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How to Make Fasting Easier, Safer and More Effective

Written by Dr. Joseph Mercola Fact Checked

Story at-a-glance -

  • KetoFasting combines a cyclical ketogenic diet and intermittent fasting with cyclical partial fasting to optimize health and longevity and support safe detoxification
  • The KetoFast protocol is easier to comply with than multiday water fasting, and provides greater benefits because you’re able to do it far more frequently than you could do multiday water fasting
  • Many of the benefits of fasting occur when you refeed, and this is why cycling in and out of fasting and feasting is so valuable. Half of the process occurs in the absence of food, while the other half occurs when food is reintroduced
  • One of the primary reasons for why you would want to fast is to accelerate autophagy. This is your body’s innate cleanout process, in which damaged mitochondria, proteins and cellular components are digested and then recycled during the regeneration phase, which occurs during refeeding
  • As with other types of extended fasting, you should not do KetoFasting if you are underweight, pregnant, breastfeeding or have an eating disorder

In the podcast above, Chris Kresser — an acupuncturist, licensed integrative medicine clinician and co-director of the California Center for Functional Medicine — and I talk about KetoFasting, the program I developed and detail in my latest book, "KetoFast: A Step-By-Step Guide to Timing Your Ketogenic Meals," which launches today. Within a week or two the accompanying KetoFast cookbook will also be released.

My previous book, "Fat for Fuel," released May 16, 2017, became an instant nationwide No. 1 best seller, beating out the No. 2 best-selling book by a significant margin.1

However, while The Washington Post and some others accurately listed "Fat for Fuel" as No. 1 based on Nielsen ratings for that first week,2 The New York Times (NYT) — considered the pre-eminent list of best-selling books in the U.S. since 1931 — didn't even include it in their top 15.3

Such a blatant omission is highly unusual, so Hay House, my publisher for that book, reached out to find out why the NYT censored it. The NYT replied the book was "disqualified" because too many of the sales went through Amazon. This in and of itself is unusual, considering Amazon is a primary outlet for all books.

Based on what happened with "Fat for Fuel," I expect more of the same with "KetoFast." Still, the NYT was unable to prevent "Fat for Fuel" from becoming a best-seller and fueling a keto revolution that is now the hottest lifestyle trend around, and I doubt the NYT will be able to quell the success of KetoFasting either, even if they decide to repeat their censorship.

From 'Fat for Fuel' to 'KetoFast'

There's no doubt conventional, government-approved advice has utterly failed to help people manage their weight and prevent disease. We're facing overwhelming rates of obesity, heart disease, cancer and Alzheimer's, with future projections heralding more of the same. We need a radical U-turn, and the foundations for how to accomplish that are clearly spelled out in "Fat for Fuel."

This is why I recommend you read that book first, and implement the nutritional basics of a cyclical ketogenic diet and intermittent fasting before you move on to "KetoFast." You could look at the two books as two parts of a complete lifestyle program, with "KetoFast" picking up where "Fat for Fuel" left off.

The key to weight management and optimal health is to optimize your mitochondrial function — hence, the term metabolic mitochondrial therapy (MMT) used in "Fat for Fuel." In short, if your mitochondria are not functioning properly, none of your bodily systems will function properly, and in order for your mitochondria to work, having the metabolic flexibility to burn fat is essential.

"Fat for Fuel" explains the many metabolic advantages you gain once your body regains the ability to burn fat for fuel, and details how to do it. The initial phase of the MMT program — which ends once your body is able to effectively burn fat for fuel — can take anywhere from weeks to months or longer, depending on how metabolically damaged you are.

While much of the book centers around diet (raising the amount of healthy fat and decreasing net carbs is what pushes your body into burning fat for fuel), it also reviews a variety of other strategies to improve your mitochondrial function, such as cold thermogenesis, photobiology, detox, exercise, the dangers of iron overload and the pernicious influence of electromagnetic fields (EMF).

"KetoFast" is the next phase once you've successfully implemented the MMT program, as it now combines a cyclical ketogenic diet and intermittent fasting with cyclical partial fasting.

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KetoFasting Will Amplify Benefits of My Basic MMT Program

The impetus behind "KetoFast" was two major realizations: First, that water-only fasting is a tremendously beneficial health intervention; and second, that while water-only fasting used to be an ideal strategy, the fact that in the 21st century we have increased toxic exposure that makes it potentially dangerous to do extended water fasts.

We're now surrounded by and exposed to some 80,000 chemicals in our environment, most of which are fat soluble, meaning they accumulate in your fat cells. Meanwhile, fasting effectively drives toxins out of fat cells, which can have devastating results if you're severely toxic.

What's more, since you're not eating, you're also not providing your body with the nutrients it needs to effectively neutralize and eliminate those released toxins. My answer to make fasting safer was to devise — based on the best scientific evidence I could find — a fasting program that mimics multiday water-only fasting, while supporting your detox pathways and minimizing the risks associated with toxicity.

The KetoFast protocol is also easier to comply with than multiday water fasting, and provides greater benefits because you're able to do it far more frequently than you could do multiday water fasting.

The caveat, again, is that you need to have done at least a month of daily intermittent fasting and achieved nutritional ketosis as laid out in "Fat for Fuel" before you move on to KetoFasting. Once you're metabolically flexible and can burn fat for fuel, the combination of cyclical nutritional ketosis and partial fasting can further amplify your weight loss and overall health and longevity.

Why Fast?

As mentioned in the featured interview, fasting has a wide range of health benefits, including radically improved sleep, which in turn is a crucial component of good health and longevity. When you're fasting, you'll often find you're sleeping much better, and your cognition typically improves thanks to the biological cleansing and regeneration that occurs throughout your body, including your brain.

In my view, one of the primary reasons for why you would want to fast is to accelerate autophagy. This is your body's innate cleanout process, in which damaged mitochondria, proteins and cellular components are digested and then recycled during the regeneration phase, which occurs during refeeding.

It's important to realize that many of the benefits of fasting actually occur when you start eating again, and this is why cycling in and out of fasting and feasting is so imperative. Half of the process occurs in the absence of food, while the other half occurs when food is reintroduced.

This is yet another reason why I don't recommend longer fasts, as this will prevent you from fasting often, hence limiting the number of cycles of regeneration you get.

Fasting also boosts your readiness score, which means following a fast, you're able to work out really hard. I do KetoFasting twice a week, and on the days following my KetoFast, that's when I do my strength training and load up on protein and carbs. I've found it's a really fabulous and nearly pain-free way to radically improve your metabolic health.

Other Benefits of Fasting

Fasting is also known to provide many other health benefits, including:4,5,6,7,8

Stem cell activation — Stem cells play an important role in health and longevity as they are instrumental in repairing and rejuvenating your cells and tissues. By upregulating autophagy and mitophagy (autophagy in your mitochondria) 9 and boosting stem cells you will lower your risk of most diseases, including cancer10 and neurodegeneration.11

Nutrient composition is important here, and in "KetoFast" I provide details on how to optimize autophagy and stem cell activation processes by eating certain foods (and avoiding others) at the right time.

Releasing ketones into your bloodstream, which help preserve brain function and protect against epileptic seizures, cognitive impairment12 and other neurodegenerative diseases.

Boosting brain-derived neurotrophic factor, which stimulates creation of new brain cells and triggers brain chemicals that protect against brain changes associated with Alzheimer's and Parkinson's disease.13,14

Increasing growth hormone by as much as 1,300 percent in women and 2,000 percent in men,15 thereby promoting muscle development and vitality.

Lowering insulin and improving your insulin sensitivity; studies have shown intermittent fasting can both prevent and reverse Type 2 diabetes, which is rooted in insulin resistance.16,17,18,19

Increasing levels of the neurotransmitter norepinephrine, which helps your body break down fat to be used as fuel and benefits your metabolism.20,21,22

Boosting mitochondrial energy efficiency and biosynthesis.

Lowering oxidative stress and inflammation.23

Improving circulating glucose24 and lipid levels.

Reducing blood pressure.

Improving metabolic efficiency and body composition, modulating levels of dangerous visceral fat and significantly reducing body weight in obese individuals.

Reproducing some of the cardiovascular benefits associated with exercise.

Regenerating the pancreas25 and improve pancreatic function, reversing diabetes.

Improving gut health — While the exact mechanisms are still unclear, I believe fasting helps jump-start microbiome health by increasing bacterial diversity and repairing leaky gut. Overall, fasting facilitates healing of your gastrointestinal tract and enhances the integrity of your gut lining.

Protecting against cardiovascular disease.

Reducing low-density lipoprotein and total cholesterol.

Improving immune function.26

Synchronizing your body's biological clocks.27

Eliminating sugar cravings as your body adapts to burning fat instead of sugar.

Increasing longevity — There are a number of mechanisms contributing to this effect. Normalizing insulin sensitivity is a major one, but fasting also inhibits the mTOR pathway, which plays an important part in driving the aging process.

Safety and Contraindications

For all its benefits, fasting — especially multiday water-only fasting — is not for everyone. As with other types of extended fasting, you should not do KetoFasting if you are:

  • Underweight
  • Pregnant
  • Breastfeeding
  • Have an eating disorder

This is a small minority of people, and for pregnant and breastfeeding women it's a temporary contraindication. For most others, fasting is likely to provide significant health benefits, and my KetoFast protocol raises not only your chances of fasting successfully but also improves safety, as it's designed to support detoxification.

Why I Don't Recommend Continuous Nutritional Ketosis

"Fat for Fuel" and "KetoFast" both stress the importance of a cyclical ketogenic diet. A common misconception is that because nutritional ketosis is so beneficial, it stands to reason that remaining in ketosis for the rest of your life would be the way to go. I disagree with this approach, having experienced the drawbacks of it firsthand.

For starters, continuous keto can start wreaking havoc with your hormonal system, specifically your thyroid. It's important to realize that nutritional ketosis is a catabolic process, meaning you're breaking things down. This is a good and necessary process, but you also need to build your body back up!

Many advertise the ketogenic diet as something you stay on forever, and I quickly learned that was a bad idea. After some months, you begin to lose muscle mass, for example, which is the complete opposite of what you're looking for, especially if you're older, since you will automatically lose muscle mass with age anyway.

Hence, I strongly recommend cycling in and out of ketosis once you've regained your metabolic flexibility and are able to effectively burn fat for fuel. In other words, you stay in ketosis only long enough to make sure you're burning fat, and then you move into a more balanced approach where you're adding in higher amounts of healthy carbs once or twice a week.

The Dark Side of Water-Only Fasting

I also do not recommend strict multiday water-only fasting, even though historically this has been a very successful and beneficial approach. The reason for my change in view is because our toxic exposures have dramatically increased, which makes fasting riskier now than it ever was historically.

As mentioned, fat-soluble toxins are stored in your fat cells, and when you fast and rapidly lose weight, those toxins are released, with potentially devastating effects.

Matters are made worse by the fact that many people have poorly functioning detoxification systems and simply aren't metabolically healthy enough to metabolize all those toxins. Phase 2 detox pathways in particular tend to be dysfunctional or impaired in many. Toxicity is typically the reason why people feel horrible when fasting. It's not an artifact of the fasting process in and of itself.

Another reason why I don't recommend multiday water fasting is because compliance is so poor. Naturally, if you cannot comply with the program, you cannot reap the benefits. Many would rather lose a foot than go without food for five to seven days straight. My KetoFasting protocol is a pragmatic approach designed to optimize compliance.

Lastly, when you're doing multiday water fasting, you're really limited in how many times a year you can do it. If you did it once a month, which would be rare, you'd still only cycle through the regeneration process just 12 times in a year. If you fast once a quarter, you're down to four times a year. You also have to refeed more cautiously after going without food for several days.

With KetoFasting you can cycle through the regeneration process anywhere from 52 to 104 times a year, and you can jump right into feasting, eating lots of protein and carbs the day you break your fast.

KetoFasting Defined

I do not think it is wise to jump into KetoFasting without doing the preliminary work detailed in "Fat for Fuel." You really need to be metabolically flexible and able to burn fat for fuel before you start KetoFasting. At bare minimum, you should not skip step No. 1 (below). That said, the following is a three-step summary of my KetoFast protocol.

1. Introduction — The first step is to compress your daily eating window to six to eight hours for at least four weeks, meaning you eat all of your calories for the day during those six to eight hours, and for the remaining 16 to 18 hours, you're fasting. Also, be sure to eat your last meal at least three hours before bedtime to avoid creating unnecessary free radicals.

I recommend testing your ketones to confirm that you are in ketosis (which means your body is burning fat), especially if you are heavy to start with, or diabetic, as it might take you longer to shift. Ketocoachx.com is the best blood ketone meter out there and only costs 70 cents per strip. It is a brand-new meter that became available at the end of April 2019.

2. KetoFast days — Once you've restored your metabolic flexibility to burn fat for fuel you can move into the second phase, which involves having a single 300 to 500-calorie meal, ideally breakfast, followed by a 24-hour, water-only fast, once or twice a week.

To determine how many calories you should have at this meal, first calculate your lean body mass by subtracting your percent body fat from 100. (So, if you have 20% body fat, you have 80% lean body mass.)

Multiply that percentage (in this case, 0.8) by your current total body weight to get your lean body mass in pounds. Next, multiply your lean body mass in pounds by 3.5. This is the number of calories you'll want to eat for that meal. The following is a general guide for the nutrient ratios you're looking for in this meal:

Carbs — Less than 10 grams of net carbohydrates (total carbs minus fiber) so as not to replete your glycogen stores. Primarily, your carbs would then be nonstarchy vegetables, seeds or nuts.

Protein — Half of your personalized daily protein requirement, with a focus on plant based protein, not animal protein. If you're younger than 60, a general recommendation for your daily protein requirement would be 0.8 grams of protein per kilogram of lean body mass, or 0.5 grams of protein per pound of lean body mass.

Let's say your daily protein requirement is 80 grams. For this meal, you'd cut that in half to 40 grams. The key here is not just lowering your overall protein intake, though; rather, it's restricting branched-chain amino acids (such as leucine, for example), found primarily in meat and dairy products.

The reason you want to restrict branched-chain amino acids at this meal is because they inhibit autophagy — essentially blocking the very cleanout process you're trying to activate through fasting. Aside from plant-based protein, an ideal form of protein to include in this meal is collagen and/or bone broth, which provide great support for your connective tissue without inhibiting autophagy. Chlorella is another excellent protein you can include.

Fat — The remainder of your calories comes from healthy fats such as coconut oil, avocado, MCT oil, butter, olive oil and raw nuts.

By eating just that one 300- to 500-calorie meal and then fasting for 24 hours, you essentially end up having eaten once in 42 hours. This will effectively allow your body to deplete the glycogen stores in your liver, which sends autophagy soaring.

On your KetoFast days, you also need to avoid any supplements you might normally take that will inhibit autophagy. Commonly used supplements that should be avoided for this reason include methylfolate, vitamin B12, exogenous ketones, colostrum and glutamine.

Supplements that support autophagy that you can take during your KetoFast include berberine, ECGC, pomegranate peel extract or powder and organic chamomile tea, as these activate autophagy and will support the process.

3. Refeed day — After completing your 42-hour KetoFast, it's time to feast. This is also the perfect time to do hardcore strength training and load up on animal protein such as grass fed organic steak and/or whey protein, as now you're in rebuilding mode, which includes muscle building.

You can also kick your carbs up to 100 or 150 grams. An ideal sequence for this day is to do your strength training in a fasted state, then have a big meal afterward. Now's also the best time to use your sauna (see below).

As for the number of meals on refeed day, I keep it consistent with my normal intermittent fasting schedule. I simply eat more at each meal. So, for example, instead of having two eggs on my salad, I'll have three on refeed day; instead of having vegan protein in my smoothie, I'll switch over to organic grass fed whey concentrate.

Tips and Tricks

In the featured interview, I also discuss tips and tricks to get you through some of the more common issues people complain about when fasting or going on a cyclical ketogenic diet. Here's a quick summary of some of the key points:

Cravings — Many struggle with hunger when fasting, but one of the beautiful benefits of intermittent fasting is that once you're able to burn fat for fuel, hunger and carb cravings vanish, since at that point your body is able to access your fat stores and create energy out of your body fat.

This is one of the reasons why you'll want to do intermittent fasting for at least a month and make sure you're in nutritional ketosis before you start KetoFasting. When you are insulin resistant, your body is not able to access and convert body fat to energy in an efficient manner, hence carb cravings and hunger pangs are the norm among sugar-burners.

Sauna — Aside from a cyclical ketogenic diet, intermittent fasting and cyclical partial fasting (KetoFasting), another key strategy that can help optimize your health span are sauna bathing and thermogenesis, or the cycling between hot and cold exposures.

I specifically recommend using an EMF-free near-infrared sauna for general health optimization but especially when KetoFasting to help with detoxification.

I recommend using your sauna daily but especially the morning after your KetoFast, as at this time your body will be releasing a significant amount of toxins. If you're strength training, consider taking a sauna directly after, and then break your fast with a high-protein meal that has plenty of branched chain amino acids and fresh fruit to stimulate mTOR.