Intermittent Fasting and Gut Health: the Science that makes it work!

Intermittent Fasting and Gut Health: the Science that makes it work!

Intermittent Fasting is just about NOT EATING FOOD, right? So why would anyone want to understand the science of how and why it works…?

In this post, I’ll do my best to make this complex topic easier to understand. My hope is that if the science behind Intermittent fasting makes sense – it will be easier to begin and follow a fasting program as a way to improve your health.

Fasting can help you feel better, lose weight, reduce your risk of disease, and increase your longevity. These health benefits are due, in large part, to the fact that Intermittent Fasting improves your Gut health!

Let’s start with an overview.

First we need to explain the difference between an “Eating state” and a “Fasting state“:

  • An Eating state begins when you start to eat a meal, and lasts somewhere between 3 to 5 hours after a meal is completed, while your body digests and absorbs the food you have just eaten.
  • In this Eating state, your body is burning glucose from digesting carbs and proteins, and your insulin levels stay high.
  • After the “Eating” state ends, your body goes into an Intermediate phase, called the “Post-absorptive” state.
  • The Post-absorptive state will end somewhere 8 -12 hours after your last meal.
  • It’s only after the “Post-absorptive” phase has ended that your body enters into a true “Fasting” state.
  • Because the Fasting state does not actually occur until roughly 12 hours after your last meal it is rare for people who eat multiple small meals, for people who snack frequently, or for those who eat over the course of many hours of the day to ever get into an actual Fasting phase.
  • This is important because it’s only when you are in the Fasting state, that your body changes its metabolism, shifting to burning FAT for fuel, instead of carbs and proteins.
  • Because of this shift, your body does not need to produce insulin and as a result, your insulin levels remain low during this metabolic shift. (From The Beginners Guide to Intermittent Fasting“, by James Clear.) (3)

Summary – 3 States of Fasting:

EATING state. Burning glucose from carbs and protein, insulin, and blood sugars are high. Lasts for 3-5 hours after eating.

INTERMEDIATE/ Post-absorptive state. Lasts for 8-12 hours after the Eating State is complete.

FASTING state. Burning fat for fuel. Lasts until the next meal. Insulin levels remain low, blood sugar remains low.

The Science of Intermittent Fasting

Researchers have defined three specific ways that Fasting provides health benefits:

1. Stimulating Autophagy

2. Inhibiting mTOR Pathway

3. Inducing Ketosis

Dr. B.J. Hardick writes frequently about the health benefits of fasting. In his recent article from May 2018, he discusses the science behind fasting. “Health Benefits of Fasting: mTOR Pathway, Autophagy & Ketosis” (5)

In this article, Dr. Hardick argues that reducing your caloric intake by 20-40% is the most effective way to regulate aging and increase a healthy lifespan. Fasting is an easy way to get the benefits of this technique of calorie reduction – without the fuss of calorie counting or measuring.

(1) Autophagy

“Autophagy” is the process of Spring Cleaning your cells, and it is the body’s way of recycling and removing unnecessary debris.

Cleaning up that cellular junk relieves cells from various stress conditions. Autophagy also contributes to cellular development and differentiation, suppresses tumors, and supports immunity by (among other ways) blocking invading pathogens. These and other actions improve your cells – and therefore your lifespan.

“Eating shuts down Autophagy… the greater the amount of time each day that you eat, the less of an amount of time Autophagy (cleaning) occurs.”

Dr. B.J.Hardick

(2) mTOR Pathway

The mTOR Pathway is a process that involves enzymes and that keeps your cellular machinery running smoothly: generating energy and managing cell growth, protein synthesis, and autophagy. As a result, the mTOR pathway is an important part of sensing nutrient availability.

“When we eat carbohydrates or protein, insulin is secreted, and the increased insulin levels, or even just the amino acids from the breakdown of ingested protein, activate the mTOR pathway. The body senses that food is available and decides that since there’s plenty of energy to go around, there’s no need to eliminate the old sub-cellular machinery.”

“There is a balance here, of course. You get sick from too much Autophagy as well as too little. Which gets us back to the natural cycle of life – feast and fast. Not constant dieting. This allows for cell growth during eating, and cellular cleansing during fasting. Balance. Life is all about balance.”

Dr. Hardick also references work by Dr. Jason Fung’s, The Complete Guide to Fasting. (6)

“You want Autophagy and mTOR to occur in the right balance. Too much or too little of either can create problems. A key way to establish and maintain this balance is through Fasting combined with Ketosis.”

Dr. B.J. Hardick (5)

(3) Ketosis

Ketosis is one notable factor that many rely heavily on when intentionally fasting. When the body believes food sources are scarce, it turns to stores of fat for its energy, rather than using muscle and circulating carbohydrates. When the fat begins to release and burn (a process called ketogenesis), chemical byproducts called ketones are released into the urine.

For those pursuing Intermittent fasting for specific health goals, particularly weight loss, ketogenesis is often a goal. Some go as far as measuring the ketones in their urine daily with an at-home test strip. It should be noted that ketogenesis is not always considered a positive effect. For diabetics, for example, a state of ketosis is a dire one, and medical help should be accessed immediately.

“Simply put, Ketosis occurs when your body utilizes FAT – more specifically as your body metabolizes ketones, the result of fat metabolism, rather than glucose (from carbohydrates) as its primary fuel. Notice I said fat. A diet high in fat is one way to get into Ketosis. Fasting is another way because your body draws on stored fat for fuel.

Therefore, from an evolutionary perspective, this makes sense. Think about what happens when you fast for, say, 24 hours. Today you do this out of choice, but in our hunter-gatherer days, you might not have any available food coming in some days.

I’ve talked elsewhere about a ketogenic diet’s other health benefits and potential drawbacks, but here let’s focus on aging and longevity. Researchers believe ketosis can benefit neurodegenerative disorders including Alzheimer’s disease and Parkinson’s disease.”

Quote from Dr. B.J. Hardick. (5)

Fasting vs. Counting Calories

Fasting is a way to get the benefits of Ketosis without needing to be hyper-vigilant about counting calories. You can determine your own program by finding a cycle that works best for you, and then focus your energies on following a healthy diet during your eating hours.

The Gut health benefits of incorporating fasting into your lifestyle are remarkable! And, in addition, you may discover that fasting also improves your energy, digestion, sleep, and mood – but it also is surprisingly easy to add to your lifestyle!

“Fasting has been practiced for millennia, but only recently studies have shed light on its role in adaptive cellular responses that reduce oxidative damage and inflammation, optimize energy metabolism, and bolster cellular protection.

... Regular fasting extends longevity in part by reprogramming metabolic and stress resistance pathways.

In rodents, intermittent or periodic fasting protects against diabetes, cancers, heart disease, and neurodegeneration, while in humans it helps reduce obesity, hypertension, asthma, and rheumatoid arthritis.

This research indicates that “fasting has the potential to delay aging and help prevent and treat diseases while minimizing the side effects caused by chronic dietary interventions.”

US Library of Medicine – Abstract. “Fasting: Molecular Mechanisms and Clinical Applications”, V. Longo and M. Mattson (2)

In Conclusion:

  • Fasting can help to heal your gut by improving the gut barrier and reducing gut permeability.  These improvements help to repair a condition known as “leaky gut” syndrome.  This condition is considered by many practitioners to be the precursor to autoimmune disease (along with many other modern health conditions).
  • “Researchers find that beyond its benefits on your body and brain, Intermittent fasting could favorably influence the balance of beneficial gut flora that protects against metabolic syndrome, a traffic jam of issues that include high blood sugar and abdominal obesity.” He continues, “Losing weight reduces inflammation and can improve gut ecology.” Dr. Vincent Pedre:
  • Dr. Pedre argues, “You win on every level: You look and feel better. Gut health improves. And lower inflammation scores reduce your risk for nearly every disease.” (How to Heal Your Gut With Intermittent Fasting –

Important Disclaimer: Fasting is not for everyone. If you are pregnant, nursing, have a history of eating disorders, are on medication to regulate blood sugar, or are under the care of a doctor, you should check with your physician first before starting any fasting protocol.

Peg Desrochers

True Gut Health

Live a Vibrant Life!

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