associated with inflammatory conditions like IBS, ulcerative colitis and Crohn’s Disease.

After watching the docuseries I co-hosted with Montel Williams, The Real Skinny on Fat, where we delve into the science behind why fat is actually healthy and how fasting can reduce your risk of cancers, improve your immunity, activate stem cells and enhance longevity, Mike was inspired to do his own five-day water fast and see what kind of impact it had on his microbiome. He was also curious to feel the impact on his energy levels, brain fog, and mental acuity.

He tested his microbiome using uBiome prior to the start of his fast. The results showed that he had dysbiosis — an imbalance in his gut bacteria with low biodiversity and too much of the harmful bugs (bacteria) that are known to contribute to inflammation.

Under the supervision of his functional medicine practitioner, Mike chose five days in his schedule where he could take time from work and would have the house to himself because his wife would be traveling in order to do the fast.

As typical for the first couple of days on a fast, Mike found it a challenge to go without food. He was cranky and hungry, but thankfully able to sleep. By day three his hunger subsided and he could tell that his blood sugar was low but the fast wasn’t as difficult as it was on the first two days. By day four though, his energy was starting to increase, he was more productive, had more clarity, felt lighter and could tell that his body was adapted to burning stored fat as fuel. During the docuseries, he had learned that on day four his stem cells were starting to activate. This fueled his excitement for the rest of the fast, knowing that he was activating internal anti-aging signals on the cellular level.

At 5:00 pm on day five Mike broke his fast with a cup of bone broth. Bone broth is the perfect food to transition out of a fast. It contains important amino acids like glycine and glutamine that offer nourishment to the digestive tract as it starts to process food again. Add a little bit of Himalayan salt to your bone broth for added minerals to feed your cells much-needed electrolytes. Mike continued with slow, easily digestible foods like soups and steamed veggies as he emerged out of the fast. He focused on fiber-rich plant foods to feed his microbiome, healthy fats and small amounts of slow cooked meat.

As planned, Mike tested his microbiome again after immerging from the fast. He was surprised with the results; it was as if his gut microflora had been reset by the fast. The results revealed a much more balanced profile: fasting starved out the bad bugs that were out of balance and this allowed for his ecology to gain in diversity with more of the healthy bacteria.

Since this experiment, Mike is cognizant about how food impacts his microbiome. He’s had a sweet tooth for most of his life, but eating that cookie has more meaning now, knowing the impact it can have on his microbial biodiversity, influencing it in a way that feeds the pathogenic bacteria. We spoke about how insulin gets released every time you eat a carbohydrate or protein-rich food. And how over time cells can become insensitive to insulin, leading you down the road to a whole host of metabolic and inflammatory conditions like diabetes, heart disease, and cancer. It’s not always obvious either. There’s a term called “skinny fat” where a person may look skinny on the outside but is actually storing visceral fat in the abdominal cavity, around the organs. This visceral fat has been linked to an increase in heart disease, high cholesterol, insulin resistance, and lower bone mineral density.

To get a good picture of how well your body is handling insulin, ask your doctor to get your fasting insulin tested. This, along with understanding the health of your microbiome are two of the most important indicators for health and the prevention of disease.

If you’re interested in fasting but feel intimidated, intermittent fasting may be an easy place to start. In my New York Times bestselling book, Glow15, I talk in detail about my personal experiences with, and also the established benefits of intermittent fasting. Here’s how IF works on the Glow15 plan: on three non-consecutive days, you will fast for 16 hours and eat during an eight-hour period. You can begin your fast after dinner so that the majority of your non-eating hours occur during sleep. For example, if you stop eating at 8:00 pm, and then fast overnight, your first meal will be at 12:00 pm the next day. Essentially, you will only be skipping breakfast! As long as your fast lasts for 16 hours, you can adapt your IF to your schedule. If you have any digestive issues and have tried every diet with no relief, I am so excited for you to grab your copy of Glow15. The softcover version of the book just launched, and in the book, I guide you through how to make the hours work for you, your body and your lifestyle.

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