What is the Best Fast Length? (Fasting Basics 3) | Jason Fung

insulin resistance, diabetes, blood sugar, weight loss

Dr Jason Fung discusses the best fast lengths for you, including 16;8, Time Restricted Eating, 24 hour fasts, One Meal a Day (OMAD), 5:2 diet, extended fasting and more. Shorter fasts are best done more often, but longer fasts (extended fasting) are more powerful. The best fast is the one that fits into your lifestyle. Fit your fasting into your lifestyle, don't fit your lifestyle into fasting. 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:

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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Time Stamps:

0:00 Intro
0:35 How Fasts differ
1:28 Fasting – 3 meals a day
3:16 Intermittent Fasting – Time Restricted Eating
4:04 Intermittent Fasting – One Meal a Day – OMAD
4:50 5:2 Diet
5:41 Extended Fasting

Cameron Long

  • Brian Johnson says:

    I used to weigh 296 lbs …. today I weigh 174 Lbs … where were you 25 years ago … God Bless you for what you do … You are changing lives … With your help I helped my daughter loose 90 Lbs in 5 months …. People this is REAL !!!

    • Simon says:

      What method did she use? 16/8 or longer fasts?

    • Carol Paupst says:

      Thank you for sharing
      I really needed to know if this truly works bc I’m at my wits end tyvm👍😉

    • Fasted Human says:

      that is amazing bro

    • Brian Johnson says:

      @Simon she is trying different ones but she does one 48 or 2 48 per week … she has 2 young children … but she is changing it up …. she uses green olives to get to the ends … they are fat … green olives … pecans … and macadamia nuts are the key to getting 6 more hours in a fast because they are mostly fats …. I eat 1x per day … I do not like the long fast. I use a 2 hour window … or just one meal a day….. I eat mostly low carb all the time … her as well … hope this helps you .. good luck

    • Simon says:

      @Brian Johnson thx. So fat does not trigger Insulin?

  • Jason Fung says:

    Check out my video on why fasting works so well – https://youtu.be/ETkwZIi3R7w

    • fifikhan79 says:

      I did a 93 hour fast because omad stopped working for me. Because I have low thyroid and very slow metabolism. I was getting so hungry and bad cravings because my body couldn’t access the nutrients it needed. My body felt so heavy and movement was becoming very difficult. I had enough and went straight into it.
      On the second day i felt so much better and i was almost scared of re-feeding at the end. I felt the omad working the next day.
      Could you please give more information on re-feeding after a long fast?

    • Pink Supremacy says:

      Dr Fung, is there any concerns about safety when doing a long fast such as 7 days+? Do I need to monitor any blood work?

    • Casabelle Wong says:

      Hi Dr Jason I got no time to make bone broth soup but my mum do make healthy soup almost everyday can I drink the soup to replace the bone broth. Or like miso soup kind. Hope you can give me a reply. I am not obesity but I want to fast as previously I have binge eating disorder due to some stress. So I hope to fast to clear out whatevrr junk food snacks store in my body.

    • education says:

      Dr jason fung sir, I am 39 years old and I have recently diagnosed with diabetes type 2 just 21 days ago and I am very worried about my health, my Hba1c is 7.0, plz help me in choosing the right diet for diabetes type 2 reversal, plz reply

    • aurora571000 says:

      Is there any danger that fasting will bring on mania for a person with Bipolar disorder? Should ppl w bipolar stick w Omad or 2mad and avoid longer fasts?

  • Glee Hanson says:

    You changed my life, Dr. Fung. Seriously. I’m 63 and was morbidly obese for 40 years. I “happened across” your videos over 2 1/2 years ago when my daughter in law scared me to death saying they were fasting as a part of becoming more healthy. I really connected with your message and saw where I was headed. No doubt I would be type 2 diabetic before long. That scared me me further and I jumped aboard and unlike the decades of yo yo dieting I had experienced, I’ve changed my way of eating and I’m never turning back. I’m down 105 pounds and am only 30 pounds from a very healthy weight. I say all that to say this…thank you! Seriously, I can’t express it sufficiently. Thank you.

    • kalina says:

      great job!
      do you eat l ow carb or usually stick to healthy food without thinking too much about carbs

    • Nico Contreras says:

      It´s never too late.

    • Ciaran Byrne says:

      I recently did 12 days and 22 hours water fasting. I went from 15 stone 9 pounds to 13 stone 13 pounds. I ate soup for a few days then started to eat a carb free keto diet and in ten days I am back to 15 stone. I am going to start OMAD and eat at 10am from now on. I will endeavour to get to 14.5 stone using this method. It’s all a learning experience. I was getting very lethargic from day 11. I don’t know how they do 21 days never mind 40. Maybe I will try again water fasting in 6 months. See if I can go longer.

    • Silvergirl7 says:

      This was very inspiring to read!

    • Rola Halawanji says:

      Super inspiring! Thanks for sharing 🙏

  • v t says:

    I started watching Dr Fung’s videos and learned about intermittent fasting 4 month ago and started fasting 16 hrs a day. I would not eat breakfast and start eating lunch at 12pm and stop eating after 7pm. I’m 41 and had fatty liver disease ever since I was 20 years old. I went for a routine check up and had a blood test the other day and for the first time in 20 years I don’t have fatty liver anymore. I was so happy and excited and will never go back to eating breakfast anymore.

  • Hollycat50 says:

    Fasting takes practice. Fasting longer takes a leap of faith. I recently did a 3-day fast and broke a psychological barrier. Now, 36-48 hour fasts are normal and not a challenge. Try a 3-day. And keep trying until you get through it. 👍🥳

    • AmbuBadger says:

      I hear you! I was doing 16-hour fasts and out of the blue I decided to just hold out a little longer without giving myself a definite finish line. Well, I was able to go almost 48 hours, and I didn’t feel bad at all! In fact, I had no brain fogginess or feeling of needing a nap. I found that it helped to have a shot glass of salt handy to dip a fingertip into whenever I felt hungry, a little bit of salt kept my hunger at bay.

    • Kaylen says:

      This is great advice! Three day fasts are a good time period. I’m doing 72hr days consecutively and losing weight like crazy. You get used to the fasting really quick.

    • Hollycat50 says:

      @Kaylen How often do you do a 3-day fast? Just finished my first 87 hr fast and feel fabulous. It really does get easier.

    • Kaylen says:

      @Hollycat50 I used to to 4-5 day fasts, but I can’t sustain that. So now I do anywhere between 24-72 hr fasts. I really try to aim for 72. It’s harder when you do it dry.

    • Kaylen says:

      @Hollycat50 And congrats on your 87 hr fast!!!! Excellent!

  • Maria says:

    It’s kind of crazy that if you eat three reasonable meals a day and no snacking, it used to be normal and now it’s considered a type of daily fasting. It’s amazing how out of control so many people became over the past 30 years. Dr. Fung is helping so many people learn to reclaim their health!

    • 4homemail says:

      I remember those days. It is so true.

    • Me Me says:

      We used to have 2 meals, we were like thoroughbred race horses in the 70’s & 80’s…. Laziness and excessive money leads to excessive eating.

    • Barbara says:

      @Me Me people with less money and lower educations eat more and unhealthy so thats not true

    • A D says:

      I grew up in the 70s and absolutely the norm for all families was 3 meals a day, no snacks, and rare desserts on special occasions. Rich or poor. Every kid brought lunch to school and it was always a sandwich and an apple. A pint of whole milk was provided by the school. Even the inactive children were not overweight.

  • Shaad Dhillon says:

    I’m new to this and have done 16 hour fast daily this week. Was feeling like I was hard-core until I read the comments. Guys here have done days ! Hats off!

    • tom wandersee says:

      Weeks 🙂

    • CT2507 says:

      @tom wandersee yea, its mindblowing!

    • Vicky Autry says:

      Any fast is an accomplishment. It’s not a test, it needs to fit YOU. You can change it up large if motivated to, but you are getting the core benefit with what you’re doing now! Good luck!

    • DW Carvings says:

      Don’t worry friend, I’m in the same boat as you. 16/8 is my daily goal for now and maybe after a week or so I might try throwing in an OMAD.

    • Shaad Dhillon says:

      @DW Carvings Ah thanks. But uou know after doing omad for a week, dismt lose anything!! Yikes. In the past one week of watching what I eat would be enough and now it simply isn’t! Not sure what I need to do
      Ps I’m 45 and a woman.

  • E E says:

    I’m a 38 year old woman, 5’0 and 220 pounds. I’ve lost 15 pounds prior to IF through – a healthy diet, consistent exercise, etc. I eased into it – dropped sweets, then most sugar (still ate fruit), then most dairy (it’s a problem for me). I was eating too much as well so I reduced quantity of food.
    Then I started IF. Easing in with first 18:6 then 20:4 and now OMAD. I’m excited because IF gives me hope.

  • Clohan Mom says:

    I was doing 16:8 for over a year. One day, I got busy and forgot to eat until 19 hours. I realized that I feel just fine so eversince then I extended my fast to 20:4 five days a week. No pain there for me 🙂 My A1C is great and I weight less than I did in high school.

  • Runner2000 says:

    I did OMAD, 3 to 5 day fasts here and there, cut out grains and pasta, kept a good calorie deficit and walked 3 miles a day for 8 months.
    Lost 130 pounds, averaging 4.6 pounds a week.
    By the end, my body was so tuned to it, I could guess my weight 2 weeks out forecast when it was time to go by a smaller pair of jeans.

    • Dee Dee Unkefer says:


    • Ridgeway Julakit says:

      During your 3-5 day fasting, were you still walking or light exercising?

    • Runner2000 says:

      @Ridgeway Julakit
      3 days, yes.
      Anything longer, no.
      Honestly, I did. 5 Day and a 6 Day Fast just to see how it would work
      I wouldn’t do them again.
      It can be dangerous, but a 3-dayer is fine, although you should consult your doctor about it first then practice “Crawl, Walk, Run.”
      Fast for a day just to get your body used to it.
      Then work your way up to 3.
      And listen to your body.
      If you get light-headed, stop.
      If your heart races, stop.

    • Ridgeway Julakit says:

      @Runner2000 Thanks man! I appreciate it. I plan to do some walking when I get to 48 hours, currently I’m on OMAD for a month. I plan to add some light exercise but definitely going to pay attention to what my body will tell me.

    • Runner2000 says:

      @Ridgeway Julakit
      Best of luck to you.
      I would also suggest you get a good multi-vitamin to make sure you’re not getting depleted in any areas.
      Just take the vitamin during your feeding window before you eat so you don’t break the fast.

  • Jim East says:

    I’m 71 and just started fasting. I started by skipping breakfast for 2 days and today I skipped everything. I thought hunger would be much more of a problem. This seems doable now!

    • Trish Kline says:

      Just don’t forget your electrolytes, that’s very important

    • truincanada says:

      It is sir very doable! Especially day 4 when theres no hunger pangs and that will be consistent from that point forward until you wish to break the fast. Its incredible really. And it REALLY works for weight loss and other great physiological benefits! Cant beat it! Keep going!

  • RK's Lounge says:

    Currently on a 62 hour fast and I feel great. Break that psychological barrier and keep going. You GOT this!

    • Undesignated God says:

      Im currently on a 64 hour fast. Only having water when I feel it necessary especially after an hour long sprint/walking. I have a deadline to meet by Dec. 17. I feel great. It really is the psychological barrier. Especially when other people around you are like “yo im gonna ubereats some wendys, get some spicy chicken sandwich” nd then in the back of your head you’re like “damn… Their chicken sandwiches do be slapping sometime” its having the resilience to say no. If everything goes according to plan, I will meet my deadline. Tomorrow is gonna be the first real test to see how strong my resilience is. Wish me luck.

    • Undesignated God says:

      @RK’s Lounge i have a question for you, what did you do with the stomach pain? Not like your stomach growling for food, but just this constant stomach pain. Its weird cause it wasnt occurring the past days until today.

    • RK's Lounge says:

      @Undesignated God I haven’t experienced that actually. For me the first 2 days, it was intense hunger and then it disappeared. Try maybe drinking Coconut Water twice a day. It could help

    • Undesignated God says:

      @RK’s Lounge ok thank you very much.

  • Margarita Felix says:

    58 hours into my fast. Sick and tired of the cravings and the , if I’m really honest, over 50 pounds extra weight. I want to take back control of my appetite and this is the best way to break the physical and psychological barrier. Lost 5 pounds so far! Good luck to all of us fasters!

    • deb ann says:

      Wow, your doing great!

    • Margarita Felix says:

      @deb ann Thanks! I lasted 3 days. Now I am doing 2 day fasts for each week, then OMAD for the remaining days. I refuse to become a statistic, haha. You know, when you hit your forties and you blow up. I don’t want this unhealthy body anymore

    • Anita Knight says:

      @Margarita Felix you’re doing great!!! Water fasting really helped me break sugar cravings addiction and brings tons of benefits. Longest I did was 15 days. First 3 days are hardest mentally. I’d like to implement more omad long term fasting for long term weight loss.

    • deb ann says:

      Good luck to you! You can do it!💝🥰

    • Margarita Felix says:

      @Anita Knight Omigosh! I’m not sure I can stretch it out that long. But my oh my, the benefits really make prolonged fasting an option. I’m thinking the most I can do is five days, because in the weekends family expects me to eat out with them and I’d like to share my one meal for the day with them. You certainly give me inspiration to push the envelope!

  • Monte Whitefield says:

    Fasting 24 hours now. Down 31 pounds in 6 weeks! Doctor, you are a blessing!

    • Matt McCaughen says:

      Good job

    • Shirley Meador says:

      Wow that’s great ! Good job congratulations 🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉 i hope i lose some weight with this fasting 🌹

    • Iliana---DM says:

      That’s great, but at dome point you’ll need to go further… To 36h, 48h, 72h and even 7 day& further. The problem with OMAD is that you will plateau (STAGNATION) at some point and sometimes even gain some weight back if you don’t expend it. Been there!

    • Brian Hampson says:

      ​@Iliana—DM that’s why it’s important to mix up fasting times. Keeps the body guessing.

  • Ramson Cole says:

    I’m 36 days into my 40 day water fast, and I feel fantastic

  • SweetBu Living Life says:

    I am on day 5 of a water and tea fast 😀. I was going to just do 3 days, but am feeling pretty good so kept going and now aiming for 7 days. I’ve been adding sea salt, trace minerals and electrolyte powder to some of the water in the morning. Then just plain water or tea for the rest of the day. I have lost about 11 lbs, which I am very excited about 😁 So far, my longest fast and counting!

    • SweetBu Living Life says:

      I made it to 8 full days of fasting…I’m proud of myself and am going to let this be a good foundation to a much healthier life 🥰

    • hellacat says:

      I’m on day 5 of a fast. Not sure if I should keep going ..but your post is encouraging!

    • SweetBu Living Life says:

      @hellacat Excellent!!! Always listen carefully to your body. It will tell you how far to take anything 🙂

    • Penelope416 says:

      This is encouraging to hear and I’m happy that it’s worked out well for you. I have been fasting for over 24 hours now and working on my second day of fasting. I had a goal to do 5 days of fasting, but I will see how it goes. After the first day I’ve noticed some benefits and felt really good. so I will continue to try fasting for the next 24 hours.

    • SweetBu Living Life says:

      @Penelope416 Great job so far and best wishes 🙂

  • Marty Carmichael says:

    I do a 24 hour fast every Monday and a 48 or 72 hour fast once a month. I didn’t need to lose weight, but I’m very active and it’s really knocked down inflammation in my body.

    • GyK G says:

      Great habit!

    • shinjinisarana09 says:


    • Jody Jackson says:

      Me too !! I do a 36 -40 hour fast every Monday. From dinner Sunday till sometime Tuesday. It definitely gets easier. I’ll do a longer (3-5 days) fast a couple times a year

    • Rey Rey says:

      I’ve been doing intermittent fasting for about a month and decided to do a 5-day prolonged fast. I have chronic inflammation in my chest area for more than a year, but it’s not a big deal because it only hurts when I press on my chest bones. After the 2nd day of fasting, the area of pain started getting smaller. And after 5 days, the chronic inflammation in my chest was all gone. Now, I can press on my bones hard and feel zero pain.

    • Marty Carmichael says:

      @Rey Rey That’s awesome! Let that body heal itself.

  • Yvonne Robinson says:

    Started 18/6 intermittent fast 12/27/22 and today 1/27/23 I’m down 14lbs. No more back pain, no more inflammation in my body. My blood sugar readings are good. I’m in constant ketosis n I’m happy for that. 161lbs today and on my way down. I feel great in my body and I want to thank these doctors for showing us the tools to tap into our bodies own defense and healing.

    • Deanna Howard says:

      So glad it’s working for you.. Doesn’t work for me sadly 😢 I’m on a one month with gaining only with the same method 😢

    • The Tampa Bay No Nonsense Realtor says:

      How are you doing now? I love the 18/6 IF

    • The Tampa Bay No Nonsense Realtor says:

      @Deanna Howard what are you eating when you break your fast? Try to stay away from carbs and sugar when you first break your fast. For example, I’ll break my fast with eggs and a small amount of protein. About an hour later I’ll have carbs.

  • Farlig69 says:

    Currently on day 17 fast and totally loving it! Longest I did before was 12 days. I’m prolly gonna break this on day 20 as that’s half way to my aim of doing a 40 day fast a bit later in the year. Fasting is hands down the best & easiest way to lose weight quickly whilst letting the body heal itself.

  • Yvette Salazar says:

    I am currently at 18hrs fasting for 72hr total fasting. Wow! I am so excited in making this part of my lifestyle. I’ve been abusing my digestive track for too long and I am getting back to a healthy weight. If Jesus did it for 40 days surely 3 days a breeze. May you be Blessed in health n longevity!

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