“How can I lose weight when no diets are working?”

Ask Dr. Jason Fung

Does intermittent fasting help with uncontrolled blood sugar levels? Is vomiting during a fast okay? What could feeling cold when fasting mean? And, what can one do when nothing is working for weight loss?

It’s time for this week’s Q&A about intermittent fasting and low carb with Dr. Jason Fung:

HIGH blood sugars while fasting and LCHF diet

  1. Is it possible that intermittent fasting is not good for some diabetics with uncontrolled blood sugars?
  2. Is it more important to get on a new medication to control these high numbers than it is to “wait it out” with diet and IF alone?


  1. Intermittent fasting usually lowers blood sugars, but the effect is variable. In some cases, it goes down quickly, and others very slowly.
  2. Questions regarding medications can only be addressed by your own physician.

Dr. Jason Fung

Nausea and vomiting

Is vomiting during a prolonged fasting period normal?


No, vomiting is not normal during fasting. You can be hungry, but should not be vomiting. You should stop and seek medical advice.

Dr. Jason Fung

Core body temperature dropping during a fast

Should otherwise healthy people generally stop a ‘fast’ if they notice this coldness occurring and/ or can track a small body temperature change of up to .2 degrees below their normal temperature range during fasting?


Feeling cold is a sign of lowered basal metabolism. It would be important to revisit your dietary regimen to see if anything can be optimized. That may include stopping the fasting.

Dr. Jason Fung

Tests and best way to start

Do you have any recommendations for losing weight if keto and other diets don’t work? As to how to start and what tests that could be run, and continue to run, as well as target test results?


Try intermittent or extended fasting. Blood tests would be at the discretion of your own physician.

Dr. Jason Fung



Q&A videos

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  1. Shirley
    Although I am struggling with the weight lost I have not given up. I know the next best thing for me will be intermittent fasting. In-the-meantime I can proudly say so far LCHF has been beneficial in improving my overall Health. At age 63 my mental clarity has improved, my blood pressure is near normal and the blood pressure medication I was on, has been significantly reduced, I no longer get dizzy spells or palpitations. My eye sight has improved to the point the costly prescription glasses I carry with me are purely out of habit. I past my driving eyesight test with flying colors. Diet Doctor LCHF and Dr Fung's explanations of the affects of insulin in our body, has answered the question that nagged me for sometime. Why? when I ate certain foods? I ended up lacking in energy and feeling tired. Cheers! Diet Doctor you are the Best Prescription ever out there for me.
  2. April
    Thank You for that information
  3. Edwidge Jean
    Yes my name edwidge l want to loose weight i can't because I m thyroid hormone problems what I can do.
    Reply: #6
  4. Peter
    I've worked intermittent fasting into my weekly routine for five months now. Two 24 hour fasts per week on days of light exercise, and two more days of 6-hour food windows.

    My waist is the smallest it has been in over twenty years. Moreover, I've gotten stronger, since most of my exercise focuses on resistance training.

    The best part ofintermittent fasting is that a no longer worry about calories. I avoid alcohol and food that cause an insulin spike. Otherwise, I eat what I want to eat.

  5. John
    No mention of the question in the headline... Clickbait nonsense.
    Reply: #8
  6. Kristin Parker Team Diet Doctor

    Yes my name edwidge l want to loose weight i can't because I m thyroid hormone problems what I can do.

    You can eat keto/lchf with thyroid issues! Here is a link to our getting started challenge.

  7. James
    I can attest to this. Was LCHF for a while with 16:8 IF, then hit a very long plateau. Love eating this way (who wants to give up steak?!!) So I re-read Dr Fung's book and decided I needed some longer fasts. Started adding 36hr and a few longer ones. The bam! Weight came off like magic! Do this if your struggling! You'll thank me (or I guess you'll thank Dr Fung lol)
  8. Debra Rose
    He replied to try intermittent fasting.

    No mention of the question in the headline... Clickbait nonsense.

  9. 1 comment removed
  10. Jan
    What kind of "dieting" is not working for you, Sagar? Many times Low Carb/High Fat + intermittent fasting must become a "way of life"--not a diet! You rid yourself of high-inflammatory foods, sugars and foods which spike insulin, preferably grains as well, and your weight AND health changes. Your cravings go away, you eat less and actually save money!
  11. Delisha
    I need some advice. I have osteoarthritis in both hips and it's no cartilage just bone on bone. I am in a lot of pain. I used to take steroids give by my dor.er doctor. Now I receive injections which give minimal relief. I need to lose weight in order to be able to push my surgery out for about 5 years. Do you have any suggestions?
    Reply: #15
  12. Carol
    Persevere wth LCHF. Lots of fat for the cells. Watch Dr Ken Berry on YouTube talk about arthritis.
  13. Laurie
    Headline does not match article contents.
  14. 1 comment removed
  15. Kristin Parker Team Diet Doctor
    Delisha, you can still eat keto/lchf. The injections may make it harder to lose weight, but you can still eat this way. Here's a link to our 2 week challenge to help you get started.

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