Can fasting be dangerous?

Here’s a treat: Dr. Stephen Phinney, expert on ketogenic diets and performance, answers questions related to weight loss and health in the video above.

Dr. Phinney has a slightly more skeptical perspective on fasting than some other experts. Specifically, he worries about the results of extended fasting (more than 24 hours) on protein loss and the risk of re-feeding syndrome.

Personally, I think it’s clear that longer periods of fasting (over 24 hours) results in some loss of lean mass. However, the loss is way smaller than most people believe, and under most circumstances it’s simple to regain that lean mass between fasting periods. At least if you eat high-quality foods when you’re not fasting.

To listen to Dr. Phinney’s thoughts on fasting you can skip to 46 minutes into the video above.


Longer Fasting Regimens

Fasting and Re-Feeding Syndrome

Fasting and Muscle Mass

Intermittent Fasting for Beginners

Top videos with Dr. Phinney

  1. Run on Fat – Cereal Killers 2
  2. Low-carb living
  3. Low-carb living
  4. Low-carb ketogenic diets for athletes


  1. Gianni
    I am not a doctor, so I just talk as a someone who fasts weekly. I am not overwheight eather.
    I feel great when I fast and despite the fact I do LCHF diet, I think I would probably gain some weight without fasting. I am not worry about lean mass loss, since I excercise and the way I mentally and physically feel after a 24 hour fasting is amazing.
  2. Andy
    WARNING! Refeeding syndrome is not the only risk associated with fasting. I found this out the hard way. There is a reason why Dr. Jason Fung recommends clearing it with your doctor if you plan to fast longer than 24 hours or a 5:2 fast. THIS SHOULD BE A HIGHLY STRESSED WARNING!!! Heart attacks are another danger of fasting. On the night of Day 4 of a 7 Day fast, I had a heart attack and I have no medical problems, no diabetes, no heart disease, no history of heart attacks and this lipid profile: Lipids Test from 5/18/2015 (Fasted): Total Serum Cholesterol: 152, HDL: 41, LDL: 84, Triglycerides: 134, Glucose: 97. It is possibly due to a potassium deficiency. I ate 11 bananas the next day and am feeling a lot better. I am not going to attempt this again without my doctor's okay! DON'T PRETEND THERE ARE NO DANGERS!!!!
  3. 1 comment removed
  4. Lynn Turner
    My Dr. said I could do anything up to 5 days. He recommends that he supervise anything over 5 days. My personal opinion is everyone is different and Dr. supervision, at least initially, is best to fully understand the mechanics of an LCHF diet. I have lost 70 and counting and I am so grateful to the doctors running the program I participate in.
  5. bill
    Dr. E:

    Good on you for posting this video. We finally
    get another side to the issue from a well
    respected doctor, on your site.

    You have been excessively promoting fasting on
    this site and I think that may come around to
    bite you. There are many caveats regarding
    fasting as Andy above talks about. I highly
    recommend you go back to focusing on LCHF.

    Let the fasting advocates start their own blogs.

    Reply: #7
  6. gbl
    By watching this free video (I wouldn't have seen it otherwise) I learned why my ankles are always hugely swollen. Dr. Phinney discusses salt intake. I have always been no salt to low salt (doctor's advice) and have rarely eaten processed or packaged foods. I put Kosher salt on my food for two days now and drank salted (homemade) chicken broth and my ankles are bony slim, for the first time in a decade. Please do continue to put pivotal videos free. Many thanks Dr. Phinney, and the person who asked the questions near the end of the video.
  7. Clare
    I agree Bill.
    I think this is a bit of a dangerous fad. A day here or there may have benefits but this is rapidly becoming a competitive boasting thing and I find it worrying and wearisome in equal measure.

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