Why I settled on Three Days for Cancer-Prevention Fasts

Intermittent fasting and time-restricted eating have been a huge part of my health journey and of Lisa’s, thanks to an introduction to the concept from Dr. Jason Fung.

When we tried 10 weeks of alternate-daily fasting, that was when Lisa really started to see impressive weight-loss results.

Now fasting is just part of our routine. As I’ve tracked with the Zero app, I have fasted at least 13 hours on 269 of the last 270 days.

Usually I have two meals a day, four to eight hours apart. Sometimes it’s just a single meal, a.k.a. One Meal A Day or OMAD, which is what Lisa typically does.

Occasionally we fast for more than 24 hours to accelerate autophagy and for cancer prevention.

I believe I first heard of the idea of fasting for cancer prevention through Dr. Fung, primarily in the context of how long-term caloric restriction has been demonstrated to increase longevity and to reduce cancer incidence, both in animals and in people.

But who wants to live like that all the time?

What if you can get most of the benefits of chronic restriction through periodic pulses of fasting, while eating normally the rest of the time?

That leaves the question of dosage: how long does the fast need to be, and how frequently do you need to do it?

The short answer is no one really knows, but here is why Lisa and I have settled on three days once a month.

I had heard about Dr. Peter Attia’s practice of a seven-day water-only fast (a.k.a. the Nothingburger) once per quarter as a potential cancer-prevention strategy, and so I decided to try a seriously extended fast for the first time about 15 months ago.

Instead of water only I also allowed myself coffee, and I went five days, from Sunday evening to Friday evening. I did another of these last February, but cut it to four days because my sleep quality the previous night hadn’t been good.

Meanwhile I heard that Dr. Attia had changed his personal practice to a three-day fast each month. It’s two more days of fasting per quarter, but spread out over three months instead of all at once.

As I said, no one knows the “right” dose and frequency, but this seemed like something worth trying.

In November and December I did three-day fasts. The slightly lower intensity than my previous 4-5 day fasts was appealing, but I still had that nagging question of whether it was enough.

Then I finally checked out some videos from Professor Thomas Seyfried (as highlighted in my last post) on the metabolic approach to cancer treatment through a ketogenic diet and related interventions.

He described the glucose-ketone index (GKI) he had developed to measure whether patients were in an optimal, deep level of ketosis. A GKI of 9.0 or less indicates some level of ketosis, with 1.0 or lower being the highest therapeutic level.

Increasing ketones and reducing glucose allows normal cells to thrive, while cancer cells – which lack the ability to use ketones for energy – are placed under stress.

I also was interested in confirming that my normal blood sugar levels weren’t masking an underlying condition called insulin resistance. If I had normal blood sugar levels only because my pancreas was cranking out lots of insulin, that would not be healthy.

I felt pretty confident that I had reversed any insulin resistance I may have had before my weight loss, but I wanted to confirm it.

Testing insulin levels is complicated and expensive, but I had learned that having ketone readings of 0.5 mmol/L or higher is a back-door way of confirming low insulin levels. They’re in a reciprocal relationship: elevated ketones aren’t compatible with high insulin.

I also heard someone mention the Keto-Mojo device that enables home measurement of blood glucose and ketones, and which enables tracking through a mobile app, so I took the plunge and got a starter kit for about $100.

My Keto-Mojo arrived the day after I started my December fast, and that evening my GKI was 3.2. By the 48-hour mark of my fast I reached 1.0 and I stayed below that (0.8, 0.5 and 0.5) until I broke my fast 24 hours later. I remained below 3.0, which is considered high-level ketosis, for another 24 hours. I maxed out at 6.2 mmol ketones with blood sugar at 61 mg/dL.

It seems that if GKI at or below 1.0 is the therapeutic target for those undergoing metabolic cancer treatment, being there for at least 24 hours once a month gives a reasonable chance of being helpful in cancer prevention.

It isn’t rock-solid confirmation for the three-day fast Dr. Attia uses, but it gives me some reason to believe I’m in a fasting range that should be beneficial.

I think Professor Seyfried put it well toward the end of the video I embedded in my last post:

These are non-toxic approaches. I can’t tell you whether it’s going to be the solution to the cancer problem. But I can tell you ‘I think it works, and it’s not going to hurt you. And it has the potential mechanistically to be very effective.'”

Thomas Seyfried, Ph.D.

Our next three-day fast starts tomorrow afternoon. This time I’ll be working to ensure I’m in ketosis before I start my fast, which should make it easier, and also will be taking GKI readings throughout the full fast instead of starting partway through the fast.

I’ll also explore strategies to get to that GKI ≤ 1.0 as quickly as possible to have the greatest therapeutic effect.

I’m not asking you to join Lisa and me in this fast, but if you’re curious I do invite you to follow along as I share observations on Facebook, Twitter and LinkedIn.

I’ll also write a daily recap post here that you can receive if you subscribe by email.

Check out My Health Journey for the full story of our health improvements, and my #BodyBabySteps for an approach to how I would do it if I were starting today, based on what I’ve learned.

Fasting for Cancer Prevention

While extended fasting can have a broad range of benefits, the real reason for my monthly three-day fast is for cancer prevention.

Professor Thomas Seyfried of Boston College, one of my Health Sherpas, has pioneered research that has significantly challenged the somatic mutation theory of cancer, which holds that cancer results from an accumulation of random DNA mutations in the nuclei of cells, which cause them to grow out of control.

Seyfried has championed a metabolic theory of cancer, which essentially says that cancer results from damaged mitochondria, the power plants of the cell.

The video below, in which he addresses a lay audience, provides a compelling presentation of his case.

He first dismantles the somatic mutation theory by showing how it is incompatible with the results of several studies.

He then convincingly describes the metabolic theory of cancer and how it better fits the data, explaining how cancer cells can have so many different mutations in the nuclear DNA, and yet have so many features in common.

The damaged mitochondria generate reactive oxygen species (ROS) that cause the DNA mutations in the cell nucleus. Those mutations are downstream from the real cause of cancers.

This video from last September is more technical, but also includes some updates on applications of his theory in cancer treatment. It’s worth watching if you want a deeper investigation.

Watch the video below first for an introduction, and afterwards scroll down and I’ll describe why I see a monthly three-day fast as a valuable cancer-prevention strategy.

You did watch it, right?

If not, hit the play button and read on when you’re done.

As Professor Seyfried explains, cancer cells use fermentation of sugar to generate energy, and lack the flexibility to use oxygen and ketones because of damaged mitochondrial structures.

As I mentioned previously, one of the benefits of fasting is autophagy, which causes cellular cleanup and recycling of defective organelles like the mitochondria. So one cancer-prevention mechanism is replacing mitochondria that are throwing off ROS and causing mutations with new and improved versions.

The second mechanism is by introducing ketosis at a level that is far beyond a typical ketogenic diet. We all have lots of cancer cells in our bodies at any given time, and our immune system kills off many of them.

But as Professor Seyfried says, cancer cells have lost the metabolic flexibility to use ketones for energy because of their damaged mitochondria. An extended fast drives ketone levels high enough to cause the remaining cancer cells to die, or at least slows their ability to grow and proliferate.

Ketones and blood sugar are inversely related. As blood sugar goes down due to caloric restriction (or a fast), ketone levels go up. And as glucose goes up, tumor size increases.

“It doesn’t mean that sugar causes the cancer, but if you have the tumor, the tumor will grow faster with the higher blood sugar.”

Professor Thomas Seyfried

Later in the video, in the Q&A session, Professor Seyfried describes meeting members of the Calorie Restriction Society of America, people who severely and continuously limit their food intake, and how they have virtually zero incidence of cancer.

He also suggests that long-term caloric restriction is no way to live.

I agree with that.

I see periodic episodes of extended fasting as a way of getting most of the benefits of long-term caloric restriction without the soul-crushing grind of continual deprivation.

As I said in my last post, no one really knows how long is long enough for these extended fasts, or how frequently they should be done.

In my next post I’ll describe why I’ve settled on a three-day fast once a month as my dosage, with a low-carb, high fat (LCHF) lifestyle and time-restricted feeding as the foundation.

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Why do a three-day fast?

I’m not suggesting you should do an extended fast. In fact, I wouldn’t recommend it until you have:

  1. Become fat-adapted through at least four weeks of a low-carb, high-fat ketogenic diet, and
  2. Become comfortable with time-restricted feeding, with several weeks of maintaining fasting windows of 18-24 hours.

Doing #1 makes #2 much easier, but don’t rush it. Focus on eating your satisfying low-carb meals when you feel hungry, and start by avoiding post-dinner snacks.

Your goal is to achieve metabolic health, not to demonstrate willpower.

But once you feel established in a ketogenic eating pattern and have done some alternate-day fasting, extended fasts can create some impressive metabolic health benefits by unleashing autophagy.

Autophagy literally means “self-eating.” When nutrients are scarce, your body goes into this clean-up mode in which it digests and recycles cellular parts that are weak or defective, and replaces them with newly generated ones. See an excellent explanation of autophagy by one of my Health Sherpas, Dr. Jason Fung.

For a compelling overview of the benefits of autophagy, here’s a helpful video from another of my Sherpas, Dr. Sten Ekberg:

If you didn’t watch the video, the benefits Dr. Ekberg cited included:

  • Anti-aging – caloric restriction has been shown to improve lifespan, and many of these same benefits are thought to result from periodic extended fasting.
  • Detoxification as damaged proteins are recycled
  • Immune system enhancement
  • Improved tissue quality
  • Lowered insulin levels and increases in growth hormone
  • Reducing skin sag with weight loss, as the extra skin is broken down and recycled.
  • Brain-related benefits ranging from traumatic brain injury recovery to symptom improvement in Alzheimer’s and Parkinson’s diseases.

Even a relatively brief period of fasting triggers autophagy at some level, but to significantly activate it likely takes a couple of days or more. But unlike ketosis, which can be detected with a simple breath or finger-stick blood test, demonstrating autophagy requires a muscle biopsy.

Still, I think the framework Dr. Ekberg suggests is likely accurate: if you’re eating the Standard American Diet (SAD), you’ll likely take 72 hours or so for meaningful autophagy, but if you’re already fat-adapted it happens much sooner.

So I think given the eating pattern Lisa and I have been observing for more than a year, we’re likely getting a dose of autophagy with our 18-24 hour fasts.

One of the most compelling implications of autophagy is in cancer prevention, but no one really knows yet how large the dose needs to be.

This has been an topic of significant research interest and speculation that I will discuss in my next post.

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Check out My Health Journey for the full story of our health improvements, and my #BodyBabySteps for an approach to how I would do it if I were starting today, based on what I’ve learned.

The Fast after the Feast

Some people I respect recommend doing an extended fast before holiday feasts. Dr. Peter Attia, one of my Health Sherpas and the medical director for the Zero fasting app, often leads a group fast before Thanksgiving and Christmas.

This is a good approach because it allows you to enjoy holiday feasts guilt-free: you’ve already paid your dues.

For Lisa and me, with our wedding anniversary on Dec. 22, that’s not such a good option. We did our feasting from then through Dec. 26, and I began my extended fast at 5:30 p.m. on Sunday, Dec. 27.

During our feasting period, I had gained 7.4 pounds. And to be candid, I had already crept up a couple of pounds in the first half of the month. So by the day after Christmas I was 10 pounds heavier than my November average.

Clearly this was a lot of water weight based on my high carbohydrate intake. I also felt more stiff, with some carb-based inflammation.

The goal of my fast was to burn through that carb excess quickly to get into fat-burning mode, and so to jump-start the process I began early Monday morning with a high-intensity interval training workout, as Dr. Attia advises.

My Tuesday workout included free weights and a zone 2 cardio workout. This lower-intensity training is at the maximum level of exertion that can be sustained without burning glucose. That’s both necessary, because glycogen stores are depleted by the second day of a fast, and desirable, because it improves the muscles’ ability to burn fat.

Wednesday I did another zone 2 workout for the same reasons.

I had set on my Zero app timer goal at 36 hours, but my real goal was a three-day fast. I wanted to be able to declare victory early in case I wasn’t feeling well. I was able to finish strong, however, and had my fastbreaker just after 6 p.m. Wednesday.

It’s important to not overeat coming out of an extended fast of more than 48 hours, and particularly to not overdo carbs, which cause you to retain water and can throw your electrolytes out of balance.

My keto-friendly first meal is below, although I’ll confess that I did go back for one more stuffed pepper. The graph at right shows results of my morning weigh-ins for December and into today, which was my 300th consecutive day using our Bluetooth scale.

Why the 2.6-pound bump at the end? Last night was New Year’s Eve.

I guess I feasted before and after the fast.

I’ve done several of these longer fasts in the last year. One was five days and another four, and my plan going forward is to do a three-day water-only (or water and black coffee) fast once a month.

I’ll discuss reasons behind this in my next post, along with some interesting findings from the glucose/ketone meter I used for the first time this week.

If you haven’t tried fasting or time-restricted eating, you can take a great first step toward improving your health and vitality as we start 2021 by just not eating in the evenings.

I’m not suggesting some grand New Year’s Resolution that sets you up for failure. Just some #BodyBabySteps.

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Holiday Feasting is Fine

To lose more than 50 pounds each, Lisa and I have adopted a low-carbohydrate, high-fat (LCHF) ketogenic pattern of eating, combined with periods of time-restricted eating or intermittent fasting (IF).

We find LCHF and IF are mutually supportive. Seeking satiety in filling fats means we don’t have carb cravings, which makes it easier to go 16 hours or more without eating, also called a 16:8 fast. We almost always skip breakfast and restrict our eating to an 8-hour window, and frequently that window is even narrower.

Sometimes it’s 18:6 or 20:4, or one meal a day (also called OMAD).

It’s a lifestyle, not a diet. It’s a different pattern of eating. I fully expect we will follow it for the overwhelming majority of the rest of our days.

But as I said in my Top 20 weight loss and health tips post, “Avoidance isn’t always.” We’re in this for the long haul, and we have found that it’s a lot easier psychologically (and accords with millennia of human cultural practices) to enjoy times of feasting that we balance with extended fasting.

Rarely doesn’t mean never.

Some LCHF proponents who I deeply respect take a different view, believing that a massive infusion could be the trigger for those with carb addiction to have a relapse. And as you’re just starting out, I would err on the side of caution until you feel confident you’re well established.

But I would argue that it’s much better to have planned times of carbohydrate excess than to snitch the grandchildren’s french fries as you’ve taken them past the restaurant drive-through window.

You’re in control. You’re deciding ahead of time that for a certain period you will enjoy foods that otherwise would be off limits.

Lisa and I have just come through five wonderful days of feasting.

We celebrated our wedding anniversary, Dec. 22, by having our OMAD be pizza. Lotta carbs.

We enjoyed it so much, we did the same thing on Dec. 23. Note that the pizza shown at right is just for me. It’s gluten-free since I have celiac disease.

And yet because I hadn’t eaten for more than 21 hours, I still had an extended period of low blood sugar and insulin levels.

I also had lefse, a Norwegian potato-based treat with butter and sugar that my dad makes during the holidays. He’s developed a gluten-free version.

Three layers of awesome: gluten-free Oreos, vanilla ice cream and fudge.

From Christmas Eve until Dec. 26, we had small gatherings with my parents and then with some of our descendants that featured high-carb favorites like a traditional family potato dish, tortilla chips with queso, and my favorite frozen dessert.

With the feasting over, it was time for a compensatory fast. But instead of going straight from a high-carb state to an extended fast, I had my last meal be my four eggs/steak/cream cheese/guacamole masterpiece, and I started my Zero fasting app timer at 5:30 p.m. Sunday, with a goal of going at least 36 hours.

Lisa instead opted for a pair of consecutive 24-hour fasts. We limited ourselves to water and mineral water and black coffee, as well as magnesium supplements and some extra salt to maintain electrolyte balances.

How did it go?

I’ll share the results and my reflections on the experience in my New Year’s Day post.

If you think your friends might find this post helpful, I hope you’ll share by email or on your social networks using the buttons below.

To get these updates on a regular basis you can subscribe by email, or follow me on FacebookTwitter and LinkedIn, where I’ll also be posting links.

Check out My Health Journey for the full story of our health improvements, and my #BodyBabySteps for an approach to how I would do it if I were starting today, based on what I’ve learned.