Q&A: who can use intermittent fasting?
, medical review by Dr. Bret Scher, MD
in Dr. Jason Fung, Intermittent fasting 
Do you want to lose weight or improve your diabetes using intermittent fasting? Are you unsure if fasting is appropriate for you?
Dr. Jason Fung, the Canadian nephrologist, is a world-leading expert on intermittent fasting and low-carb, especially for treating people with type 2 diabetes.
Who Can Use Intermittent Fasting?
Is fasting an option for children who need to lose weight?
Fasting is not an option for children. My advice is to severely restrict added sugars and snacking. Reducing down to 2 meals per day is also possible, but not longer duration fasting.
My daughter who is 31 and a healthy weight exercises (rowing) four times a week. She wants to know if she can fast or is this not recommended for people who exercise?
Not only is it safe, but training in the fasted state has several theoretical benefits that many elite level athletes are using. So, yes, it is highly recommended.
Can women fast during pregnancy and after birth during breast feeding?
I don’t advise fasting during pregnancy or breast feeding. There is a concern of nutrient deficiency which I think far outweighs any potential benefit.
How should intermittent fasting be used in conjunction with resistance training to maximize muscle growth and fat burning?
Should there be any differences between intermittent fasting on training days and non-training days? And during the fasting periods – or days – is it advisable to take supplements such as BCAA’s to prevent muscle loss?
There are many different schedules. Most people fast for 24 hrs and then do their training – this is called ‘training in the fasted state’. Since growth hormone is high, you theoretically will recover and build muscle faster in this state.
There is minimal muscle loss during fasting, so BCAA is not needed, but often used by bodybuilders. It’s efficacy is unknown, with mostly anecdotal evidence. Many athletes follow a schedule of 24 hr fast, then exercise, then breaking the fast with a high protein meal.
How appropriate is intermittent fasting for teenagers?
Not appropriate. Certainly occasional short fasts, (less than 24 hours) are fine but not longer ones. Even most religions do not make children fast because their bodies require more nutrients to grow.
Is fasting still a good idea if you are trying to conceive? Should Intermittent fasting be used instead, or none at all?
You can certainly try. Fasting should not be used during pregnancy however.
More Questions and Answers
Go to the page with all top questions and answers or chose a topic below:
- Who can use intermittent fasting (IF)?
- Different variants of IF
- Things to consider during fasting
- Blood sugar and other tests during fasting
- Dietary advice between fasting periods
- Type 2 diabetes (and IF)
- Positive effects of IF beyond weight loss and type 2 diabetes
- Potential negative effects of IF and LCHF
- IF and ketosis
- Recommendations on blood tests
You can also visit Dr. Fung’s website intensivedietarymanagement.com.
Your videos and blogs explain the significance of LC and HF very clearly. What is the role of proteins in this program? I may have missed it, but I haven't seen much mention of proteins. Your website provides information on how much carbohydrate is appropriate; similarly, do you have any recommendations on how much of proteins per day are appropriate and what are the best sources for a vegetarian? Thank you.
If you are a member then you can direct a question to Dr Fung here:
http://www.dietdoctor.com/member/ask-dr-jason-fung
I hope that's OK?!
/Peter Team DietDoctor
I want to thank you for your informative videos. I am 70 years young, but your videos are presented in a way that even I can comprehend most of the information. About 6 months ago my Dr. put me on metformin as I had been pre diabetic for some time, and when my fasting sugars were between 140 and 150 I started taking the medication. I gained weight! hungry all the time. about 2 weeks ago a friend told me about the Diet Doctor website. I was truly impressed. I eased my way into the program and started LCHF in earnest 1 week ago. and I am no longer taking metformin. I check my sugar at home and my fasting still a bit high 135, but after I eat (2hr) from 99 to 114. I have lost 10 lbs I now weigh 257 lbs , I have lost 2 in from waist. I am not hungry at all, keep carbs below 20, and short term fast from 6pm to 12 noon for two days now , think I will continue this. Does that sound reasonable (the fasting times)? I am barely mobile due to congestive heart failure, and other things. I am going to try to get into pool this summer and swim. thank you again for your wonderful life changing information.
Many thanks for your dedication to science and the truth, and presenting it in such an accessible way. I was drawn to fasting originally without a clear motivator. Several years ago I did a couple of longer fasts (7/14 days) just wanting to "cleanse" my body. In the past few years, seeking to address a weight problem, and sometimes being good about LCHF, I started to mix in intermittent fasting of 24 - 36 hours on Day 7 to counteract the one Day 6 "cheat day" that followed 5 days of LCHF. Then I saw your online videos, and bought and read both your books. Wow. Again, thank you.
So toward my question: after absorbing your research and advice, I started more frequent water and tea only intermittent fasting with a fairly flexible approach, just fitting in 16 hour or 24 or 36 hour fasts when I could, but with fairly high frequency. Results started to happen and I was pleased. Then my health club offered a 21 day body composition challenge with a couple cool prizes. With the foundation of a few weeks already of frequent intermittent fasting, that gave me the motivation to go for the 21 day (also water and tea only) fast and really shed the weight and address decades of nutritional abuse (I'm 53, 5'9" and peaked at 198 pounds, just shy of a 30 BMI).
So I am on Day 8 and dropping weight quite successfully - 15.7 lbs as of this morning. What I am struggling with though (besides fairly persistent hunger!) is heartburn. In the reading I've done that seems to be something that should fade away fairly quickly, but it has been nagging me for several days now. In fact, it is more persistent than all but my worst periods of nutritional excess. I am drinking tons of water and include a few teaspoons of apple cider vinegar once or twice a day but the heartburn persists. Any suggestions? Everything else is fine: energy levels high, no nausea, dizziness or weakness, etc.
I'll appreciate any suggestion you might offer.
Cheers,
Greg
Dr Fung,
Can you please update your video links. I can only view the metabolism video and the 'What is fasting video' All other links lead to the "What is fasting video."
My husband and I have been going 3 weeks now with the 20:4 plan, and I have gone from 221lbs to 213lbs! I am a firm supporter of your work, and I'm looking forward to reading the book you wrote when it arrives this Thursday to get more in depth about the research you have done. Thanks for a free alternative to dieting! I've found it's far easier to count minutes than calories!
JennaJ
The links are fine. If you are not logged in to the membership, you can only view the What Is Fasting video.
You can find more info here:
https://www.dietdoctor.com/diabetes
I am on folic acid and Ramipril - will these affect insulin?
if so, am I best to take these during my eating window?
I have been watching the iThrive series, and have been concerned by the comments that the high fat diet ( ketogenic) actually contributes to fatty liver and fat in the cells and over time would make the problem of sugar metabolism worse. Please could you comment and explain how the excess fat is metabolised, does it stay in cells? or is it used by the body and excreted? does the Keto diet exaberate fatty liver or fat in cells?
Are there any tests that could be done before/ after ketogenic diet to allay fears of this problem?
Many Thanks
I read your book, "The Obesity Code," and was fascinated by this new information (new to me). All of the research seemed to make sense. However, I was still left with a few questions. One in particular is regarding people who lean towards hypoglycemia. I desperately want my mom to try more of a LCHF diet along with some intermittent fasting, but she seems to get sick if she goes more than 6 hours without eating something. Could this be caused by a micro-nutrient deficiency? I would love to hear your advice for situations like this.
Respectfully,
Elizabeth
I just wanted to say Thank you so much for the valuable information you have shared on your videos, I credit my success in being on my way to better health on your videos and books. I am a Diabetic, and was getting nowhere, my A1c kept increasing and in April it was at an all time high of 8.9, but decided to bite the bullet and change my diet and lifestyle, watched your videos, read all your books and went on Low carb/High Fat diet with intermittent fasting, I have been able to lose 25 lbs. and I just got my blood work done and have decreased my A1c by 2.5 points and it is now 6.4, my doctor is so pleased she says I am now in the pre-diabetic range and has permanently deleted my Diabetes medications from my patient profile. I know I have a lot more work to do, since my fasting glucoses are still on the higher side, running between 130-150, so thank you so much!
I also want to thank the team on Dietdoctor.com, who has helped me learn about the ketogenic diet, and reading/watching the information you have on your website has also been a major key to my success.
So very grateful to all of you,
Sincerely,
Jeanette
Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis
weird.
Here's the bulk of our information about lchf for Type 1 diabetics - https://www.dietdoctor.com/diabetes/type-1
I am a 63yr old woman using intermittent fasting as an alternative to caloric restriction. I realised, after decades of half starving my body, to keep weight down, after 5 children, that this was the reason for my low energy levels. So thank you for that. I am 5ft 3.5 inches, 114lb, very small frame, BMI 20 and 33% body fat ( after a recent DEXA scan ) and have lean muscle but lack sufficient strength. I use fasting to help acute gastritis and wish to go on a 5 day fast for its health benifits ( autophagy). My questions are; is this okay at my fat percentage and will I risk loosing too much weight ? I have just about overcome my 1970's inherited fear of dietry fat !
Christine from Wales UK
Diabetes. I agree that I put my self in the his position and I also it starts with obesity and understanding it. Thank you so very much for helping me understand what is happening. I’m going to try the intermittent fasting. I went off my insulin for three weeks I lost 15
Pounds went back on it gained 22 pounds in a week and a half. I will go and talk to my doctors and let them know about my test.
Thank you and much mahalo from Hawaii Daniel H Kapika
I know that the advice is to completely eliminate sugar from my diet. However there is coffee and tea I drink with less than one teaspoon (closer to 1/2) I drink a cup. I don't see myself getting rid of that. So it would be nice to know what the effect of small doses has on insulin levels (insulin index). Any idea?
Thanks,
Joshua
PS: Bought the obesity code it was very interesting.
Thank you for your intermitten fasting book. It really helped me. I am hoping you can help me with my kidney? Doctors found aneurysms off of my celiac artery and iliac artery. They are small and not growing so far. I am having a problem with Extremely high blood pressure and found out my kidney is dying on me. The docs told me I can live with one kidney because they don't want to operate. They want to lower my BP with Meds instead. I am taking 40mg of Lisinipril and now two 1 mg tablets of Doxozine at night. Is this effecting my kidneys more? Do you have any suggestions? I want to save my kidney if possible.
Desperate
There is no specific recommended amount of water to drink as it can vary based on many factors.
I was recently diagnosed with insulin resistance at 22, which was a surprise to me. I am overweight, but not terrible unhealthy, and I don't have a family history, or PCOS. Doing intermittent fasting lately, I have lost 15 pounds and am starting to feel good! But I have been monitoring my blood sugar, and am a little discouraged. Yesterday, it was 82 20 hours into an 24 fast, then last night about 1.5 hours after eating, it was 121. But, I took it again 8 hours after eating, and it was 101, and then again 12-13 hours after, and it was 124-129. This fasting blood glucose is actually in the diabetes range, so I was understandably startled. But since my fasting blood glucose is actually as high as my postprandial, does that mean my glycogen stores have been activated and that is what is upping my blood glucose? Could glycogen get them that high? It seems to me that my insulin is working since my postprandial blood glucose is fine, as well as my long term fasting glucose. Do I need to be worried?
Thank you so much for your advice! Your book is genuinely changing my life. You believe in people and help them remove blame from their shoulders, and that is so important. Thank you.
There are many factors that can impact quality of sleep including diet, stress, etc. Consider if your level of hunger and nutritional needs are being supported by intermittent fasting. If so, it is unlikely the sleep issue is related to your diet.
You can start with our free two week challenge!
https://www.dietdoctor.com/low-carb/get-started
If you don't want eggs for breakfast, you can use our egg free breakfast collection.
https://www.dietdoctor.com/low-carb/recipes/egg-free-breakfast
Please consult with your doctor. Dr Fung recommends doctor supervision for extended fasts.
I started to do intermittent fasting 2 year ago and I still continue doing it. I lose 20 kilos. I love my new diet style because match perfect with my circadian rhythm, life style, career and I feel full of energy. I went to the doctor to do an annual check up because every time that I want to break an old habit my body manifest some symptoms like fatigue, anemia, and low energy. I did a test blood and my cortisol was low. My GP is very curious and she wanted to investigate more and she checked other hormones that the adrenals produce and I have the aldosterone in low range. She decided to refer me to an endocrine specialist to know if there are any problem with the kidneys and adrenals. She ordered to do a CT scan to both kidneys and adrenals, they look good. The specialist also order another blood test two times with 3 months separation and the result was the same even increasing my water intake. Also he wanted that I checked my high pressure for 1 month morning, afternoon and evening and the average was 110/122. I am 49 years old. My intuition tells me that can be electrolyte absorption problem because I am not aware which is the amount of electrolytes I need in my diet and how much I required. My window eating is between 12:00 pm and 6:00 pm every day. My doctor don't want to go further because I am a good health and he told me that maybe the reason is hereditary. I start with hemorroides again because I treated them 2010 by surgery and it was my worst decision in life, so painfuuuuuuuul and traumatic. I know that all are connected but I don't know how to understand what really my body wants to tell me. My question is: How do I know wether I am doing correctly my intermittent fasting and how you can help me to correct this if I am doing a mistake?
Thanks
We are not able to provide medical advice. It is best to work with your doctors to address your questions about how intermittent fasting may or may not be connected to your current health concerns.
For reduction in belly fat and metabolic syndrome, check out a keto diet. https://www.dietdoctor.com/low-carb/keto You can incorporate this with fasting as well. See our One Meal a Day guide for tips on how to do this. https://www.dietdoctor.com/intermittent-fasting/omad
I have been a Type 2 Diabetic for over 10 years, earlier this year my blood sugar levels started to gradually increase, I have an insulin injection "Toujeo Solostar" in the morning each day, I gradually increased my insulin to control my blood sugar levels and when I got to 78 units my Doctor suggested that I may have to do 2 injections per day. Fortunately I found your video on the internet and decided to do a 24hr fast 2 days a week ( Monday and Thursday) eg I would eat dinner on Sunday night and not eat anything until Monday night, only coffee and water in between, I never have any insulin on a fasting day. The other days there is nothing special about my diet I try not to go overboard with carbs and sugary foods, drinks and eat plenty of vegetables and very rarely takeaway foods.
I started fasting in April and my blood sugar levels began dropping, after about 7 weeks my insulin injections levelled out to at 58 units per day and my blood sugar level stabilized to around 7mmol/L.
Last Thursday (17th Sept) I woke up feeling a bit wobbly and tested at a low 3.5 mmol/L, this was my fasting day but I decided I needed jelly beans and a substantial breakfast, I have been monitoring my blood sugar levels at least 3 times a day since then and it is consistently around 7 mmol/L and I have not had any insulin since last Wednesday morning (16th Sept), My Doctor can't explain it and is totally mystified, any idea of what's happened?
I have also lost 14kg and seen big improvements in my blood pressure and cholesterol.
Thanks for your great advice.
Check out our guide to low carb and type 2 diabetes https://www.dietdoctor.com/diabetes Pay special attention to the information about starting a low carb diet while on medication.
I wonder if there are any studies about the uric acid retention and its relationship to gout. It seems to increase uric acid retention and reduce excretion. Does this uric acid affect gout?
Here is a very old study: https://www.jbc.org/content/66/2/521.full.pdf
It seems to show that a high-protein diet will increase the uric acid excretion enough to compensate.
However, are there any more current studies showing this as well?
I am not asking for personal advice. However, I am a former gout sufferer (cured by a keto diet) and I am wondering if fasting could send me into remission. On the other hand, combining fasting with keto may be the perfect solution for people concerned about gout.
Your reply would be appreciated.
Thanks for all your videos and sharing.
My dad is 100 yrs old. He got diabetes for many yrs. He was diagnosed with dementia a few yrs ago. My mom has been giving him bean soup as breakfast, congee for lunch and dinner, and that’s with other nutrients like protein.
Recently he refused to eat for a week and got much better but as soon as my mom was able to make him eat, she gave him the same diet. Shortly after this he had one seizure experience.
He’s on both medicines for dementia and epilepsy which makes him very tired all the time. He’s just admitted to hospital due to heart failure. I’m wondering if intermittent fasting and keto diet will still help him. Is it too late to start for a 100-years-old?
Hi, Brian! This video should be helpful for you! https://www.dietdoctor.com/video-post-what-breaks-a-fast
I have read your books and watched some of your YouTube videos. My question is around the value protein in weight loss. With intermittent fasting is it better to increase calorie deficit or protein intake. Or should I focus on increasing both even in leui of intermittent fasting. What should the order of my priorities be? Calorie deficit, then protein then intermittent fasting, or a different order?
Generally speaking, after reducing carbohydrates, it's still important to get adequate protein and nutrition and then fit fasting around those needs.