The Fasting ‘Advantage’ – Part 14

posted in: Fasting, Health and Nutrition | 75

What is the advantage of using a strategy based on intermittent fasting versus simple dietary changes alone – such as the LowCarb HighFat diets that we prefer? There are several good ones.Effectiveness_vs_Simplicity

Reason #1 – Simplicity


When I started out my clinic, I tried to persuade people to adopt the LCHF diet. I was doing this for people of all ages, of all nationalities. It is difficult enough for a well educated English speaking, computer literate person to adopt a strict LCHF diet. This is hard given all the conflicting advice flying around the internet and the airwaves.

We would tell people to go Low Carb and find food diaries full of whole wheat bread and plates of pasta. Many people honestly did not understand the diet at all. I spent lots of time and grey hair trying to change their diets, but many people simply did not understand. Furthermore, their diets had not significantly changed in 40 years, and they were having a lot of trouble changing it.

Since the Low Fat approach had been indoctrinated into them for the last 20 years, it was hard for people to understand how to eat a diet high in natural fats, rather than the low fat fare they were used to. Using a completely different approach such as fasting was much easier for people to understand.

Fasting itself, is so simple that it can be explained in two sentences. Eat nothing including sugars or sweeteners. Drink water, tea, coffee or bone broth. That’s it. Even with this simple method, we (Megan, not actually me anymore) spend hours explaining ‘how to’ fast.

The most obvious benefit to simplicity, though is demonstrated by the startlingly simple graph above. The simpler, the more effective. Amen.

Reason #2 – Cheapwe-love-cheap-sheep

While I may prefer patients to eat organic, local grass fed beef and avoid the white bread and processed foods, the truth is that these foods are often 10 times the cost. Some people, simply put, cannot afford to eat that well.

This is due to the distorting effect of government subsidies on cost of food. Since grains enjoy substantial government subsidies, it is far cheaper to make something out of flour than whole foods. This means that fresh cherries cost $6.99/ pound and an entire loaf of bread will cost $1.99. Feeding a family on a budget is a lot easier when you buy pasta and white bread.

But that does not mean they should be doomed to a lifetime of type 2 diabetes and disability. Fasting is free. Actually, it is not simply free, but it actually saves people money because you do not need to buy any food.

From The Atlantic “Cheap Eats” March 8, 2013

Reason #3 – Convenience

While I may advise people to always eat a home cooked, prepared-from-scratch meal, there are many people who simply do not have the time or inclination to do so. The number of meals eaten away from home has been increasing over the past few decades. While there are many who try to support the ‘slow food’ movement, it is clear that they are fighting a losing battle.

Don’t get me wrong, I love cooking as much as the next guy. But it just takes a lot of time. Between work, writing, and taking my kids to school stuff and hockey, it just doesn’t leave a lot of time.

So asking people to devote themselves to home cooking, as noble as it may be, is not going to be a winning strategy. Fasting, on the other hand is the opposite. You save time because there is no time spent buying food, preparing, cooking and cleaning up. It is a way to simplify your life. I often skip breakfast in the mornings. Man, the time saved! I often skip lunch, too. Man, the time saved! If time is money….

Reason #4 – Cheat days

While I might advise people to never, ever again eat ice cream, I don’t think that is actually very practical advice. Sure, you might be able to swear off of it for 6 months, or 1 year, but for life? And would you really want to? Think about it. Think about the joy that some people get from savouring an especially delicious dessert at a wedding feast. Do we need to deny ourselves that little bit of pleasure forever? Let us all enjoy our birthday salad feast! Thanksgiving kale festival! All you can eat brussel sprouts! Yes, life just got a little less sparkly. Forever is a long time.

Now, I am not saying that you can eat dessert every single day, but fasting gives you the ability to occasionally enjoy that dessert because if you feast, you can balance the scale by fasting. It is, after all, the cycle of life. The reason these ‘cheat’ days are important is because it builds compliance. Simply put, it makes the diet easier to follow and changes it into a lifestyle instead. We often counsel that the most important aspect of fasting is to fit it into your life.

Reason #5 – PowerClenched-fist-300x300

I often treat type 2 diabetic patients. Most of them have had it for 10 years or more. So, of the obese patients I treat, they are often the worst of the worst in terms of obesity and insulin resistance. Sometimes, even a strict LCHF diet is not strong enough. The fastest and most efficient way to lower insulin is intermittent fasting.

In the end, you must ask yourself this question. If you do not eat anything for 1 week, do you think you will lose weight? Even a child understands that you must lose weight. It is almost inevitable. So its efficacy is unquestioned.

There are only two remaining questions. First – is it unhealthy? On the contrary, there are extraordinary health benefits. Two – can you do it? Well, if you never try it, you will never know. I think almost everybody can do it.

Reason #6 – Flexibility

Fasting can be done at any time and in any place. Furthermore, if you do not feel well for any reason, you simply stop. It is entirely reversible within minutes.

Consider bariatric surgery (stomach stapling). These surgeries are done so that people can fast for prolonged periods of time. And they tend to work, at least in the short term. But these surgeries have tons of complications, almost all of which are irreversible.

Furthermore, why would we assume that somebody cannot fast for 1 week or 1 month without ever having tried it?

Reason #7 – Add to any diet

Here is the biggest advantage of all.聽Fasting can be added to any diet. That is because fasting is not something you do, but something you do not do. It is subtraction rather than addition.

You don’t eat meat? You can still fast.

You don’t eat wheat? You can still fast.

You have a nut allergy? You can still fast.

You don’t have time? You can still fast.

You don’t have money? You can still fast.

You are travelling all the time? You can still fast.

You don’t cook? You can still fast.

You are 80 years old? You can still fast.

You have problems with chewing or swallowing? You can still fast.

What could possibly be simpler?

Start here for Fasting Part 1 – Historical Perspective

Continue to Fasting Part 15 – Muscle Mass

75 Responses

  1. Wonderful post, Dr Fung. So you mean I can eat my traditional high carb diet daily as long as I make it a point to fast daily? That would really simplify my life and not be so hard on my pockets.

    Dr. Jason Fung: In the 1950’s, Americans ate white bread and pasta, but made sure to cut all snacks (you’ll ruin your dinner!), and fasted 12-14 hours nightly. It worked well for them. Now, the food production methods have changed, and they also ate much less sugar, but it is certainly a possibility that you could eat a reasonable high carb diet (although still restricting sugar, and try to stick to whole foods) and still remain lean.

    • Thanks for the reply, Dr Fung. I have to admit that I feel less hungry if I ate a low carb meal before the fast. A high carb meal before the fast does make it harder to fast as the hunger pangs and stomach growls are stronger.

      • Margaret Cihocki

        That’s just it, Sarah. intermittent fasting is just so much easier on a low carb high fat adequate protein diet. Because of the satiating effects of the protein and fat. Carbs raise blood glucose and insulin and when the glucose is used up, you’re going to feel some hunger until the insulin comes down and fat burning takes over. IF may be as effective no matter what diet you are following, but it is much much easier with LCHF. But, as Dr. Fung pointed out, it does allow for the occasional higher carb “cheat” meal.

  2. Simon Thompson

    Love the Art Deco Fist- keep up the good articles Jason!

  3. Spot on! As always:-)
    I do wonder though, between 8-10 hours into a fasting day, I get very cold fingers and toes. Also, my pulse goes down a bit. It does generally go away if I drink something hot. Will it eventually go away for good? I’ve only been doing this for about a month.

    Dr. Jason Fung: See response to Sarah below

    • It hasn’t for me… I have been doing a 22 hr fast 5 days a week since the last 2 months or so. My last meal was at 6pm yesterday evening. Even at this moment, I’m feeling freezing cold. And my hands and feet are like ice. The only time the cold feeling goes away is if I go for a walk in the sun.

      Dr. Jason Fung: You may need to change strategies slightly, as your metabolism may be slowing significantly. This used to happen to me too. I added back some days of eating lots of high fat foods (butter, cream, nuts, avocado) to give my body some calories to burn. The weight loss was not as effective, but I felt better.

      • If its because of the metabolism slowing, how about if I do some exercise when I feel cold, like climb stairs, sit ups, etc? Will that prevent the slowing of the metabolism?

      • Dr Fung said “your metabolism may be slowing significantly”. I thought that was to be expected in the CRAP diet as insulin levels remained high due to a constant influx of food and insulin resistance. I’ve been doing the 24 hr fast continuously for over a week now with an avg daily caloric budget of 650 cal/day +/-. Where my metabolism should be, factoring in weight, gender, height, and Benedict-Harris, is 2000/day. Based upon everything I’ve read, largely Dr Fung’s book and posts, the only way one’s (my) metabolism should drop is if my body can not transition past the feeding phase (pg 239). When I have gone to the gym for my routine 60min 3.5mph ‘walk’, that is way more difficult than before. Something else weird is my fbs reading following supper (only meal of day) is generally 106. However my pre-dinner (23hrs later) fbs is routinely low to mid 80’s. I am guessing the morning fbs of 106 is not good as shouldn’t it be normal within 2hrs of eating? Given the strenuousness of the 24 hr fast. At what point should I expect my liver and pancreas to have removed the intra organ fat? The last two nights dinner was a chef salad, 2 deli slices of roast beef, turkey, and ham, a slice of swiss and red pepper, radishes, tomato and lettuce.

        • I should add, according to my scale, I am not losing weight either. How can this be? If my REE dropped to 650, wouldn’t I be hospitalized or…worse? Would subcutaneous adipose tissue blood flow be at all involved with the cold extremities?

  4. I am very glad that I was able to lower the blood 300 to 165 in nearly two months of low carb & fasting.. with out any medication.. I been taking more than 100 of insulin a a medicine.. i would like to thank you a god bless you.

  5. Cassandra

    Dear Dr. Fung,
    In fact there’s another question to add to the two in your point #5–what happens after the fast? Your rather cavalier advice is to act like it never happened, which is very sensible…but my body missed that memo. It’s hungry–for a week or so it’s been way hungrier than it was before I did the 5 and 7 day fasts. My plan to go ahead and do another week quickly fell by the wayside and it’s all I can do to stick to 2-3 LCHF meals per day.

    Besides that, I’m told by a researcher that energy partitioning changes after a fast. As you are rightly fond of saying, your body is not stupid. After extreme deprivation it takes what you eat and shunts more to storage, less to energy, to put back the reserves it was so rudely deprived of.

    So maybe I’m the only fasting failure here, but I’d like to hear from you about the medium to long term rates of weight loss (in borderline obese menopausal women, if possible) on a fasting program. Barring that, some tips for not eating the house post-fast would be nice.

    Dr. Jason Fung: Most patients report a decreased appetite after fasting. Breaking the fast slowly with salad or nuts is another way to prevent the overeating. Most of our patient identify the need to overeat after a fast as mostly psychological rather than real hunger. If it does not work for you, then perhaps try another strategy – LCHF diets, shorter fasts etc.

    • Another thing to take into consideration is how much weight a person has to lose. I’ve done several fasts of three days or longer. One fast, I started at a bodyweight of 154. I got hungrier every day of that fast. Years later I did a three day fast, starting from a bodyweight of 170. That fast was easy. Breaking the earlier fast, I had a tendency to binge. With the later fast, where I had greater body fat stores to begin with–no binge.

      I’ve also found what Dr. Fung says about more fat to be true. I eat low carb, high fat. The day before a fast, I find it useful to go a day or two where I lower my protein a little bit, but not my fat. Usually by increasing my heavy cream. Sort of like an Atkins fat fast, but not calorie-restricted. Low carbers tend to fixate on carbohydrate/fat metabolism as the difference between the fed and fasted states–but a decrease in protein metabolism over the course of a multi-day fast is arguably as, if not more, important.

      • Cassandra I’m also a fasting failure but have found a strategy that works for me..the good old Atkins Fat Fast. 1000 calories of fat broken down in 200 calories every few hours (macadamia nuts/cream cheese/CO/triple cheese brie/cream) etc. Now i thought I wouldn’t last half a day on this and that I would be starving, but it seems to regulate my appetite, cleans the slate, sets me in the right frame of mind. I end up eating less on other days naturally and the weight is finally starting to budge. Also it keeps my BS flatlined all day. You can find the details in Atkins original book, not the newer versions.

        Dr. Jason Fung: There are no failures. If eating more fat works better for you, then do it, by all means. If it does not work, try something else.

    • This is something i was thinking about recently, some thought in probably not coherent manner.

      LCHF: eat when hungry, until satisfied. But after 3 days – week, etc, of fasting, you maybe do not feel hungry, or have shown you do not need to eat, so why eat? Perhaps I am asking what reason is there to break a fast?

      Also, since you get an increase in metabolic rate, is it difficult to overeat when breaking a fast, say you eat something small to break and plan a normal meal a few hours later. Or even would it be possible to under-eat if you break it in this manner?

      One more thing, this is important, and i hope Dr Fung can have some input, have you studied how fasting affects blood clotting, and people who take anti-coagulation drugs.


      Dr. Jason Fung: The only reason to break a fast is if you are becoming malnourished. This usually will not happen with anything less than several months of fasting. Other programs get around this problem, for example with ‘green’ juicing to provide nutrients. There are two main issues in prolonged fasting. First the danger of calorie deprivation. That only occurs in the seriously underweight (4% of less of body fat). Second is micronutrient deficiency (vitamins, minerals and proteins and fats). This is easily remedied with a multivitamin and intermittent rather than prolonged fasting.

      Regarding clotting – I have not seen any good data either way. Again, with the exception of vitamin K deficiency leading to clotting, but that is again remedied with a multivitamin or intermittent fasting.

  6. I agree that fasting was the missing link for me. Your information is the best I’ve found on the topic and gave me the courage to start; I routinely fast 3 days and 4 nights.

    You had also mentioned the Insulin Index in one of your blogs:

    One of the lowest foods on the insulin index, around 13 out of 100, is peanuts. Cheap and easy to roast, if you like. You can even soak them in vinegar for more effect. If you stay with foods with a low insulin index, it is much easier to start and maintain a fast. If I’m eating something with a higher insulin index, I’ll cut the portion and add peanuts to compensate.

    There is a large database on this site:

  7. My wife and I have been performing intermittent fasting for a while now. I started first and then she joined me. We just completed a three day fast together. She made it longer than I did into the fourth day before eating. I find that once my mind tells me it’s time to eat, it’s very difficult to not eat. I did not physically feel as if I had to eat, but mentally I was looking forward to lunch.

    I’ve been eating a low carb, high fat diet mainly, and I’ve been trying to increase my fat content too, as this leads to more satiation without much of an insulin response. I avoid all vegetable oils (other than olive oil on salads) and try to eat fat from animals and coconuts, but mainly animals.

    I agree that it’s difficult to eat nothing but meat and vegetables at times. Sometimes on vacation, for instance, it can be hard to find restaurants without sandwiches or bread-based menus. If you have to meet at an Italian restaurant, as another example, it can be difficult at times to find something reasonable to eat, especially if you’re not fond of veal, chicken, or some fish. As Dr. Fung mentions, parties are particularly difficult, especially ones not thrown by you. In my family, we have three birthdays in three weeks, and who doesn’t want to eat cake or ice cream there? So, intermittent fasting is a benefit there, although I still try to minimize carbs to the extent I can (sugar in any form can be a trigger for me and simply makes me want to overeat). The nice thing to know is that you can get back on the intermittent fasting wagon and still enjoy some parties and traveling and the like.

  8. Dr. Fung

    Did I understand you correctly as saying that LCHF is your preferred method of treating insulin resistance, diabetes and obesity based on your opening sentence, ” such as the LowCarb HighFat diets that we prefer”,
    that fasting is a secondary option based on the difficulties some people have following or understanding LCHF except in the extreme cases you mention in #5 where both may be the best solution?

    Thank you

    • I believe he means that fasting is the best possible intervention, but since we have to eat, he believes LCHF diets are the best possible diet for most people, or at least type-2 diabetics.

  9. Thanks Dr Fung. Just wanted you to know that I am into my third week of intermittent fasting (24hr) that is every second day and some times I do a 36hr fast if I can. I have been able to reduce my insulin dosage (NovoMix 30) from 50 units to 25 units per day. Coupled with a reduced dose of insulin I have adopted a low carb diet – no bread, rice, flour products… This is really working for me and my family are impressed. I am determined to turn my diabetes around. Just one question: I notice that my gums start to bleed on most days that I fast, is there a possible reason for this. Never had this problem before.

  10. 24 months (since May 2013) on very LCHF (<20 g. per day). Lost only 20 pounds the first 3 months and stalled. Two months ago (June 2015) began Intermittent fasting along with the LCHF. Lost 7 pounds in June, another 7 pounds in July, and now at halfway through August 2015 a total of 20 pounds with IF. I was very fat adapted so I've had no problems with sensations of coldness; I have plenty of body fat to feed on. I feel warm and cozy while fasting. Next Sunday, I will be starting my 3rd 5-day fast (every other week). I did have a problem coming off the fasts, felt like bricks in my stomach when I started eating that went away by the 3rd day of eating. Now, going gently, I seem to have adjusted and go off the fasts, even the 5-day fasts, with a minimum of discomfort, if any. Fasts of less than 3 days were like nothing, to easy.

    I measure my ketones every morning with the Ketonix breathalizer. In between fasting I gain a few pounds and my ketone measure slowly go to "yellow" (medium level). While fasting, the ketone measure goes quickly to red, and by the 3rd day fasting is firmly in the "red" (high level). As the fast continues, the Ketonix begins to change from the base level of "blue" (very low to none) to Red level very quickly even before I stop blowing into the Ketonix. I'm thinking that indicates very high ketones, because when not fasting it stays in blue till I finish blowing into the device, then slowly goes from blue, to green, to yellow, and then to red. On a 5-day fast, by the 3rd day the Ketonix is progressing from blue to red before I even finish blowing into it. That's unusual for just LCHF or short fasts.

    • Joanne, what do you eat when you come off a longer fast? I’ve done multiple 3 day fasts, and always have problems after the fast. Basically, there’s nothing in me other than water. My system starts up again, and I have to go to the bathroom 5+ times the first day off the fast (I usually restart at lunch, since I’ve mainly given up on breakfasts). Do you eat a very small meal for the first meal? Do you try to eat lightly the first day?

  11. I haven’t had the courage to try a 3 to 5 day fast or longer, though I would really like to give it a try because I do travel quite a bit and restaurants are very problematic. However for the last month I have done the every-other-day fast, drinking home-made bone broth, and actually beginning my fast at about 7pm one night and going until about 5 or 6pm the next night. That works for me. I still get one meal on the day I’m “fasting.” Just mentally it’s “doable” for someone like me who is totally addicted to eating, because technically I am only skipping 2 meals.

    I have been doing this a month now, and my A1c has dropped from 7.8 to 6.9, and I have dropped about 8 lbs and 2 inches off my hips. And my doctor scaled by my meds a bit. I have gone completely no “GPS” (grains, potatoes, and sugars) with the exception of high grades of stevia occasionally. So the fasting is working for me. I haven’t given up meat and dairy completely, but have cut back significantly.

    I have indulged my sweet tooth with homemade bars and cakes made with almond flours and fruit–all “legal” foods. But have to be careful with that, because I do recognize I get food cravings with I eat too much. Other than that, my food cravings are basically gone!

    I just realize for me I did not want to face a future on insulin with an increasing death threat hanging over my head.

    THANK YOU, Dr. Fung, for making your videos available for free on YouTube! I still watch them. They are changing my life!

    • I find traveling to be a good time to fast. I usually fast traveling to and from my destination, although I still drink water to prevent dehydration. Once I get somewhere, I’m usually with family, so I don’t fast. I haven’t traveled yet for work but plan to do so and likely will include some fasting. Though, I plan to go to Germany, which is great for low carb (lunch meat and cheese for breakfast; sausages and sauerkraut for lunch and/or dinner). If I go to England, I might fast more than I’ll fast while in Germany. 馃槈

  12. Great article Dr. Fung! No more excuses. I have a question: Would it be effective if I did a five days or more fast where I eat 500 or less calories per day?


    • Bernard P.

      As explained by Dr. Fung in the above blog entry, fasting means “Eat nothing including sugars or sweeteners. Drink water, tea, coffee or bone broth. That’s it.”

      If I am eating, even 500 calories or less, I am not fasting. I am restricting calories. Dr. Fung has explained in a previous post that even eating just a little bit can be enough to prevent the body from entering gluconeogenesis (fat-burning mode).

      I was apprehensive before trying a 24 hour fast for the first time, but it turned out to be surprisingly easy. After that, it became a routine. I have one coffee in the morning with 2 teaspoons of of whole milk in it. The rest of the day, I drink water.

      Once I make up my mind that there will be no eating until 6.30 pm, that seems to do the trick. There is no obsessing about being hungry, as I know I just have to wait until the evening meal.

  13. Hi Dr Jason Fung,
    Another great article from you again! However, I have a question. I have been on both Intermittent Fasting and LCHF for 37 days now. I have since loss 18lb. I realise whenever I’m on 16:8 regimen, my weight sort of maintained or reduced just a little. But, when I go on a 24 hour fast, the next day I will drop 1.5lb. Now, I prefer 3 days of 24 hour fast in a week and the rest of the day on 16:8 regimen. During the break fast window, I will restrictly consume only LCHF diet as I’m determine to reverse my type 2 diabetes. Everyday I will choose from fish, pork, chicken, ham, bacon, sausage, cheese, butter (use for cooking), eggs, green vegetables, mushroom, tomatoes, walnuts, moderate berries and moderate peanuts. I have successfully maintain my everyday blood glucose level at 4.4 mmol/L ~ 5.8 mmol/L without anymore insulin or single drugs. My husband has followed me and he has since stopped taking his hypertension pills and his everyday blood pressure is around 116/72, pulse is 65. However, we have yet to check our lipid profile on LDL and HDL. Will these high fats food we consume cause high cholesterol? Thank you.

  14. Thanks for another excellent post. I have found it hard to fast longer than 48 hours at a time, but will keep trying because I agree that the difficulty may be more psychological than real physical hunger. Howeve, even shorter fasts (16 hours every night and 24 hours three or four times each week) have worked well for me and this encourages me to keep trying longer fasts to find out how much more I can improve my health. WE ARE WHAT WE DO NOT EAT!

  15. thank you so much for making your knowledge so accessible via youtube and the internet. I am obese and not losing very much weight doing 16:8 and lchf. Last year I lost weight doing 5>2 and now it is so easy to understand why. Brillant!

  16. Norma Laming

    Give them Dr Eric Westman’s Ketogenic Diet Manual and tell them “only eat the food listed on page 4. If it’s not on page 4 you don’t eat it”.

  17. Quick question. I have been doing the 36 hour fast every other day for just over two weeks now. I notice that my morning fasting glucose is always up at 100 on the morning of my water fast day and stays there pretty much until the next morning when it nudges down to the 90s. Whereas if I eat everyday, it tends to be in the 80s. My post prandials soar into the 200s easily.

    If I ate one triscuit in the morning and then nothing but water the rest of the 36 hours, would the fast still be as effective? I know that one triscuit would trigger just enough insulin to knock the fasting number back for me. But the point is to keep the insulin as low as possible so perhaps I just need to stop worrying about the minimally higher glucose level. It is hard to shift from always worrying about glucose to worrying about insulin!

    Anyone have any thoughts on that single triscuit? Thanks.

    Dr. Jason Fung: I don’t think a single triscuit is a big deal.However, neither do I think a slightly elevated fasting glucose a big deal.

  18. Toni Bissell Legates

    Dr, Fung, I’ve taken your advice to heart and started a 13 day water fast on July 12,2015. I’m a type 2 with poor control on a LCHF diet and after a lot of frustration I ditched the diet and ate what I wanted to for months. When I began I didn’t think I would make it a /ay much less 13. It took 8 days for my sugars to drop from 450-500 to 286 but they edged down from there and by the day I broke my fast. I was getting readings as low as 120. I have now been following a schedule of 20/4 and a LCHF diet. In a month I’ve lost 15 lbs but its edged up and down a lot. What concerns me is my BG readings are super high. for the past week they are constantly between 200-350. I haven’t gotten anything near 120 in the last week. Though my numbers do rise and fall. Which I suppose that means my body is using its insulin. I’m confused and not really sure how to proceed. I’ve been kind of depressed because I thought my insulin resistance would get much better really quickly. I’m doing well with the fasting in fact I’ve surprised myself at what I can adapt too. I’m saving a lot of money on food and the quality of the food I can purchase is much better than the crap diet I was eating. I’ve lost my sugar and bread cravings completely and I no longer need blood pressure medication as I keep a regular check on it. I’m just confused about the rising sugars. A blood sugar of 350 is very high and then it begins to drop after I break my fast each day which is a head scratcher for me. Can you tell me what causes this?

  19. John Caruso

    Dr Fung, Just wondering if you have had any kidney transplant recipients fast to address T2DM / weight loss post transplant? Are there any contraindications for prolonged fasts in transplant recipients? Thanks for your wonderful blog, videos and other fasting related resources. These are truly invaluable.

  20. Hi Dr Fung,

    Firstly, thanks for all the info on your blog posts! I sat enthralled for 2 days reading everything and nearly jumping up and down with excitement as you have confirmed so much I learnt from my ‘alternate’ nutritional studies 20 years ago and taught me so much more! I have 2 questions….the first is how do you know when/if your BSW has reset??? That is my prime reason for starting fasting as I have lost 28lbs and DO NOT want to put it on again!! The second is that although I have never had a problem with increased blood sugar levels its obviously good to keep the insulin levels low too. Is there any way of measuring it to see if the fasting is effective? Thanks.

    • Walter Bushell

      Best way to measure if your insulin level is low is the ketostick. If you are in ketosis, your insulin is low. AFAIK there is no home method for direct testing.

  21. Gunnar Isaksson

    Thanks Dr Fung for another great article about fasting. I have learned alot and all my fears for fasting has wanished.

    I try to fast spontaneously once or twice a week. I do 24-36 hours and once a month 3-4 days of fasting. When I have done a 36 hour fast and feel just great, I then just extend the fast a few more days.

    Normally I will feel warm and in good spirit but sometimes after a few days I might feel frozen and cold. When that happens I wll terminate the fast immeditately since I guess my methabolism is shuttng down. Perhaps I should instead monitor my basal body temperature to be certain?

  22. Thanks Walter. I have been LCHF for 6 months so, unless there is something very wrong, I should be in ketosis but I never use the ketostix and have also heard that unless you are just starting out they are not reliable as a measure after a while. The breath tester is said to be more accurate.
    Do you happen to know why the insulin would be low if you are in ketosis…….especially as things eaten on LCHF can stimulate insulin but not increase your BS?

    • Hi Jane, I am not sure that this is a definite answer but by my thinking, being in a state of ketosis means that you are burning your own stores of fat. If your insulin is elevated then fat storage not burning will occur, hence, no ketones. Just FYI, as I learned the hard way, Drink lots and lots of water…stay hydrated. Hope this helps.

  23. have you ever considered a slow metabolism beneficial from the perspective of aging:?

    I guess 99% of folks dont. If your body runs cooler and at a slower pace, it may run in maintenance mode for much longer that it would if you provide it with plenty of food and focus on “speeding up” your metabolism. folks, challenge the dogma!

  24. I am on my fourth fast (7 day, three day, and four day). So far I am at day three. Usually I am always hot when not fasting but I have been feeling cool if not downright cold during this fast. Extra blanket on the bed and all.

    I finally reached the same actual weight as what it says on my drivers license, with a loss of 35 pounds since May. BG readings have been (depending upon the meter) between 85 and 113, down from 275, while my A1C dropped from 9.5 to 6.5 (Xtra home test). Happy but worried that the coldness is an indicator of lowered metabolism. Any thoughts?

  25. Margaret Cihocki

    Intermittent fasting was half the key to losing nearly 30 stubborn pounds that I couldn’t lose even on a strict Low carb high fat diet. The other half was raising my protein intake a bit and ditching the extra fat (mostly from bullet proof coffees). I’m now at goal weight with normal BMI and more energy and stamina than people a lot younger than I. It was reading your posts, Dr. Fung, that convinced me to go ahead and try IF. I was also able to convince my husband to try it and he has lost 42 lb. and is also at goal weight, with all signs of insulin resistance (he had several) gone. So thank you, thank you! We both intend to continue IF combined with LCHF indefinitely because, as you said, it’s simple, easy, cheap, and all the other things you said above. 馃檪

    • Very inspiring. What was your IF routine and how long did it take to shed the pounds?

  26. Ethan Aquilina

    I’m trying to fast 2 days per week. I have breakfast and then don’t eat again until the next morning’s breakfast (twice per week). Am I doing it right?!

    • You sure are! You’re doing a 24 hour fast twice a week. Whether dinner to dinner or breakfast to breakfast – whatever works for you.

  27. Great article, as usual.
    I would only disagree a bit with the long term health effects of a junk diet combined with IF. That would definitely cause similar deficiencies to what people experience on a SAD, e.g. low magnesium, DHA, K2, etc. I would stick to eating a whole foods, nutrient dense regimen between fasting days, regardless of carb content. That’s not especially inexpensive, but together with the “not eating days” also does not cost significantly more than the SAD. All in all, I suggest that the money saved on fasting days is used for improving quality of food on regular, so called feast days.

  28. I’ve been doing IF for over a month now, starting with 20:4 days, and then moving to a 24-hour fast several days a week. I’m down 22 pounds since I started, and that’s after my weight had been creeping up and up for a couple years on a LCHF diet. On LCHF my blood sugar was pretty out of control also. I’m really hoping IF will help there too though I have not really seen much improvement in a month however – but will keep plugging away.

    I do love the simplicity of IF. I’ve done one 36-hour fast but generally can’t make it past 24. I’m amazed at the folks who can. I love my new food budget too!

    • DebbieC, well done! was your 24-hour fast days in addition to the other days being 20:4?

      • Hi, my 24-hour fasts are generally alternated (so far) with days that vary from 16:8 – 18:6 – or 20:4. It was initially 20:4 every day, but when I started incorporating the 24-hour fasts every other day the alternate days became more like 16:8 or 18:6 rather than 20:4, but I’ll still occasionally have a 20:4 day if, for some reason, I can’t seem to make it the full 24 hours with my fast.

        I’d love to try to fast for longer than 24 hours but have been unable to easily push there yet. I really have to watch my food shopping though! I pay $9.99/month to get free food delivery weekly from a local farm but I’m finding that I’m not sure it’s worth it since I go through food so slowly now. I didn’t even place an order last week as I still had food left over from the week before, and in fact I still have a lot of it left! However since my budget is super-tight right now I guess I love the current amount of food I’m eating, LOL. I just have to decide if the $9.99/month is worth it, though I love buying fresh food locally.

    • Toni Bissell Legates

      Hi DebbieC. I’ve been fasting now since 7/12/15 about 43 days. I began fasting on July, 12th and fasted for 13 days strait. My blood sugars were out of control when I began. When I started my fast ,my diet was beyond poor. I had thrown in the towel on the LCHF diet and not only began eating what ever I wanted to. I also stopped taking my fast acting sliding scale insulin and took only the long acting lantus at nite. So, my readings were very very high at the beginning of the 13 day water/ bone broth fast, averaging between 500-450. It took about 8 days for them to really begin coming down into the 200’s but when they finally got there they kept creeping down until the 13th day I broke my fast with a reading of 120. I then began a 20/4 fasting schedule and stuck to that until today. Today is the first day of a 10 water/bone broth fast. At least that is the plan.

      I noticed you mentioned you hoped your BG readings would come down but they had not really improved much over the month you have been fasting. After initially getting much better numbers on the 13 day fast, I experienced a climb right back up to readings close to 400 most days but never less than 250. With the highest readings being right before I break my fast for the day (20/4). I’m eating very moderate LCHF for one meal and 1 snack during my eating part of the day. I’m dying to talk to someone about their experiences. Could you tell me more of what’s happening with you. As I mentioned, I am again doing a lengthy fast I’m planning to do for 10 days. Though I have to say, I don’t feel well this time around but I’m determined to beat type 2 diabetes! I actually love fasting. Its so much simpler than thinking about food all day long and I’ve completely lost all my cravings for sweets, flour and crap I am not supposed to have. Right now I’m just baffled at the high blood sugars. Anyway, I’d love to hear more of your story.

      Sincerely, Toni Legates

  29. Dr.Fung what would you suggest for folks such as myself that experience a mental fogginess/drowsiness. It sort of a hard feeling to describe, I drink water but still tend to not feel right (mentally) when fasting (20-24 hrs).

    Thanks, Eric

  30. Dr. Fung,

    Have any of your patients experienced hair loss as a result of fasting? If so, why do you think this happens? Since fasting (and low carb diets) lowers insulin and insulin impacts rapidly dividing cells (such as in cancer) — wouldn’t such regimes possibly cause hair loss as hair follicles are rapidly dividing cells?

  31. I have been on LCHF for about two years. After reading Dr Fung’s blog, I have done 4 X 16/8 and 2 X 36 fasts. I am surprised in the lessening of my appetite. Some days I almost dont want dinner. However, I am also sleepier in the 2 weeks I have been on this protocol – could be coincidence. Just turned 60. Weight loss seems to have picked up again after stalling since late spring.


  32. Dr Fung,, I enjoy IF but I read that you must still try to get in your 1200-1500 cal during your eating window ? Is this true,, because there is no way I can do that. I have usually 2 meals a day with IF,, and I practice LCHF as well . I feel satisfied but am I doing any harm to my metabolism . I hate counting cal I don’t do it I don’t want to do it,, I eat until I am full,, and don’t eat again until I am hungry . Can my eating windows vary from day to day . My weekend windows may be different ,, is this ok ?
    Thank you

    Dr. Jason Fung: There is no need to force yourself to eat. I see nothing wrong in what you are doing.

  33. Dr. Fung,

    Just learned of you while watching the LCHF Convention videos. Your lecture was outstanding.

    I have a question about fasting. Setting aside the issue of palatability, do you think a person who fasts for a period of time would cause the identical benefit of avoiding all carbs and proteins (but eating fat) during that period of time?

    I ask because my understanding is that fat causes essentially no change in insulin levels.

    Some might prefer to fast, but others might prefer to have an occasional bite of butter, coconut oil, or that MCT/butter/coffee emulsion that is all the rage among some ketosis groups. Would the latter group receive the identical benefits, in your view?


    Brian G.
    Irvine, California

    Dr. Jason Fung: The so-called ‘Fat Fast’ likely gives most of the benefits of fasting. In our program we also allow a small amount of cream in coffee. However, anecdotally, there are some who report that the added fat reduces their benefits substantially. For most, I suspect the ‘Fat Fast’ works the same, as long as you don’t have protein along with it.

  34. Blood sugar after 36 hour fast was 4.2. (T2D) 2 hours after very low carb breakfast it’s 6.5. Discouraging. Or does that number mean anything?

    • I see this was touched on earlier in this thread, so disregard unless you can add more specific info.

    • @Grant: What does your “very low carb breakfast” look like? There are people who think they eat “very low carb” but they still eat bread and other crap T2’s shouldn’t be eating.

  35. Wondering anyone with T2 how long one can stay without eating. If I don’t eat after five hours my sugar goes down fast..may be up to 3.5 or so which makes me worried.How I can start fasting ?

  36. Dr Fung, Hi I’m new here I have t2D and am overweight, well more like obese 295 lbs, I was 370 at my highest last year I lost over 40 lbs. I also spill protein into my urine so I assume I do have some kidney damage. My sugar is usually between 130. The highest is in the morning or early afternoon before I start eating its as high as 180. (From not eating overnight) my first concern is I was told by the Drs especially the kidney Dr that I should never ever have my body in ketosis, and when I read more about it with type 2 d, you should never be in ketosis and its extremely dangerous. Is that true or I can be in ketosis as when I was younger I lost weight on Atkins but as I got older I can’t even lose weight on Atkins, is that because of t2d? Can I go in ketosis safely, I will do anything to get rid of it. I worry more than anything about kidney failure! Please advise me and any others that have the same problem what works for them. Thanking you in advance Dr Fung

  37. Hi Dr. Fung, please could you say a few words about what effect fasting can have on gallstones?
    The only research I could find seemed to say that fasting longer than about 14 hours started to make the gall in the gallbladder more viscose so more likely to worsen stones. As a tool against T2D would 14 hours fasting be long enough – or would taking possibly linseed oil every 10 hours or so be adequate to keep the fast going and keep the gall more fluid. Thank you.

  38. Joe Dawes

    After reading a spiritual devotional in the morning and getting my dose of the noumenal,
    your posts are next to set my day just right. Your humour as you teach is really inspiring, and there is not a misplaced impartation anywhere. Thanks again.

  39. […] de bonne tenue, et que je vais fouiller un peu. Il y a beaucoup de billets sur le je没ne, dont celui ci qui en indique les avantages et b茅n茅fices et qui coule de source (c’est du je没ne 脿 […]

  40. Dave Bastin

    Any thoughts on taking BCAA’s (Branched Chain Amino Acids in pill form) on a fast day?

  41. Hi Dr. Fung. I am a newly diagnosed diabetic as of 9/26. (FBG 333, A1c 11.3) I was put on Janumet 50/500 2x. At the same time I started intermittent fasting by eating in a 6 hr window (low carb lunch and dinner) 7 days a week. I have lost 10 lbs in 30 days and my FBG is now a consistent 100. Will this fasting protocol eventually reverse my diabetes, or do I need to be on a more aggressive fast.

  42. […] Jason Fung: The Fasting ‘Advantage’ […]

  43. J么natas Silveira de Andrade

    Hello there, Dr. Fung . Well, first things first: I’d like to thank you for all these amazing advice you so kindly provided for free – which I have been recommending to friends and family. I’d like to ask about Low Carb, Adequate Fat, High protein diets – can it be used effectively with intermitent fasting, instead of a LCHF diet? I mean, can a high protein meal break ketosis process and refuel glycogen stores? Also, I’d love to have your posts translated to Brazilian Portuguese (I can do it for free, should you consent), for there is an absolute lack of quality info on dieting and fasting, and all those myths you already pointed out still do prevail on people’s mind here – should I tell someone that I’m 48h on water only, the reaction is always something like “OMG boy, you’d better eat something or you’ll end at the hospital!”. Your presentations exposing the truth of fast have been a huge help for me – once more, many thanks, may God bless you 馃檪

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