Longer fasting regimens – 24 hours or more

untitled-4
This post is about longer fasting periods – 24 hours or more – and how to do them.

I arbitrarily divide it at 24 hours but there is no physiologic reason to do so, other than for classification purposes. There is no magic dividing line.

We covered fasting regimens using periods less than 24 hours previously. The longer regimens are generally done less frequently. The major determinant of which fasting regimen is right for you is personal preference. Some people find longer fasts easier and some find them harder.

Most people find that hunger increases into day 2. At that point, hunger peaks and then gradually recedes. This is important knowledge if you are attempting a longer fast (3-7 days). It is easier to continue knowing that hunger gradually gets better.

Disclaimer: While intermittent fasting has many proven benefits, it’s still controversial. A potential danger regards medications, especially for diabetes, where doses often need to be adapted. Discuss any changes in medication and relevant lifestyle changes with your doctor. Full disclaimer

This guide is written for adults with health issues, including obesity, that could benefit from intermittent fasting.

People who should NOT fast include those who are underweight or have eating disorders like anorexia, women who are pregnant or breastfeeding, and people under the age of 18.

Around one day long fasting periods

24-hour fasts

A 24-hour fast lasts from dinner to dinner, or breakfast to breakfast, whatever you like. For example, you would eat dinner at 7 pm and then fast until the next day’s dinner at 7 pm. In this regimen, you do not actually go a full day without eating since you are still taking one meal on that ‘fasting’ day.

This is very similar to the ‘Warrior’ style of fasting although that allows a 4-hour eating window so is technically a 20-hour fasting period.

This period of fasting has several important advantages. First, as a longer duration fast, it tends to be a little more effective. Because you still eat every day, medications that need to be taken with food can still be taken. For example, metformin, or iron supplements or aspirin should all be taken with food and can be taken with the one meal on the fasting day.

The major advantage of 24-hour fasting is that it is easily incorporated into everyday life. Most people, for example will eat dinner with family every single day. As you still eat dinner every day, it is possible to routinely fast for 24 hours without anybody knowing any different, since it really only means skipping breakfast and lunch on that day.

This is particularly easy during a workday. You simply drink your morning cup of joe, but skip breakfast. You work through lunch and get home in time for dinner, again. This saves both time and money. There is no cleanup or cooking for breakfast. You save an hour at lunchtime where you can work, and be home for dinner without anybody even realizing you had fasted for 24 hrs.

For weight loss, in our Intensive Dietary Management program, we’ll recommend this schedule of 24-hour fasting to be done three times per week. Many people find it so simple they will often increase it to five times per week, and sometimes every day. We also recommend this schedule frequently for those people who are older or taking medications.

One of the main worries of fasting is the loss of lean body mass, or muscle. Many studies have been done on this and these fears are largely misplaced, especially for overweight or obese individuals. In one study, fasting every other day did not produce any loss of lean body mass over 22 days, even as body weight steadily decreases.

The 5:2 diet

untitled-7A related approach is the 5:2 approach championed by Dr. Michael Mosley, a TV producer and physician best known for popularizing this approach. He appeared on a BBC program called Horizon entitled “Eat, Fast, and Live Longer”.

While there had been some fringe interest generated by pioneers such as Martin Berkhan and Brad Pilon, fasting had not really hit the mainstream yet. With the BBC documentary and the book that soon followed, intense interest, especially in the UK followed.

The book, entitled “The Fast Diet” became a best seller in the UK and soon other follow up books were released. The basic diet was not quite a 24-hour fasting period. Instead, the 5:2 diet consisted of 5 days of normal diet. On the other two days, you could eat a total of 500 calories. Those 500 calories could be taken all in a single meal. If, for example, this is taken as dinner, it would be identical to a 24-hour fast. However, you could spread those 500 calories out into multiple meals instead. These two approaches are quite similar and the difference physiologically, is likely quite minimal.

Alternate daily fasting (ADF)

krista_facebook-300x300This is the dietary strategy that has the most research behind it. Much of it was done by Dr. Krista Varady, an assistant professor of nutrition with the University of Illinois – Chicago.

She wrote a book about her strategy in The Every Other Day Diet, although this was not the blockbuster success of the 5:2 diet.

Even though it sounds like you only eat every other day, it is not quite true. You can eat up to 500 calories on fasting days, just like in the 5:2 diet. However, fasting days are done on alternate days rather than 2x per week so it is a more intensive regimen.

heilbronn1The major advantage of this regimen is that more research is available on this regimen than any other. We will consider these studies in more detail in later posts.


Risk of complications of fasts >24 hours

As you progressively go longer in fasting, the benefits accrue faster, but there is also more risk of complications. Since I often deal with type 2 diabetics and hard to treat obesity cases, I tend to gravitate towards longer fasting periods, but you must understand that I always monitor very closely their blood pressures, and blood work and progress. I cannot stress enough, that if you do not feel well at any point, you must stop. You can be hungry, but you should not feel sick.

Another major consideration is that medication must be carefully monitored by a physician. The major problem are diabetic medications because if you take the same dose of medication and do not eat, you will become hypoglycemic and that is very dangerous.

Blood sugars going low is not a complication per se, because that is generally the point of fasting. We want the sugars to go low. However, it does mean that you are overmedicated for that day. You must work very carefully with a physician to adjust medications and monitor sugars. Also, there are certain medications that may cause stomach upset on an empty stomach. NSAIDS, ASA, iron supplements and metformin are the major drugs here.

In general, diabetic medicates and insulin MUST be reduced on the fasting day to avoid hypoglycemia. Exactly how much to reduce it should be overseen by your physician.

I do not recommend anybody who is taking medication to try longer fasts without clearing it with their doctor.
 

36-hour fasts

A 36-hour fast means that you fast one entire day. You finish dinner on day 1 at 7 pm for instance, and you would skip all meals on day 2, and not eat again until breakfast at 7 am on day 3. So that is a total of 36 hours of fasting.

In our clinic, we will often recommend 36-hours fasts 2-3 times per week for type 2 diabetes. From experience, this longer fasting period produces quicker results and still has good compliance. Since type 2 diabetics have more insulin resistance, the longer fasting period is more effective than more frequent shorter fasting periods, although we have had good results with that too.

42-hour fasts and beyond

We often advise our clients to make a routine out of skipping the morning meal and break their fast around noon hour. This makes it easy to follow a 16:8 fasting period on regular days. After a few days, most people start to feel quite normal just starting their day with a glass of water and their usual cup of coffee.

When you combine that with a 36-hour fast, you get a 42-hour fasting period. For example, you would eat dinner at 6 pm on day 1. You skip all meals on day 2 and eat your regular ‘break fast’ meal at 12:00. This is a total of 42 hours.

For longer duration fasts, we often try NOT to calorie restrict during that eating period. Often, as people get used to fasting, we hear very often that their appetite starts to seriously go down. Not up. Down. They should eat to satiation on their eating day.

There’s a very good reason for this decrease in appetite. As you start to break the insulin resistance cycle, insulin levels start to decrease. In response, hunger is suppressed and total energy expenditure is maintained. So – appetite goes down and TEE stays same or goes up. Remember that chronic everyday caloric restriction strategies produce the opposite. Appetite goes up and TEE goes down, likely leading to inferior results.

You can extend fasts much longer. The world record was 382 days (not recommended!), but there are many people who can fast 7-14 days without difficulty. Indeed the Master Cleanse used by Beyonce is simply a variation of the 7-day fast which allows some concoction of maple syrup, cayenne pepper and lemonade.

There are some theoretical benefits of stimulating autophagy, a cellular cleaning process which often requires 48 hours of fasting or more. A state of ketosis may require over 36 hours of fasting to enter. There are many theoretical benefits, including appetite suppression and greater mental clarity. For cancer prevention, some recommend a 7-day fast. Many of these benefits are theoretical and unproven, however. Nevertheless, many have found the 7-day fast much less difficult than one initially imagines.

Earlier

Short fasting regimens – less than 24 hours

More

Intermittent fasting for beginners

Get started video course

In these two short video courses, Dr. Jason Fung guides you into a 24 hour and 7 day fast, respectively. Videos with membership or free trial.[/text_left]

How to Get Started with Fasting – Dr. Jason Fung
The Power of a 7–Day Fast – Dr. Jason Fung

Top videos about fasting

  • How to maximize fat burning
  • The top 5 tips to make fasting easier

Full IF Course

Earlier with Dr. Jason Fung

The common currency in our bodies is not calories – guess what it is?

Why the first law of thermodynamics is utterly irrelevant

How to fix Your broken metabolism by doing the exact opposite

More with Dr. Fung

Dr. Fung has his own blog at intensivedietarymanagement.com. He is also active on Twitter.

His book The Obesity Code is available on Amazon.

The Obesity Code

1 2

81 comments

  1. Julie
    Hello, I am trying to figure out while doing a 24hrs fast OMAD at the 23rd hour I would break it with my 1 meal. In this 1 meal I am confused about the food consumption. If my routine normally is IF 18:6 with 2 meals a day at 1285cals 83g Pro 93g Fat 20g Carb Do you consume this all at once or is it ok to cut in half? Less than 1000cals does not sound healthy to do and with reading about going 35g over in protein that can spike your insulin and kick you out of ketosis. How would you handle this situation? I am 42yrs female, 135lbs at 5'3 height, my goal is to be 125-128lbs. I really want to nail this Keto plan and have myself under control properly but there is so many dif opinions out there that has me always 2nd guessing and changing what to do with myself. I finally got my macros to what works with my body I am always reaching my protein goal, and my carbs are always under 20g, my fat I play around with usually lower than my Protein as I was told 70-93 fat to stick with. Any help would be much appreciated. Thank you!
  2. Kristin Parker Team Diet Doctor
    There is no one right answer for everyone. Our number 1 tip is to eat to hunger. For whatever meal you are eating, eat until your hunger is satisfied; that amount is going to be different for different people.
  3. Cristine Gutierrez
    I’ve been on the16/8 since Mid January and I’ve lost 29lbs. I just finished my first 24 hour fast and it really wasn’t as hard as
    I thought it would be. I’ve hit a plateau and I just have 15 lbs to reach my goal so I’m hoping fasting longer will help me break the stall. This is definitely a lifetime process for me, I’ve struggled for the last 14 years to get this weight off. Finally I’ve found something that works and is good for me.
    Reply: #57
  4. Ruchi
    He’ll read the book Obesity Code!! For how long can I continue with alternate day fast or one meal a day fast daily. What should be the follow up plan ? Please suggest
    Replies: #55, #61
  5. Ruchi

    He’ll read the book Obesity Code!! For how long can I continue with alternate day fast or one meal a day fast daily. What should be the follow up plan ? Please suggest

    I meant ‘I have read the book’

  6. Ruchi
    would request to respond asap.
    How long can be the feeding window if I am doing 36hrs fast. *3 times in day.

    How does fasting affects the periods? Are they delayed initially ?
    Thanks I advance.

    Replies: #58, #62
  7. Andy

    I’ve been on the16/8 since Mid January and I’ve lost 29lbs. I just finished my first 24 hour fast and it really wasn’t as hard as
    I thought it would be. I’ve hit a plateau and I just have 15 lbs to reach my goal so I’m hoping fasting longer will help me break the stall. This is definitely a lifetime process for me, I’ve struggled for the last 14 years to get this weight off. Finally I’ve found something that works and is good for me.

    Cristine, are you eating keto during your eating window? Could you post a bit about how you're eating and any exercise?

  8. Kristie Sullivan, PhD Team Diet Doctor
    If fasting is causing missed periods, then you might want to discontinue fasting, as this sounds as if extended fasting is having a negative impact on your body.
  9. paz moreno
    Hola Martha.
    muy interesante.
    me gustaría saber cómo rompiste con ese ayuno tan largo y como reaccionó tu digestion.
    gracias
  10. Derya
    Hi everyone,
    being a keto doctor myself I recently followed the podcasts featuring Megan Ramos, co-founder of Dr Fung’s Intensive Dietary Management, and I learned a lot from her.
    Like eating an avocado every day leading to your fast, so you have enough potassium knocking around. Breaking your fast with some olives and half an hour or so later have your keto meal. On fast days I’ve started carrying with me a tiny box (think salad sauce containers from those pizza deliveries in your previous life) filled with 1,5 teaspoons of Himalayan salt, as getting tired/dizzy/experiencing low blood pressure is my main problem on fasts; I take a few pinches whenever I feel this way.
    Klick on your podcast app, search for “Fasting Talk”, ignore the hosts mostly ‘funny’ side talk and listen up when Dr Ramos answers those questions. It’s from 2017 and she joined till Episode 20 or so, intermittently joined by Dr Fung too. She’s a great resource, working directly with the hundreds of patients and BEING the very first patient herself.
  11. Derya
    OMA (one meal a day) are excellent and you don’t have to limit them as long as you have reached your weight goal.
    If you continuously eat that way, your body gets used to the lower calories and settles for them. You stop losing weight on that regime.
    Dr Fung suggests shaking it up vigorously. Have a few fast days with water and salt only, then again feast like there’s no tomorrow and have keto food three times a day until you are really full.
    Don’t let your metabolism get used to the same rhythm/calories day in day out.
  12. Derya
    As to changes in periods, I’m adding a link to Dr Ramos.

    http://fslmodern.com/2017/02/17/intermittent-fasting-megan-ramos-47/

  13. John
    Suppose I fast for 12 days. Do I need to be careful with reintroducing food? I haven’t found a video on this but there was a documentary on fasting on amazon that said it can be dangerous?
    Reply: #64
  14. Kristin Parker Team Diet Doctor

    Suppose I fast for 12 days. Do I need to be careful with reintroducing food? I haven’t found a video on this but there was a documentary on fasting on amazon that said it can be dangerous?

    Yes, you would want to reintroduce foods gradually. Also please note that Dr Fung recommends extended fasting, especially if on medication, should be supervised by a doctor.

  15. Jade
    Is it safe to drive while fasting >24 hours? In the guide you've put about working through lunch and coming home, but if I am commuting by car is there any concerns?
    The longest I have done is 36 and I didn't feel unwell, but if I am going to attempt this weekly, I want to be sure I am doing it correctly
    Reply: #66
  16. Kristin Parker Team Diet Doctor

    Is it safe to drive while fasting >24 hours? In the guide you've put about working through lunch and coming home, but if I am commuting by car is there any concerns?
    The longest I have done is 36 and I didn't feel unwell, but if I am going to attempt this weekly, I want to be sure I am doing it correctly

    That is going to vary from person to person. If you are unwell enough to drive, the fast should definitely be broken.

  17. Aaron
    Healthy male, no medication/illness, a little overweight but not significantly. How frequently can I do 72 hr fasts? Is twice a month ok? Weekly too much? Obviously need to listen to my body but curious about any official recommendations.
    Reply: #71
  18. Jennifer
    I am considering the 24 hr fast 3 times a week along with Keto. My question is, will adding heavy cream to my coffee end my fast? I have been able to eliminate sugar, but that cream has kept me sane. Also, is there a recommended amout of time for fasting (3 weeks or longer) or shold this be done for short ammounts of time with breaks? I want to make sure I know what I'm doing before I start. Thank you!
    Reply: #69
  19. Kristin Parker Team Diet Doctor

    I am considering the 24 hr fast 3 times a week along with Keto. My question is, will adding heavy cream to my coffee end my fast? I have been able to eliminate sugar, but that cream has kept me sane. Also, is there a recommended amout of time for fasting (3 weeks or longer) or shold this be done for short ammounts of time with breaks? I want to make sure I know what I'm doing before I start. Thank you!

    Dr Fung says that anything more than 1-2 teaspoons of cream may break a fast. Different methods of fasting can work for different people so it can take some experimentation. If you are on any medication you should consult with your doctor before beginning fasting.

  20. Ian
    I have been doing a 16-8 fast but I usually fast 17-18 hours. In the am I have a 20 oz organic decaf coffee with 2 table spoons of heavy cream and 1 table spoon of MCT. I drink this in a Yeti cup that stays hot. This allows me to drink it slow over 4-5 hours. My question is will the MC kick me out of fasting?
    Reply: #72
  21. Kristie Sullivan, PhD Team Diet Doctor
    Hi Aaron,
    For extended fasts, we recommend working with a medical professional.
  22. Kristin Parker Team Diet Doctor

    I have been doing a 16-8 fast but I usually fast 17-18 hours. In the am I have a 20 oz organic decaf coffee with 2 table spoons of heavy cream and 1 table spoon of MCT. I drink this in a Yeti cup that stays hot. This allows me to drink it slow over 4-5 hours. My question is will the MC kick me out of fasting?

    Dr Fung recommends limiting cream to 1-2 teaspoons.

  23. Cindy A Hampton
    John after that long of fasting introduce beef or chicken broth back into your first "foods"
  24. Alvaro
    Hi, I have been tryoing a 16h-8h restricted time diet for 2 weeks and am happy. I want to try a 5:2 diet now. On the days I do not fast, can I also keep doing 16-8 or should I eat throughout the day? Thanks!
    Reply: #75
  25. Kristin Parker Team Diet Doctor

    Hi, I have been tryoing a 16h-8h restricted time diet for 2 weeks and am happy. I want to try a 5:2 diet now. On the days I do not fast, can I also keep doing 16-8 or should I eat throughout the day? Thanks!

    The description as written says 5 days of normal keto eating and does not reference any time restriction.

  26. Sharon
    Hi - Ive done 3x 24 hr fasts, one each week. The first one I lost 0.9kg, the second, 0.6kg, and the third zero. . On the other days I do mostly 16:8, and keep to 20carb, 85fat, 65 prot. Im a 62 year old female weighing 67.5 kg, and would like to lose another 2kg. Is this a plateau I need to work through? Or could I do something differently? Thank you, Sharon
    Reply: #77
  27. Kristin Parker Team Diet Doctor

    Hi - Ive done 3x 24 hr fasts, one each week. The first one I lost 0.9kg, the second, 0.6kg, and the third zero. . On the other days I do mostly 16:8, and keep to 20carb, 85fat, 65 prot. Im a 62 year old female weighing 67.5 kg, and would like to lose another 2kg. Is this a plateau I need to work through? Or could I do something differently? Thank you, Sharon

    Hi Sharon, you can read some great troubleshooting tips in the two articles below.
    https://www.dietdoctor.com/how-to-lose-weight
    https://www.dietdoctor.com/top-tips-lose-weight-low-carb-women-40

  28. Janet
    Hi here- I've been on 18 and 36 hour fasts. At what point in a fast does autophagy start? Once started, does it last the length of the whole fast?
  29. Barbara Guerpillon
    I'm doing 16:8 everyday for 3 months now. I love it.
    I'm thinking of introducing 2 times a week of 36 hours fast which means 42 hours. What is the benefit of it? Is there any knowing that it's only "twice" a week vs everyday ?
  30. 1 comment removed
  31. Stan Gremillon
    "appetite goes down and TEE stays same" and "Appetite goes up and TEE goes down"...
    What does TEE stand for?
    Thanks!
  32. Gentiann
    Total Energy Expenditure
    Reply: #83
  33. Stan Gremillon
    Thanks Gentiann!
    The answer was in the article and but I didn't make the link...
  34. Alma
    what if your doctor doesn't support this program? i'm having a ct scan on my kidneys and getting more meds added to my list, i don't want. I've tried this before for about 2 wks but didn't see my sugars decrease so i went back on my meds.
1 2

Leave a reply

Reply to comment #0 by

Older posts