Q&A: who can use intermittent fasting?

Ask Dr. Jason Fung

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:

  1. Who can use intermittent fasting (IF)?
  2. Different variants of IF
  3. Things to consider during fasting
  4. Blood sugar and other tests during fasting
  5. Dietary advice between fasting periods
  6. Type 2 diabetes (and IF)
  7. Positive effects of IF beyond weight loss and type 2 diabetes
  8. Potential negative effects of IF and LCHF
  9. IF and ketosis
  10. Recommendations on blood tests

You can also visit Dr. Fung’s website intensivedietarymanagement.com.

1 2

58 comments

  1. Kathy McQuiston
    I just watched an interview on YouTube from a few months ago. The host made a comment about how life expectancy has risen. I was surprised that you did not reply with the facts that those people who are living into their 80s and 90s were born in the 40s and 50s. They were receiving the benefits of vaccines and ate 2-3 meals a day. The moms stayed home and cooked healthy meals. Many of those men worked in offices, not in factories or manual labor. Mom continued to cook the same. Those of who were young adults or born after the 70s and followed the pyramid will probably not live as long. I have your books and fasting has saved my life. Thank you for providing the information that has been withheld for so long.
  2. 1 comment removed
  3. Doris Yu
    Dear Dr. Fung,
    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?
  4. Brian Fritz
    Hi Dr. Fung, does a cup of coffee with a splash of milk or cream interrupt the fasting period? For example does a 10 hour overnight fast, cup of joe, and 4 hours fasting after = 14 hours or technically just 10? Phrased more scientifically, I guess I'm wondering if there is a minimum caloric threshold to be in a fasted state, or is it basically "zero"? Thank you.
    Reply: #55
  5. Kerry Merritt Team Diet Doctor

    Hi Dr. Fung, does a cup of coffee with a splash of milk or cream interrupt the fasting period? For example does a 10 hour overnight fast, cup of joe, and 4 hours fasting after = 14 hours or technically just 10? Phrased more scientifically, I guess I'm wondering if there is a minimum caloric threshold to be in a fasted state, or is it basically "zero"? Thank you.

    Hi, Brian! This video should be helpful for you! https://www.dietdoctor.com/video-post-what-breaks-a-fast

  6. Al
    Hi Dr Fung,
    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?
    Reply: #57
  7. Kristin Parker Team Diet Doctor

    Hi Dr Fung,
    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.

  8. Sonja
    Hi Dr. Fung,
    I would love to know your thought on Nutcracker syndrome. I've donated a kidney and have no more pain but now have other issues. It's very hard to find information and physicians to guide me.
    Can you share is a fast would benefit my one kidney and what foods would be best for me?
    Thanks
    Reply: #59
  9. Kerry Merritt Team Diet Doctor

    Hi Dr. Fung,
    I would love to know your thought on Nutcracker syndrome. I've donated a kidney and have no more pain but now have other issues. It's very hard to find information and physicians to guide me.
    Can you share is a fast would benefit my one kidney and what foods would be best for me?
    Thanks

    Hi, Sonja! To contact Dr. Fung, you may want to try his website. https://www.thefastingmethod.com/

  10. Kellie Druken
    I would consider myself a FASTING expert. I read all your books in 2018 and started fasting on and off. I have done many fasting cycles including a 21 day fast and a 19 day fast along with many 3–5-day fasts. I have even completed 3 times a 60-day OMAD in 2019, 2020 and 2021. At the end of 2021, I lost 67 pounds, I have a total of 100+ pounds to lose but in January 2022-April 2022 I was NOT as strict with my sugar intake or my fasting regiment therefore in April 2022 I woke up in pain and was severely sick. After going to the emergency hospital 3 times, tests revealed I had an infection in my ovaries, stones in my gallbladder, Fibroids, and the worst one, very high protein in my kidneys. I spent 8 days in hospital on IV Antibiotics and then sent home on antibiotics for 2 weeks. To this day my ovaries are still infected, which my OBGYN wants to remove, I still have the stones and fibroids although I do NOT have pain from them but the protein in my kidneys is extremely dangerously high (Albumin/Creatinine highest was 141.1 and most recently it is 75.9 mg/mmol), which doctor wants to do a biopsy on my kidneys. So, I am now on a list to have my ovaries removed, Gallstones removed and a Kidney biopsy, which I do NOT want to do and believe if I had the correct doctor all my issues would go away with fasting.
    I have been told by a Naturopath and a doctor that they think all of my issues stem from all the fasting I have done over the years. I do NOT believe that because I felt the healthiest when fasting after losing weight.
    Since you are a Nephrologist and understand the significance of fasting for health, I was hoping you could provide some guidance. I asked my doctor to send a referral to The Metabolic Clinic for me and she has but there is an 8-9 month waiting list. I am most concerned with my kidneys and I need your advice now so I can try to avoid the upcoming surgeries.
    Reply: #61
  11. Kerry Merritt Team Diet Doctor

    I would consider myself a FASTING expert. I read all your books in 2018 and started fasting on and off. I have done many fasting cycles including a 21 day fast and a 19 day fast along with many 3–5-day fasts. I have even completed 3 times a 60-day OMAD in 2019, 2020 and 2021. At the end of 2021, I lost 67 pounds, I have a total of 100+ pounds to lose but in January 2022-April 2022 I was NOT as strict with my sugar intake or my fasting regiment therefore in April 2022 I woke up in pain and was severely sick. After going to the emergency hospital 3 times, tests revealed I had an infection in my ovaries, stones in my gallbladder, Fibroids, and the worst one, very high protein in my kidneys. I spent 8 days in hospital on IV Antibiotics and then sent home on antibiotics for 2 weeks. To this day my ovaries are still infected, which my OBGYN wants to remove, I still have the stones and fibroids although I do NOT have pain from them but the protein in my kidneys is extremely dangerously high (Albumin/Creatinine highest was 141.1 and most recently it is 75.9 mg/mmol), which doctor wants to do a biopsy on my kidneys. So, I am now on a list to have my ovaries removed, Gallstones removed and a Kidney biopsy, which I do NOT want to do and believe if I had the correct doctor all my issues would go away with fasting.
    I have been told by a Naturopath and a doctor that they think all of my issues stem from all the fasting I have done over the years. I do NOT believe that because I felt the healthiest when fasting after losing weight.
    Since you are a Nephrologist and understand the significance of fasting for health, I was hoping you could provide some guidance. I asked my doctor to send a referral to The Metabolic Clinic for me and she has but there is an 8-9 month waiting list. I am most concerned with my kidneys and I need your advice now so I can try to avoid the upcoming surgeries.

    Hi, Kellie! We are unable to provide medical advice here, but if you'd like to try to contact Dr. Fung, you can try his website. https://www.thefastingmethod.com/ We'd also recommend discussing any concerns with your primary physician.

1 2

Leave a reply

Reply to comment #0 by

Older posts