Diet & Weight Magazine

Long Fasts, Ketoacidosis and Weight Regain

By Dietdoctor @DietDoctor1
Long Fasts, Ketoacidosis and Weight Regain

There are tons of questions about intermittent fasting. Should you expect to regain some of the weight loss after breaking a long fast? Also, ketones tend to go up during longer fasts - is there a risk of ketoacidosis?

Dr. Jason Fung is one of the world's leading experts on fasting for weight loss or diabetes reversal. Here are a his answers to those questions and more:

Fasting, ketoacidosis and weight regain

I'm not diabetic and I'm not on any medications. I'm now 5.5 days into my 7-day fast and I feel great! I've been monitoring my blood sugar and ketone levels every 12 hours. Over the 5.5 days my blood sugar average is 81 and my ketone average is 4.1. This morning my blood sugar was 66 and ketones 5.4. I don't think I should be concerned about ketoacidosis but I can't help it, as my ketones get progressively higher I can't stop thinking about it. Please put my concerns to rest...

Is there any risk of my ketones going too high if I'm NOT a type 1 diabetic? I have been at a weight loss plateau for months even while eating strict LCHF and following a 16:8 eating plan. In the 5.5 days of fasting I'm down 7 lbs! In your weight loss management program, do you find clients are able to keep the weight off (after a long fast) when going back to an LCHF eating plan?
Thank you so much!!!!

Ketoacidosis mostly happens in type 1. Ketones are supposed to go up during fasting - it's called starvation ketosis.

There will usually be some weight regain after the fast, so be prepared. Generally, you can expect to lose 1/2 pound per day of fasting on average. For 7 days, that's 3 1/2 pounds. Everything else could be water weight which will come back, and it would still be OK. It doesn't mean the fast didn't work.
Dr. Jason Fung

Very low blood sugar

Hello Dr. Fung,
I just started fasting after reading your blog post series. I've never tested blood glucose before and thought I'd try it with this fast and just bought a meter. I know you can't give specific medical advice, but could you tell me from your experience with your patients...Do you feel a blood glucose reading of 39 on Day 3 of a fast falls within acceptable levels or do you feel that is too low? I have no symptoms and feel fine.


If you are taking diabetes medications then yes, it is too low. If not, the main thing is to make sure you are feeling well.

Dr. Jason Fung

Higher blood glucose when fasting

Hi Dr. Fung,
I was diagnosed with type 2 a month ago. my fasting glucose was 386. I started fasting and LCHF and now a little less then a month later my average number is 115! My Dr. wanted to put me on medication and I said no I will try this 🙂 So glad I found your Youtube video! I am wondering why sometimes when I fast for 34-48 hours my glucose is actually higher then on days I am eating?


Dr. Jason Fung: This is similar to the Dawn Phenomenon, Read my post here -

Dr. Jason Fung

More Questions and Answers

Many more questions and answers:

Intermittent Fasting Q&A

Read all earlier questions and answers - and ask your own! - here if you are a member:

Ask Jason Fung about intermittent fasting and type 2 diabetes - for members ( free trial available)

Read Dr. Jason Fung's new great book The Obesity Code for many more insights:

Long Fasts, Ketoacidosis and Weight Regain

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