Review: The Complete Guide To Fasting

      88 Comments on Review: The Complete Guide To Fasting

Last week, some local hospital sponsored a health fair where I work.  Employees who wanted the free cholesterol test were told to fast overnight.  At an early afternoon meeting later that day, one of my co-workers struggled to explain something, then apologized with “Sorry, I can’t think straight.  I haven’t eaten since last night, and I haven’t had time to grab lunch yet.”

Heh-heh … I hadn’t eaten since dinner the previous night either, and wasn’t planning to eat until 7:00 p.m. or so.  I wasn’t hungry, or tired, or mentally foggy.  That’s because I’m used to it.  Most Mondays and Thursdays, I don’t eat until dinner.  Those are my 24-hour intermittent fasts.

If you haven’t tried intermittent fasting, I’d recommend it.  I’d also recommend you educate yourself first by picking up a copy of The Complete Guide to Fasting by Dr. Jason Fung and Jimmy Moore.  (Why the heck this thing isn’t called Fasting Clarity is beyond me.  I’ll ask Jimmy when he visits us for Thanksgiving week.)

Dr. Fung wrote about the benefits of fasting at the end of his excellent book The Obesity Code.  This book is the extended version of those chapters, with an introduction by Jimmy, fasting success stories supplied by some of Dr. Fung’s patients, and commentary by health experts such as Mark Sisson, Abel James, Dr. Thomas Seyfried and Robb Wolf.

In his half of the introduction, Dr. Fung explains that he looked into fasting largely out of frustration.  He was treating type 2 diabetics the traditional way, and neither he nor his patients were happy with the results:

Instinctively, most patients knew what we were doing was wrong. They would say to me, “Doctor, you have always told me that weight loss is critical in the treatment of type 2 diabetes, yet you have prescribed me insulin, which has made me gain so much weight. How is that good for me?” I never had a good answer for this. Now I knew why. They were absolutely right; it wasn’t good for them.

As patients took insulin, they gained weight, and when they did, their type 2 diabetes got worse, demanding more insulin. And the cycle repeated: they took more insulin, they gained more weight, and as they gained more weight, they needed more insulin. It was a classic vicious cycle.

We doctors had been treating type 2 diabetes exactly wrong. With the proper treatment, it is a curable disease. Type 2 diabetes, like obesity, is a disease of too much insulin. The treatment is to lower insulin, not raise it. We were making things worse. We were fighting the fire with gasoline. I needed to help my obesity and type 2 diabetes patients lower their insulin levels, but what was the best approach?

Certainly, there are no medications that do this. There are surgical options that help, such as bariatric surgery (commonly called “stomach stapling”), but they are highly invasive and have many irreversible side effects. The only feasible treatment left was dietary: reducing insulin levels by changing eating habits.

The change in eating habits included adding various fasting protocols to a better overall diet.  As Dr. Fung emphasizes in the book, intermittent fasting does not give us license to live on a junk diet on non-fasting days.

Jimmy’s half of the introduction describes his own experiences with fasting, ranging from his first attempts at intermittent fasting, all the way through his n=1 experiments with 21-days fasts.  He learned a few hard lessons along the way, such as don’t drink diet sodas while fasting, and don’t try to fast when you’re in a period of high stress.

The chapters in Part One describe what fasting is and why it’s good for your health.  Part of understanding what fasting is understanding what it isn’t:  it’s not starvation, and it’s not living on a permanent low-calorie diet.

Starving and fasting should never be confused with each other, and the terms should never be used interchangeably. Fasting and starving live on opposite sides of the world. It is the difference between recreational running and running because a lion is chasing you. Starvation is forced upon you by outside forces. Fasting, on the other hand, may be done for any period of time, from a few hours to months on end. You may begin a fast at any time of your choosing, and you may end a fast at will, too. You can start or stop a fast for any reason, or for no reason at all.

As later chapters explain more fully, low-calorie diets and fasting produce markedly different hormonal responses.  That’s why most low-calorie diets fail.  We’re eating less, but still eating.  The body still believes it’s supposed to store calories, but there are fewer of them.  So the body may respond by slowing the metabolism.  Fasting, on the other hand, produces hormones that tell the body it’s time to tap the reserves.

A decreased insulin level is one of the most consistent hormonal effects of fasting. All foods raise insulin to some degree. Refined carbohydrates tend to raise insulin the most and fatty foods the least, but insulin still goes up in both cases. Therefore, the most effective method of reducing insulin is to avoid all foods altogether. During the initial stages of fasting, insulin and blood glucose levels fall but remain in the normal range, maintained by the breakdown of glycogen as well as gluconeogenesis. After glycogen is used up, the body begins to switch over to burning fat for energy. Longer-duration fasts reduce insulin more dramatically. Regularly lowering insulin levels leads to improved insulin sensitivity—your body becomes more responsive to insulin.

And later in the book …

Most people expect that a period of fasting will leave them feeling tired and drained of energy. However, the vast majority of people experience the exact opposite: they feel energized and revitalized during fasting. Partly this is because the body is still being fueled—it’s just getting energy from burning fat rather than burning food. But it’s also because adrenaline is used to release stored glycogen and to facilitate fat-burning, even if blood sugar is high. The increased adrenaline levels invigorate us and stimulate the metabolism. In fact, studies show that after a four-day fast, resting energy expenditure increased by 12 percent. Rather than slowing the metabolism, fasting revs it up.

My hesitation about intermittent fasting (before I read more on the subject and tried it for myself) centered around the belief that I’d lose muscle mass.  In a chapter titled Busting The Myths of Fasting, the book explains why that belief is wrong.  Unlike low-calorie dieting, fasting actually encourages muscle growth by spurring production of growth hormone – which makes perfect sense if you think about it from a paleo perspective.  If an unsuccessful hunt left paleo man weak and slow, he’d be even less likely to bring down prey on the next attempt.  As the book explains:

The most potent natural stimulus to growth hormone secretion is fasting. In one study, over a five-day fasting period, growth hormone secretion more than doubled. During fasting, in addition to the usual early-morning spike of growth hormone (pulsatile), there is also regular secretion throughout the day (non-pulsatile). Both pulsatile and non-pulsatile release of growth hormone is increased during fasting. Interestingly, very low-calorie diets are not able to provoke the same growth hormone response.  A study of a religious forty-day fast found that baseline growth hormone levels increased from 0.73 ng/mL to peak at 9.86 ng/mL. That is a 1250 percent increase in growth hormone, all done without drugs. And a 1992 study showed a fivefold increase in growth hormone in response to a two-day fast.

Of course, as many of us have learned from experience, fasting is much easier if your daily diet is a good one.  That means real food with real fats.  The book takes some well-deserved shots at the U.S. Dietary Guidelines, which turned us into a nation of carbivores who are hungry six times per day.  But Dr. Fung (I’m assuming this came from him) doesn’t push a strict low-carb diet either:

Relying on macronutrient-based guidelines or calorie limits makes eating far more complicated than it should be. We do not eat a specific percentage of fats, protein, and carbohydrates. We eat foods. Certain foods are more fattening than others. Therefore, the best advice focuses on eating or not eating specific foods, not specific nutrients.

There is nothing inherently unhealthy about carbohydrate-containing foods. The problem arises when we start changing these foods from their natural state and then consuming them in large amounts. The same also applies to processed fats. Processing transforms relatively innocuous vegetable oils into fats that contain trans fats, toxins whose dangers have now been well recognized.

Chapter four summarizes the many advantages of fasting: it’s convenient, it’s free and it’s flexible – you can add fasting to your lifestyle whether you’re a vegan or a confirmed carnivore.  Fasting also allows many people to free themselves of fearing every little treat:

Now, I am not saying that you should eat dessert every single day. However, fasting restores the ability to occasionally enjoy that dessert by balancing out the feast. It is, after all, the cycle of life. Feasts follow fasts. Fasts follow feasts. This is how we have always lived. Birthdays, weddings, holidays, and other special occasions have always, throughout human history, been celebrated with feasts. But those feasts should be followed by fasts.

Even if you do live on a low-carb diet, fasting provides additional benefits:

The very low carb diet does remarkably well, providing you 71 percent of the benefits of fasting, without actual fasting. But sometimes low-carb just isn’t enough. I’ve had many patients who limited their carbohydrates but still had elevated blood sugars. How do you get more power? Fasting. Insulin is the main driver of obesity and diabetes. A very low carb diet can reduce insulin by more than 50 percent, but you can go another 50 percent by fasting. That’s power.

The next several chapters go into more detail about using fasting for specific benefits: to treat type 2 diabetes, to slow the aging process, to boost heart health.

Part Two is the how-to section of the book.  I know, I know: how much how-to information do we need to learn how not eat for awhile?  Well, there’s more to it than you might think.  There’s good advice in here on how to avoid common effects like headaches (salty broths help), who shouldn’t fast (kids, pregnant or nursing women, underweight and malnourished people), and various fasting protocols.

There’s no single protocol that’s best for everyone.  Some people may find they do best with a four-hour eating window, some may prefer alternate-day fasting, some may prefer the 5:2 plan popularized by Dr. Michael Mosley in the U.K, and some may want go to for extended fasts lasting several days or longer.  The book explains each protocol and describes the advantages.

My protocol, in case you’re curious, is to mix Mosley’s 5:2 with 24-hour fasts.  In other words, twice per week I don’t eat for 24 hours, then eat one meal of around 600 calories for dinner.  I haven’t noticed a shift in weight, but I view the fasting as a health regimen.  After seeing Chareva’s father hobbling around our house because of his stroke, I’m more determined than ever to keep the biological machinery from breaking down.

Part Three is the resources section.  There are suggested schedules for various fasting protocols, recipes for broths and teas that make fasting more pleasant, and lots of real-food recipes for meals on non-fasting days.

Like The Obesity Code and Jimmy’s Clarity series, The Complete Guide to Fasting is an easy-to-read, consumer-friendly book that passes my Aunt Martha test.  The science nerds will also be happy to see that each chapter ends with a list of references to studies.

When the book was released, Amazon ran out of stock within days.  There’s a good reason for that: it’s an excellent resource, and word got around quickly.  You may have to wait for a copy, but I believe you’ll be glad you added The Complete Guide to Fasting to your library.

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88 thoughts on “Review: The Complete Guide To Fasting

  1. Howard Lee Harkness

    Hi, Tom!

    Alternate-day partial fasting seems to work best for me. On my partial fasting days, I have a bulletproof coffee (about 300 calories, 98% from saturated fat) before I go to work. And that’s it. Until breakfast time the next morning, when I start with a 500 calorie BPC, and don’t usually have a real meal until lunch.

    On my feeding days, I find that I can’t really eat as much as I would have expected…

    I get a little hungry on the partial fasting days, but not so much that I can’t just ignore it.

    Before my next trip to the VAMC “doctor”, I plan to try a 3-day 300 calorie partial fast, followed by a 2-day water-only fast, to see if it has as much impact on my lipids and blood pressure as I have heard it might.

    I’m not all that optimistic about the hypertension, though. I strongly suspect that is a permanent after-effect of statin poisoning. Even when I was morbidly obese, I never had high blood pressure until after my 2nd round of statin poisoning.

    Good to hear from you again, and I look forward to seeing you on the Low-Carb-Cruise 2017. I’m really sorry I had to miss this year’s cruise.

    — Howard Lee Harkness

    Reply
  2. Becca

    We’ve been listening to Jimmy’s talks on periscope, detailing his fast. My husband and I are almost persuaded. To think, watching your movie all those years ago has brought us here!

    Reply
  3. Bob Niland

    re: Employees who wanted the free cholesterol test were told to fast overnight.

    That’s sort of interesting. Had the hospital been more motivated to inflate head count, they might easily have not specified fasting. As you point out, fasting is often a struggle for people on grain-heavy full-time glycemic diets.

    Consensus cardiology decided 4 years ago that fasting wasn’t necessary for the standard lipid panel, as doing the test postprandial only distorts the sacred fictional LDL-C number by 5%. (http://www.medpagetoday.com/Cardiology/Dyslipidemia/35909) Unfortunately, it distorts the actually useful TG number by 20% (and perhaps more, if the draw is done at the peak of the PP TG curve).

    PSA: Anyone getting a lipid or advanced lipoprotein panel may need to independently choose to fast prior to the draw. And if that’s counter to advice, you probably need to be seeking more a competent healthcare provider as well.

    Reply
  4. Tom Welsh

    The thing that still puzzles me is how the body can supply all the necessary nutrients for health while fasting. (And we know it can, for periods of over a year – remember the documented case of that Scottish man?) To start with, they said that the body runs on glucose alone. Then it became understood that, when fasting, fat could be used instead of glucose. But, we are told, the brain still needs its steady ration of glucose, without which it dies! Over the years the amount of glucose the brain requires has been whittled down, eked out with ketone bodies, but I have never yet seen a scientific claim that anyone’s brain can survive without some glucose. Yet gluconeogenesis, as I have seen it explained, converts protein into glucose – and when you fast for long enough, you run clean out of protein (except that from muscles, etc., which won’t last more than a few weeks and using which will also kill you).

    So how on earth can a person survive when fasting indefinitely (the limit seems to be the amount of body fat you start with)? I can only conclude that the level of ignorance about nutrition and metabolism is even worse than I had feared. 250 years of research, and we are apparently just beginning.

    Reply
    1. Tom Naughton Post author

      I wondered that myself. The triglycerides stored in your fat cells are made of three fatty acids (tri) and one glycerol molecule. As you release and burn the fatty acids, the liver converts the glycerol into glucose.

      Reply
      1. John Velden

        Acetone a spontaneous byproduct of acetoacetate can be converted back to glucose by the liver. A non glycerol source of fatty acid to glucose.
        http://high-fat-nutrition.blogspot.co.nz/2016/08/acetone-to-oxaloacetate.html

        In total fasting nitrogen excretion falls dramatically.
        http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2279566/?page=11
        A significant portion of the remaining fasting nitrogen loss is for maintaining pH, giving a buffering solution reduces nitrogen loss further.
        http://www.ncbi.nlm.nih.gov/pubmed/6287864

        Reply
          1. Anne Mark

            I believe Dr. Fung talks about ( either in one of his books or on his blog) that the protein required for conversion to glucose should come from excess skin. He said that since the start of his clinic he has never had to send a patient for surgical removal of excess skin even though they lost a lot of weight. The body catabolizes it.

            Reply
  5. Tom Welsh

    Oh yes, and one more thing! (as Jeremy Clarkson would say) – how does the glucose produced by the liver through gluconeogenesis make its way to the brain without being gobbled up by all the other tissues along the way?Or does it have little notes attached to it, like the ones office workers put on their food in the fridge, saying “This glucose belongs to the brain – eat it and die!”?

    Reply
    1. Tom Naughton Post author

      In the presence of both fatty acids and glucose, most of your body’s cells gobble the fatty acids and ignore the glucose. That’s why when we eat a meal that raises bloods sugar, the body releases insulin. The insulin doesn’t just push glucose into cells; it also locks up fatty acids. So it’s saying to the cells that otherwise prefer fatty acids, “No, no, no! Those are for dessert later! First you have to eat up this glucose.”

      Once insulin drops (as it does during fasting), the fatty acids are released and most cells go back to preferentially burning fat, thus sparing glucose for the brain.

      Reply
      1. Tom Welsh

        Many thanks for your prompt and very enlightening replies, Tom. As a history graduate with just an interest in science, I have a lot of ground to make up in biochemistry. You have done a great deal to help me bridge the gap between the professors and their books and my own everyday reality. Besides, your blog is just so much fun to read! 😎

        My wife and I still periodically look at each other and intone solemnly: “Follow the money!”

        Reply
        1. Tom Naughton Post author

          My pleasure. I had to learn all this stuff myself while making Fat Head and writing blog posts. Doesn’t do anyone much good if I can’t pass it along.

          Reply
      2. Tom Welsh

        “Once insulin drops (as it does during fasting), the fatty acids are released and most cells go back to preferentially burning fat, thus sparing glucose for the brain”.

        I kept reading and re-reading your explanation. It makes so much sense – what a marvellously elegant system! It’s mind-boggling that “blind” evolution could have come up with something so elaborate and (until the advent of bakeries) foolproof. But of course, on an infinitely smaller scale, that’s what happens when a chess program plays a beautiful combination. It doesn’t comprehend beauty; it just looked at all the possible outcomes down to N-play and chose the best one according to minimax. But because of the way our brains are wired, we find it beautiful.

        And the way our brains are wired is due to “blind” evolution… 😎

        Reply
        1. Tom Naughton Post author

          It is a marvelous system. As we say in the upcoming book, your body’s apps are fine examples of brilliant programming … but apps are written for a particular environment, and industrial foods changed the environment.

          Reply
          1. Walter

            Industrial foods were and are specifically designed to hack our apps. Flavorists, sugar and diabolically supporting anti salt campaigns so that given the body’s need for salt, the elephant will override the rider and go for salty high refined carb snacks with salt. Besides hiding the sugar in cola drinks, this may be the motivation to add salt to the drinks.

            DR, Robert Lustig in his book states that there is a concerted effort to make people confuse pleasure with happiness. Pleasure is dopamine and Happiness is serotonin. Pleasure is fleeting and dopamine down regulates the nerves vice serotonin which relaxes the neurons and thus does not down regulate the neurons.

            Reply
      3. Anand Srivastava

        Peter (hyperlipid) has shown that presence of palmitic acid in the blood stream causes physiological insulin resistance. So when we have low blood sugar, the liver releases palmitic acid in the blood stream so that the cells will not use up sugar, even if insulin is present. Probably why fat is transferred only as triglycerides or ketones in the blood stream.

        Reply
  6. Linda

    Tom, you were definitely a first stepping stone for me with the Fathead movie! I’ll never be able to thank you enough for how you helped me with my health!

    I’ll definitely get the fasting book. Great review. I’m still a couple of books behind in reading, but I’ll get there. I’m finding more and more that I’m fasting intermittently anyway. A while back, since I mostly am responsible for my meals only, I decided that I would eat when I was hungry and not eat when I wasn’t. Yesterday started with a loaded breakfast of fried eggs and sausage, avocado with homemade mayo and coffee with heavy cream. I was never again hungry till this morning. So, the rest of my day yesterday consisted of drinking water and tea. I guess that counts for 24 hours of fasting.

    It took a long time for me to finally give up that ingrained three meals a day at specific times, with snacks in between. But, I’ve finally done it. My only concessions to that are when I take my poor statin damaged elderly Aunt Mary out to lunch- she is convinced that 11 AM is the only time to go to lunch. Says she gets shaky if she waits much longer- of course that is after her breakfast of her beloved toaster pastries and coffee with International Delight creamer and sugar!!

    I’m too am looking forward to your book! Don’t give up the blog, though! I look for posts and read comments every single day!

    Reply
    1. Tom Naughton Post author

      No worries, I won’t give up the blog until I’m either too feeble to write or have no readers left.

      Reply
    2. Walter Bushell

      ” of course that is after her breakfast of her beloved toaster pastries and coffee with International Delight creamer and sugar!!”

      Lard have mercy!

      Reply
  7. Bob Niland

    re: Employees who wanted the free cholesterol test were told to fast overnight.

    That’s sort of interesting. Had the hospital been more motivated to inflate head count, they might easily have not specified fasting. As you point out, fasting is often a struggle for people on grain-heavy full-time glycemic diets.

    Consensus cardiology decided 4 years ago that fasting wasn’t necessary for the standard lipid panel, as doing the test postprandial only distorts the sacred fictional LDL-C number by 5%. (http://www.medpagetoday.com/Cardiology/Dyslipidemia/35909) Unfortunately, it distorts the actually useful TG number by 20% (and perhaps more, if the draw is done at the peak of the PP TG curve).

    PSA: Anyone getting a lipid or advanced lipoprotein panel may need to independently choose to fast prior to the draw. And if that’s counter to advice, you probably need to be seeking more a competent healthcare provider as well.

    Reply
    1. Bob Niland

      re: I practice fasting every day..but I call it sleeping..

      I suspect the book goes into some depth on that. People following low net carb diets are probably getting fasting benefits during every night that’s 16 hours without food.

      My impression is that the fasting period represented by sleeping is of little metabolic benefit to people (probably not you) who are either on a full time moderate- to high-glycemic diet (e.g. SAD) and/or who eat/snack less than 4 hours before sleeping (less than 16 hours total fasting time).

      Reply
      1. j

        Yes the SAD diet is the main problem..no amounts of sleeping or fasting will help that.

        Stress is another problem..which is hard to avoid in present day lifestyles. It triggers subconcious eating and snacking..especially during boredom.

        Reply
        1. Galina L.

          Actually, IF and sleeping most probably will make SAD less harmful. My naturally thin lady friend who ate anything she wanted (like most naturally thin people) started to use eating within 5 hours window after turning 45 as a middle-body fat accumulation prevention tool. It worked.

          Reply
          1. j

            Thats good she got results…not sure about the less harmful part but.. I rather just eat 95% natural and not have to worry about windows and schedules..less stressful and just as effective.

            Reply
            1. Galina L.

              Unfortunately, there are people who feel deprived without eating sugary junk. As far as I noticed, naturally thin people often consume more unhealthy foods than naturally chubby ones. They less motivated to watch what they eat.

  8. Firebird7478

    Vince Gironda was a proponent of fasting and suggested his clients do one quarterly over the course of five days. He also incorporated colon cleansing with it and recommended amino acid tablets to protect from the loss of muscle mass. The drawback, and his disciples still practice this…is to consume fruit juices for energy.

    Reply
  9. Barbara King

    I take warfarin because of blood clots. I was told that if you are on warfarin fasting is dangerous. Does this book address medicines, or is it a more general information book?

    Reply
    1. Tom Naughton Post author

      It mentions that people with type I diabetes and other conditions need to seek medical advice first.

      Reply
    2. Anand Srivastava

      Are you taking omega 3s and avoiding all omega 6s?
      Omega 3s are natural blood thinners and Omega 6s create conditions for blood clots.
      It is the excess of Omega 6 that causes blood clots today.
      Not Vitamin K. Without Vitamin K you would get osteoporosis. And that is one of the major side effects of Warfarin.

      Reply
  10. Robert O Leteh

    Did Dr. Fung mention in his book Dr. Krista Varady’s every other day diet, an alternate day fasting protocol in which dieter eats whatever it wants on feast day and limits calories to 500 on fast days?

    Reply
  11. Galina L.

    Tom, at some point I was convince by you to try IF, and the web-site http://gettingstronger.org/2010/11/learning-to-fast/ motivated me even more. It was a natural next step after adjusting to a low-carbing.Since then I enjoy my freedom from scheduled eating. However, I found out that during prolonged fasts I became too jittery, and any food eaten after a fast which was longer than 20 hours causing a face flash and an elevated heart beat for a short period. Nowadays I just practice shorter 16 – 20 hours fasts. May be my adrenalin goes too high.

    Reply
  12. Robert O Leteh

    Did Dr. Fung mention in his book Dr. Krista Varady’s every other day diet, an alternate day fasting protocol in which dieter eats whatever it wants on feast day and limits calories to 500 on fast days?

    Reply
  13. Galina L.

    Tom, at some point I was convince by you to try IF, and the web-site http://gettingstronger.org/2010/11/learning-to-fast/ motivated me even more. It was a natural next step after adjusting to a low-carbing.Since then I enjoy my freedom from scheduled eating. However, I found out that during prolonged fasts I became too jittery, and any food eaten after a fast which was longer than 20 hours causing a face flash and an elevated heart beat for a short period. Nowadays I just practice shorter 16 – 20 hours fasts. May be my adrenalin goes too high.

    Reply
  14. Mike

    I really enjoyed Dr. Fung’s Obesity Code. My wife and I both started IF, initially with just skipping breakfast a few days a week. We’ve been fans of yours and the Primal/Paleo world since the early days. We’ve been eating real food for some time now, but ever since we started IF we have been consistently dropping weight. We both carry a little more than we should so it was welcomed. It’s been pretty incredibly easy.

    I’m still in the early parts of the book, but one statement that really caught my attention was during Jimmy’s intro. He mentioned a doctor [don’t remember the name now] whose researched seemed to indicate that a singular 7-day, water-only fast once per year could be very beneficial in the prevention of cancer. I know from my Dr. Fung article reading that it has to do with autophagy and the recycling of cells. I just thought that it was very interesting and yet, unfortunately, it’s something you don’t hear about in the “fight against cancer”.

    Reply
        1. Walter

          The red pills and the blue pills are equivalent, just different false worlds run by the machines. The red pill world of heroes fighting the machines is also false.

          No EXIT!

          Reply
  15. Shawn Fennelly

    Tom, I’m a strong believer that even folks w/o a deep science background eventually come to the conclusion, with folks like you informing them, that nature knows best. If our Paleo ancestors didn’t’ survive/thrive with periods of fasting or plenty than we wouldn’t be here right now. 🙂

    Reply
  16. Brand

    The hunger part of fasting was true for me when I started to fast and took about 2-7 days to go away. After that, I’ve never had a problem.

    Reply
    1. Tom Naughton

      The book explains that hunger is partly a conditioned response. It’s the usual time to eat, so we feel hungry.

      Reply
  17. Stephen T

    The low-carb diet seems to be a very easy route into fasting. I really think I’d have struggled before I changed my way of eating. The higher fat content of my diet meant I was regularly going 12 – 14 hours between meals without even thinking about it. After recently reading your thoughts on fasting and those of Jason Fung (and Butter Bob), I decided to extent my fasts to 16 – 18 hours three or four times a week. I know this is a short period for more experienced fasters, but it’s a long way from my cereals for breakfast days. I assume my insulin is lower for longer periods and that this is a good thing? I don’t know if this is long enough for autophagy – an interesting subject. A Japanese scientist, Yoshinori Ohsumi, recently won the Nobel prize for medicine for his work in autophagy.

    Reply
    1. Tom Naughton

      In The Perfect Health Diet book, Paul Jaminet suggests that 16 hours is enough for autophagy.

      Reply
  18. Mike

    I really enjoyed Dr. Fung’s Obesity Code. My wife and I both started IF, initially with just skipping breakfast a few days a week. We’ve been fans of yours and the Primal/Paleo world since the early days. We’ve been eating real food for some time now, but ever since we started IF we have been consistently dropping weight. We both carry a little more than we should so it was welcomed. It’s been pretty incredibly easy.

    I’m still in the early parts of the book, but one statement that really caught my attention was during Jimmy’s intro. He mentioned a doctor [don’t remember the name now] whose researched seemed to indicate that a singular 7-day, water-only fast once per year could be very beneficial in the prevention of cancer. I know from my Dr. Fung article reading that it has to do with autophagy and the recycling of cells. I just thought that it was very interesting and yet, unfortunately, it’s something you don’t hear about in the “fight against cancer”.

    Reply
        1. Walter

          The red pills and the blue pills are equivalent, just different false worlds run by the machines. The red pill world of heroes fighting the machines is also false.

          No EXIT!

          Reply
  19. Shawn Fennelly

    Tom, I’m a strong believer that even folks w/o a deep science background eventually come to the conclusion, with folks like you informing them, that nature knows best. If our Paleo ancestors didn’t’ survive/thrive with periods of fasting or plenty than we wouldn’t be here right now. 🙂

    Reply
  20. Brand

    The hunger part of fasting was true for me when I started to fast and took about 2-7 days to go away. After that, I’ve never had a problem.

    Reply
    1. Tom Naughton Post author

      The book explains that hunger is partly a conditioned response. It’s the usual time to eat, so we feel hungry.

      Reply
  21. Stephen T

    The low-carb diet seems to be a very easy route into fasting. I really think I’d have struggled before I changed my way of eating. The higher fat content of my diet meant I was regularly going 12 – 14 hours between meals without even thinking about it. After recently reading your thoughts on fasting and those of Jason Fung (and Butter Bob), I decided to extent my fasts to 16 – 18 hours three or four times a week. I know this is a short period for more experienced fasters, but it’s a long way from my cereals for breakfast days. I assume my insulin is lower for longer periods and that this is a good thing? I don’t know if this is long enough for autophagy – an interesting subject. A Japanese scientist, Yoshinori Ohsumi, recently won the Nobel prize for medicine for his work in autophagy.

    Reply
  22. Joe Travel

    Hi Tom,

    Is there an explanation of why/how the body does not lower metabolism when fasting versus calorie restriction? I’ve observed this but would like to understand it.

    Reply
    1. Tom Naughton Post author

      Sure, it’s covered in the book. During calorie restriction, you’re still eating and still raising insulin, which signals the body to store calories. Since calories are being stored, your body responds to fewer calories coming in by lowering how many calories it burns. During a total fast, insulin drops the point where calories aren’t being stored — that is, calories are released from glycogen and fat stores — so your body doesn’t need to slow your metabolism to conserve fuel. To put it in a paleo perspective, if you haven’t eaten for awhile, it wouldn’t make sense to slow your ability to produce energy. You’d need that energy to hunt or gather food.

      I suspect, however, that during an extended fast, your body would start conserving at some point.

      Reply
      1. Bryan Harris

        > “…extended fast, your body would start conserving at some point.”

        I have done some long-term fasting (most was 21 days). I always notice I need more and more (and MORE…) coffee the longer I go.

        Not fasting: my normal amount is 1-2 cups of coffee.

        At the end of a long fast (>7 days) I’m always getting around 4 or maybe 5 cups.

        During my longest fast, a cup of coffee gave me extra energy for about 10 minutes.

        I was having trouble at work toward the end, so I came back to reality.

        Reply
      2. Bryan Harris

        I have a (probably wrong) theory about the ketone esters and insulin. I have experimented a lot with those things.

        When I take the esters, it is so many ketones that I wonder if my body makes insulin. I might be wrong.

        I’ve noticed all kinds of barriers to a long term fast with the esters. I’m always SUPER hungry.

        With the salts it’s easier to go right into a fast.

        With the esters, it’s almost impossible for me.

        I don’t have a good explanation. But the best I think of is maybe my body has an insulin response.

        The salts release the ketones slowly.

        With the esters, it really feels IMMEDIATE.

        Reply
    1. Galina L.

      Thank you, Jill, for the link . I have bookmarked it. It should be as often refereed to as a Weston Price work and other classic materials about nutrition and physiology.

      Reply
  23. Bryan Harris

    I guess I’m not technically fasting because I squirt some MCT into my coffee and I also drink the ketones, but I’ve been doing that for a while now and it works very well for me.

    The funny thing is I’m not hungry at work and everything goes okay. When I get home I have a lot of food and my blood glucose jumps to about 115 then back down to about 80 around bedtime.

    When I don’t take the MCT & ketones, I get less done, but I wouldn’t call it brain fog. I just seem to get a lot more work done when I take in that stuff. And then even more if I take vitamin B and fish oils. I can’t confirm nor deny whether I’ve convinced myself that this is all because I’m super-duper smart and my brain needs more fuel than other people. Now if I could just remember where I put my copy of that Dunning-Krueger paper… 🙂

    Reply
    1. Tom Naughton Post author

      I believe you still get most of the benefits of fasting even if you consume a little fat in the morning. You’re still keeping insulin down.

      The paper is in your desk drawer behind the auto-insurance policy. I know because I asked my mom, and moms always know where everything is located.

      Reply
  24. Firebird7478

    For the last few years we’ve been told that low calorie dieting was bad for us and wrecks our metabolism. Fasting seems to me to be a low or no calorie WOE (or I should say…not eating). Now we’re finding out that this is not so bad. Confusing, but if Dr. Fung’s research is correct then there would be validity to Dr. Simeon’s HCG Diet, especially when you consider that there are people advocating a 500 calorie/day “fast”.

    I did that diet in 2008. I went from 183 lbs. down to 160. BF & dropped to 10%. Felt like I was starving all the time. I found myself staring at the jar of mayo in the fridge and craving Domino’s Pizza when a commercial came on the TV.

    But it worked. I suspect fasting will do the same thing and cause the same cravings. Mental note: remove mayonnaise jar from fridge prior to fast.

    Reply
    1. Tom Naughton Post author

      I believe the difference is that with fasting, you eat normally most of the time, which means the body doesn’t interpret it as a food shortage.

      Reply
      1. Firebird7478

        Perhaps, but there are some people who are fasting 3+ days, then there are others who are doing a modified 500 calorie “fast”. It seems to me there is some gray area there?

        Reply
        1. Tom Naughton Post author

          Mosley’s 5:2 is five days of eating to satiety and two days limiting intake to about 500 calories. I suspect eating to satiety most days prevents a metabolic slowdown on the 500-calorie days.

          Reply
    2. Galina L.

      There is a significant difference in the level of hunger when you eat very little and don’t eat at all. Whet you don’t eat you are not hungry after first several hours because your body switches on a fasting mood which keeps constant blood sugar. 500 calories is too much for that switch.

      Reply
  25. Mark S.

    I’ve been on the same fast schedule with Monday’s and Thursdays. I have been fasting for about 20 hrs with my meals ending @ 8PM and fasting until 4PM the following day. My body has grown accustomed to this and I would not get hunger pangs and felt that “no pain no gain” or loss that is. So, I started skipping dinner to and would do a 32hr fast and eat at 5AM the following morning. Even then I feel I could go to lunch time and be OK.
    What I find hard sometimes after the fast is to eat full meals to not create a calorie deficit the following day, so I force my self to eat between fasts. Weird…

    Reply
  26. lydia

    Hi,
    I liked the review and am thinking about buying the book, but I have a question.
    Saw a video with Dr. Ron Rosendal about protein and growth hormone. If I remember correctly he thought increased growth hormone was not good.But from the excerpt in your review it sounded like increase growth hormone was good. And insulin is a type of growth hormone?
    So confused – probably misunderstood. Could you help clarify?
    Thanks,
    Lydia

    Reply
    1. Tom Naughton Post author

      Insulin shuttles protein into cells, and thus is considered a growth hormone. It also makes your fat cells grow. Human growth hormone, by contrast, tends to encourage both muscle growth and fat-burning. Levels of human growth hormone tend to decline as get older. Raising it through diet is probably beneficial for us older folks.

      Reply
  27. Gale

    Very good interesting book, Thank you!

    I did a two alternate day fast for three months. Lost 15#s. Felt great but went back to eating everything. Love to cook and bake.
    Want to get back into this routine, it worked and I felt great.

    A question: Can I take Bulletproof Brain Octane and Collagen Protein powder on these fasting days? Do you counter act the benefits of the fasts?

    Thank you!

    Gale Harpe

    Reply
    1. Tom Naughton

      Dr. Fung writes that it’s okay to include a little fat on fasting days — fat has the least impact on insulin — but not carbs or protein. He recommends bone broths and coffee or tea with perhaps a wee bit of cream.

      Reply
  28. Gale

    Very good interesting book, Thank you!

    I did a two alternate day fast for three months. Lost 15#s. Felt great but went back to eating everything. Love to cook and bake.
    Want to get back into this routine, it worked and I felt great.

    A question: Can I take Bulletproof Brain Octane and Collagen Protein powder on these fasting days? Do you counter act the benefits of the fasts?

    Thank you!

    Gale Harpe

    Reply
    1. Tom Naughton Post author

      Dr. Fung writes that it’s okay to include a little fat on fasting days — fat has the least impact on insulin — but not carbs or protein. He recommends bone broths and coffee or tea with perhaps a wee bit of cream.

      Reply

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