Fasting: Don’t Make this Critical Mistake | Jason Fung

insulin resistance, diabetes, blood sugar, weight loss

What is the biggest fasting mistake we see in clinic? After a fast, if you over-eat, you'll negate a lot of the benefits. This is a mistake many people make, but also many studies. Several recent studies on fasting make this critical mistake and fail to help clients lose weight. Don't make the biggest fasting mistake. Check out my blog at

More Information:

The Obesity Code – Reviewing underlying physiology of weight loss and how low carb diets and fasting can help.

The Diabetes Code – Reviewing how type 2 diabetes is a reversible disease and dietary strategies.

The Cancer Code – Scientific exploration of how cancer develops –

Canada –

**Fasting Aids**
Pique Fasting Tea (recommended)

Fasting Community and Coaching:

#jasonfung #drjasonfung #fasting #fastingbenefits #weightlosstips #intermittentfasting #drfung #fung #calories #weightlosstips #weightloss #nutrition #diet #health

YouTube Medical Lectures (for specialist physicians):

1. The Roots of the Obesity Epidemic –
2. Therapeutic Fasting – The Two Compartment Problem: ​​
3. Does Calorie Counting work? ​​
4. Two Big Lies of Type 2 Diabetes –
5. Reversing Type 2 Diabetes Naturally –
6. Insulin Toxicity – ​​
7. Saturated Fat – Friend or Foe?
8. Diet and Disease –
9. Dangers of Fructose –
10. Insulin Resistance –
11. Role of Hormones in Weight Loss –
12. The Obesity Code Lecture 1 –

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  • Joe Cabezas says:

    I have been 16-8 hours fasting, with 2 meals a day, for 15 years and have been able to keep my weight stable without hunger.

    • Kane Toews says:

      I wish I knew more about fasting 20 years ago

    • George Taladriz says:

      Same here. Doing keto and fasting for two years now.
      I do, generally, 72 hrs of fasting a week, eat lots of veggies, healthy fat, not much proteins, and do HIIT 5 times a week. I lost the 1.5 year about 12 kg but nothing after that.
      My weight is stabilized now and even if I want to lose more I can’t (?)
      Happy anyway. Lots of energy

    • Bassetto says:

      @Kane Toews better late than never!

    • Kirk Ellis says:

      @George Taladriz I’ve been ketovore since April 2021 with OMAD and some weeks EOD 40:8, mostly eating beef, bacon, eggs, cheese and butter and the occasional salad or veg stir fry. Nothing more strenuous than walking an hour a day. I’ve shed 40 kg so far with another 40 kg still to go. I expect the last 40 kg to take at least twice as long before I hit a stable weight.

    • Rocky Balboa says:

      @Bassetto It’s never too late!

  • Elijah Yang says:

    I have recently started eating just once a day at noon and skipping altogether on Wednesday. It seems a bit extreme but so is my 5’7 350 lb frame. Wish me good luck. Feeling good so far.

  • Sorana44 says:

    I was 230 lbs on sept- oct 2021, Im 4’11” and 55 y/o post menopausal female. I began intermittent fasting eating within a 4 hour period ( 1 pm- 4 pm )and restraint my caloric intake . This really works!! Now on February 2022, I am 186 lbs!! Don’t have sweets addiction anymore and feeling energized again, I was not under 200 lbs since high school!! Love this!!
    Sept 1 2022. I keep loosing weight, feeling great so far, Im now 172 lbs!! Thanks for so nice comments ☺️
    Update october 2022: I’m niw on 172 lbs, some issues with hair loss, but consulting with MD. Otherwise I feel very good thanks for all the encouragement.

    • rick atreides says:

      I’m very happy for you! It looks like you’re doing great. I do have a question though, how hard is it to consistently maintain that window? I don’t get home from my office until about 530, and then after maybe some exercise and unwinding I am pretty hungry for dinner. In your time slot, you’re already done eating for the day. Also, how do you manage that socially as when you go out with friends?

    • Sorana44 says:

      @rick atreides thanks for ur reply
      Tbh I was doing this kind of customized, I mean, I had a span of 4-6 hours to eat and program it according my work schedule u could do that.I work 7-4 so I get to work, drink only coffee at 8, then I continue working and eat the principal meal or high caloric meal at 12 or 1 pm, then When I get home I go to walk or do simple exercise drink plenty water and eat something light or drink a cup if tea at night. I gave noticed the sugar cravings I had just disappear and without noticed I begin to loose weight. I was so surprised. Adapt this to ur time and lifestyle and u would surely see results. Hope u success!!!
      Socially I don’t have issues cause if I had to eat outside I just replace one of my meals and don’t overeat.

    • rick atreides says:

      @Sorana44 Thank you for responding to me! I’m going to give it a try. I don’t have a great deal to lose but I used to be fairly athletic before and it was much easier. Now, not so much. Thank you for sharing your efforts and results. It’s a great inspiration

    • Victoria Albastra says:

      Amazing! Well done!

    • colacino19 says:

      I guess my question for you which might be impossible for you to know is, did calorie restriction destroy your metabolism.

  • Jason Fung says:

    Learn why snacking is the cardinal sin of weight loss in this video –

    • Ron Johnson says:

      So do medication, vitamins, fish oil, affect this as well? Should I take them all at once?

    • mrbb33 says:

      When I break my fast after 16-18 hours the food tastes great! Problem is that I’m getting heartburn
      Not sure if I’m eating too fast
      Any suggestions???

    • Edgar Gudino says:

      I am 48 years old been a type 2 diebetic for bout 10 years now been overweight for just a little longer than that 5.11 height have weighed as much as 325 lbs the last 6 years been 300 to 290. Ok so my blood work came back like i knew it would Cholesterol High, Tryglicerides over 500 and A1c 12… Now in a nutshell April 1st i weighed 289 now April 25th I’m 269 my fasting glucose went from 300’s on the first to 78 this morning my energy level is off the roof… Here’s what I did, ive been doing the 16/8 sometimes 18/6 and eating nutritious minding my carbs, pretty much exactly what Dr is talking bout in this video and I’m on my way too reverse this disease I’m gonna do this just had to share this is real and it work like a miracle

    • Matt Russell says:

      I’m just coming off an extended water fast and now I am doing OMAD, and it’s been awesome!💯👍

    • Jenna Lud says:

      But what if you’re doing ADF? On feast day do you double your calories or eat normally?

  • Old Crow Adventure Co. says:

    2 years ago I was +550lbs. With fasting and keto I’m now down to 330lbs. This really works.

  • Ozy Sjahputera says:

    My experience verified everything that Dr. Fung stated here. I need to lose 10 lbs to get my BMI down to 25.0 again. Started a low carb diet and 16/8 IF last Sunday. I also exercise 5x a week (brisk walking or jogging 4 miles). By Friday that week I had lost just over 5 lbs. Low carb + IF + exercise is a good recipe for weight loss.

  • Truth or Propaganda says:

    Saved my life. reversed my type 2 diabetes. Was the first doctor I listened to. I Was 315 lbs. Addicted to sugar, eating 4 ice cream sandwiches at a time..etc. Was dying, with type 2 diabetes out of control. Now Keto, intermitintent fast ing everyday (18-6) and 1 day a week 24 hour fasting. Now 250 lbs. (6’4″) No diabetes and feel fantastic. been 10 months. I owe Dr. Fung my life.

    • Poco Pico says:

      Good for you! Glad to hear it! Sounds like you’re doing exactly the right things!

    • Andrei FromAlberta says:

      How did you kick your sugar addiction?

    • Truth or Propaganda says:

      @Andrei FromAlberta I made a decision for no sugar. After 3 days it was a breeze but the most important thing is what I replaced all the bad food with. For a while it was Free range pasture raised eggs and canned asparagus. Later Avacados were added and pecans. Pasta and carbohydrates were replaced with meat and leafy green vegetables. Full keto.Oh and I only drink water…ever. It is really not that hard to quit sugar. Or cutting way back on carbs. You feel so great without all the vegetable oil, and breads…its easy really. Tryi t for 1 week. And the thing about Keto is fat is much more satiating which allows you to do 16/8 intermitent fasting.
      When I ate breads and donughts and sugar I still was always hungry.

      Oh and 1 thing. dont think you can replace sugar with artificial sweetners. This will spike your insulin and the #1 key for me was keeping my insulin levels as low as possible

    • Andrei FromAlberta says:

      @Truth or Propaganda Sounds like I’m half way there – 1 year ago I stopped eating all processed SUGAR – chocolate, honey, ice cream… that was difficult, but I quickly felt huge health improvements! The problem is, I still kept eating a lot of Fruits and Carbs… So now it’s time for level 2 and to cut down on the Carbs – will be a challenge but glad others went through it))

    • Andrei FromAlberta says:

      @Truth or Propaganda you mention no vegetable oil… what do you fry with?

  • No Name says:

    Also lets not forget that intermittent fasting is not just about losing weight and worrying about calorie intake. But the big part of fasting is to reverse insulin resistance in the cells

    • B Marshall says:

      Its also about healing what is bad in your body..kidneys, fatty liver, arthritis etc…. not all of us need to lose weight but have health issues. 😢

    • cinnamon girl says:

      Exactly!! I have been OMAD for over 5 years not to specifically lose weight. I am much more interested in the autophagy and disease prevention benefits and having better skin, better cardiovascular health, improved mood, and clearer thinking. More defined muscles and greater strength are just added benefits!

    • Jessica Martin says:

      It’s plain and simple eat as clean as possible and drink water and coffee no sugar 🤷🏻‍♀️

  • pspillow says:

    This is a great clarification for me. I was under the impression that during OMAD that I should try to eat a full days worth of calories. It’s often felt like too much, so this simplifies the process.

  • Cristie Wentz says:

    Recently started 18/6. It fits family schedule and I can stick to it. I feel fantastic. At least half of each meal is vegetables, sweets are fresh fruit. I can’t believe how sugar cravings have disappeared.

    • Maurice Langley says:

      How long before your sugar cravings went away? I crave sugar during feeding time.

    • Mary Nehra says:

      ​@Maurice Langley get a high cocoa solids dark chocolate 70% or above or very low sugar choc & have a couple of squares of it after your meal it won’t spike insulin & will satisfy sweet cravings, it works for me anyway if I really fancy something sweet

    • Linda Birmingham says:

      Just have to watch the amount of fruit you eat. Hemoglobin A1c does not measure fructose glycating the blood cells. It only measures glucose damage.

    • Linda Birmingham says:

      @Mary Nehra I was doing that until I found out how high dark chocolate is in oxalates, lead, and cadmium. Oxalates were causing my fibromyalgia and bladder pain issues. I don’t know how much a few squares raises insulin, but for me, the dopamine hit makes me crave more than that. Darn!

  • VokalPlus by Indra Aziz says:

    this answered my biggest question regarding caloric defisit vs fasting vs BMR. thank you!

  • 2204pc says:

    Jason Fung should be awarded the Nobel Prize of « much good done to the rest of humanity ». There isn’t much financial gain to get for him from what he explains , but what he brings to humanity is priceless. And will be measured at the end of his life.

    • The MAN says:

      _”And will be measured at the end of his life.”_

      And still you would give him a Nobel Prize…

    • Sarah S says:

      Absolutely, what solid, sane and clear direction he gives. Truly rare in a time where big money wants a bite.

    • Gilda Hernandez says:

      Just love this man with his clear and simple breakdown on what could be medical gibberish for many of us… 👏🏽👏🏽💕🙏🏽

    • Hannah says:

      Unfortunately that prize has become a joke long time ago, and should be abolished instead.
      It’s rarely given to people who really deserve it anymore.

    • Keith Zastrow says:

      @Hannah Yep. As soon as Obama got it, everyone knew that award was a joke.

  • Witness Me Furiosa says:

    Type 2 here. A1C 6. No medication. Just started the 14/10. My blood sugar goes up to 163 and then goes to 134 in the last hour. I was worried but now after hearing this I’m gonna keep going! Thanks Mr Fung. My cousin Chance from the Pine Ridge Reservation told me you helped him cure his diabetes with your knowledge. I’m starting to believe…

  • Marz says:

    I was 80kgs in 2018. I started fasting incorporated with a fasted workout that was really very effective. I’m still doing it until now. Current weight 53kgs.

    • Class V A Maths says:

      What type of fasting did u do? Can u please elaborate

    • Marz says:

      @Class V A Maths  20:4 fasting, I eat once a day. I end my fasting at 6 pm. I eat healthy foods, avoid oily foods, and sugary and have fewer carbs. I do a lot of hiit workout. After I shed all those fats , I started to add weights to my workout to tone.

    • Class V A Maths says:

      @Marz Thanks for your reply. I weighed 79 kg. Now I am 74kg in 2 months. Hoping to get to 60 kg

    • Dalene Handel says:

      So encouriging. Im currently doing this. I lost over 10 kg but have another 8 to go

    • Betty Ayanga Kavulani says:

      @Marz, congratulations 🎉. It might sound easy, but I sure know from experience it isn’t.
      I was 69kgs, now stuck at 64.
      My goal is at most, 58kgs. Wish me 🤞🏻

  • Abhishek says:

    I’m from India. I was 106 kgs & lazy. I’m 6.0 feet tall. After watching your videos on weight reduction & exercise, I’ve reduced weight to exact 81.0 kgs in 5 months. I walk 5 kms daily on weekdays, 10 kms daily on weekends in a park near my house. My eat in 18-6 window. I used to think its rubbish, how will survive without food. Now i feel, how stupid i was. Hehehe. I love your videos & watch them, like them whenever I get time from my work. The credit to my weight loss goes to you. You’re awesome !!

    • Gourav Sahni Anand says:

      What you eat in your eating window can you share. It’s so confusing all are saying low crab and as Indian my normal is roti rice dal sabji salad. Not avacado and others

    • Abhishek says:

      ​@Gourav Sahni Anand After watching dozens of videos & going through lot of descriptions I made my own customized diet. I’ll be honest, it was a personal diet. You can’t eat everything nutritious & still lose weight. So, i focused on proteins for 15 days, then healthy fats for 15 days, then walking for 5kms daily. When i gained confidence, I increased my fasting period. I’ll give you my diet, Breakfast – 1/2 bowl Bottle gourd, Ridge gourd, Apple Gourd, sliced onions & cucumbers mixed salad, 4 spoonfuls of Coriander Vegetable chutney, 1 chapati. That’s my breakfast at 12pm. Dinner – same as breakfast at 6pm. Then Keto diet from 6pm to 12pm the next day. I walk 10kms evening 7pm to 9pm with google fit to calculate my brisk walking. 500 metres lap of neighbourhood park in 5 minutes & 30 seconds. i.e. 11mins per km is my speed. In 3 months, I lost 15 kgs…In 4th & 5th month I filled my diet with 1 bowl of pulses or kidney beans daily in breakfast to compensate the proteins in blood. Lastly, 4 litres of water was compulsory in summers & 3 litres of lukewarm water in winters is a must. I’m trying to reach my personal goal of 75 kgs. That’s 31 kgs down from 106 kgs of my peak weight. Hope it helps you. I’ll suggest you to make a diet according to your own doctor & your determination. I was 100% determined to make a difference in my life. And There are 100’s of online videos. But listen patiently for full 45mins or 60mins of Jason Fung, even if it sounds obvious & related to previous videos. I owe my weightloss journey to him. And keep trying to fill nutrients. Hope it helps you. Do make your own chart. Don’t copy mine or you’ll hurt yourself. Okay.

    • Savita .Sriram says:

      @Gourav Sahni Anand vegetables also have carbohydrates but it’s a better type of carb because it’s mixed with fiber and vitamins.
      Eat low refined carb. Eat only Roti or rice , not both. Eat double portion of vegetable and dhal and half portion of Roti / rice. This will still give you carbs but allow you feel full because of the fiber .

    • Gourav Sahni Anand says:

      Thanks for the reply .. I will try my best. I am pure veg (no egg) so was scared about protein but beans and dal will do some help. Didi you take any supplement like in videos they say magnesium and vitd is must … ?

    • Savita .Sriram says:

      @Gourav Sahni Anand yes supplements are a must. VitD, magnesium, potassium, iron ( especially if you are veg) . Protein is important. You can get from nuts, seeds and fats like ghee. Avoid all fruits unless it’s low glycemic. Fruits are a big source of hidden sugars. All sugars are bad for you including “natural” sugars.

  • Stacie Prude says:

    I started at 280lbs in March. Today, May 4th, I’m 237.8lbs.
    I’m a single mom of a rambunctious 5yr old, who I need to feed even while I’m fasting, so anyone can do this! 🎉

  • Uncle Bob says:

    I had recently completed my first 12 day water fast. I had utilized all the foundational information and some from other sources. Due to some health issues specific to myself I struggled a bit but it ended great. Some info:

    -49 Years old
    -10 year Military retiree (for context later). 172 lbs out if boot and 193 at retirement.
    -232 lbs
    -Consistent BP 132/94

    Health issues
    -Hypertension (taking meds)
    -Gall Bladder removal
    -Knee pain
    -Early sighs of diabetes

    Daily action
    -2 liters of water (1 liter smart water in the morning and afternoon and 1 liter in the evening)
    -12oz of water /w 1 tsp of salt each morning
    -1 probiotic capsule
    -1 multivitamin
    -1 prescribed potassium chloride pill (I was low to to the diuretic effects of my BP meds)
    -BP meds

    Day 1-3: Hunger which started tapering off by day 3 but the mind games with myself to quit were frequent.
    -Day 4-5. This is we’re I stopped previously. My gall bladder removal made it so that I had diarrhea while my digestive system emptied itself. Couple that with my BP meds making it a struggle to retain what little salt I tried to keep in my system I got worried. However this time I pushed past it and by the time I was thoroughly ‘empty’ my bile production eventually stopped as did the diarrhea.
    – Day 6 and beyond: From this point I experienced all the normal effects. Chills when only a month ago I felt fine in the same temperature. Minor issues getting 6-7 hours of sleep (previous norm) a night with now 5 being the new norm cause I just can’t stay asleep. Feeling wiped after any decent exertion. Case in point I could 3 sets if 100 calf raises and now I struggled to do even 60 total. However each day I say the improvements which only we as individuals notices as we see ourselves in the bathroom mirror every morning.

    End results
    -206 lbs (26 lbs total loss)
    -BP readings were a consistent 107-110/75-79. This was the biggest wow for me. I’m used to losing weight with new work out reqs and such but I hypertension runs on both sides of my family and I was told having to manage it was my new norm given my age.
    -2 inches off my my size 40 waist
    -Dark skin at the base of my neck disappeared
    -Smaller skin tags are the base of my neck also vanished although a few still remain
    -Face is more angular (A haven’t seen that in almost 5 years.

    End thoughts
    The biggest struggle was the unknown. We are all used to being told how things will pan out everyday for many things and even experienced them ourselves from time to time. But to be able to ‘experience’ it drives home the realize of it. I am now confident that I can do this and I will be doing it again a month from now. Information is our best tool for getting started and tailoring a plan specific to our personal situation is the next best thing.

    If you’ve read this far I wish you the best in your fasting endeavors. You can do this!

    • God’s Tender Mercies says:

      I thoroughly enjoyed reading your comment. Thank you so much. God bless you 🕊❤️🌱

    • Apar India says:

      Thanks for sharing your journey. Very helpful

    • Kristen M says:

      Amazing! Thank you for sharing! 😊

    • Trish says:

      What is smart water?

    • Marica Maas says:

      To help to empty sooner, and completely; also towards supporting the liver’s detoxification function; consider adding coffee enemas (for example in the beginning, middle and end of the fast)? For more info on this: Tony Grandov has an excellent YT presentation about how he had used CE to alleviate his chronic constipation.

  • Rolls Royce Magdale says:

    Started doing IF mid June and walking 10k steps a day. So far, I lost 22 lbs. Will push this until December and see how it goes
    Wish me luck

  • Irish Marie says:

    I started 16:8 two weeks ago and now 17:7. Not snacking was very hard for me at first. I’m now trying to fill up on water and get used to the hunger pangs. I’m not seeing much of a change in weight yet but I’m really trying to be mindful and patient.

  • Dooshima Stone says:

    I aways come back here when I’m doing my monthly 5-7days fast. Thankfully my husband has joined me this time, so I’m happier whilst doing this.

    Back story, I was about 80kg in January this year (2023) and now in October, I am down to between 57-62kg depending on where I am in my menstruation cycle. I am feeling fabulous and always doing physical activities including weight lifting and running…all of which I’m building into a new sustainable habit.

    This may be hard for many but starting is the biggest challenge, then being consistent is when you’ll see results you can appreciate.

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