Can yo-yo dieting break people’s metabolism?

Ask Dr. Jason Fung

There are tons of questions about intermittent fasting, like these:

  • If you’ve been yo-yo dieting your whole life, and you try fasting without losing much weight, is it hopeless? Is the metabolism broken?
  • Can weight loss lead to sagging skin, and if so what do you do about it?

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:

Broken Metabolism?

I am 51 years old. I have yo-yo dieted all my life. I think I have broken my metabolism! The fact that I am premenopausal does not help much.

I am trying the fasting, with a feeding window of five hours. I eat between 3 PM and 8 PM. I will have a little bit of coconut oil in my coffee in the a.m., and some bone broth if I am hungry in the afternoon. That is it. Before 3:00 pm.

I am not losing weight. My question is: what is wrong with me? I have tried every diet! Literally! If I stick with this, will the weight start to come off?

I have been trying this way for about a week now. I woke up this morning and I was actually up half a pound.

Any advice would be greatly appreciated!

Thank you,

Dr. Jason Fung:

Two possible changes. You can change to a classic water-only fast.

Second, you could try to extend the fasting longer. In our clinic, we typically use 24 hour fasts as the lowest level, and go up from there.

Regarding broken metabolism, see this post:

How to Fix Your Broken Metabolism by Doing the Exact Opposite

Sagging Skin

Hello Dr. Fung, thank you so much for taking questions!

In two previous queries, people asked about sagging skin with fasting. Are you saying that excessive sagging rarely or minimally occurs even with the relatively advanced ages of your patients? I sure hope so.

I have lost 80 pounds over the last two years and the hideous sagging around my neck makes me wonder whether it will be worth it to lose the remaining 60 pounds. I would look 100 years old at least! ?

I have fasted 55 days (in two to three day segments) since the beginning of the year. If I fast even more strictly, water only if necessary, is there likelihood that the sagging would be reversed? Does that actually happen often enough for it to be likely?


Dr. Jason Fung:

I can’t say for sure. We have had several patients lose over 100 pounds without the problems with sagging skin.

Remember, this is excess connective tissue (protein) that needs to be removed and fasting helps catabolize this protein. I can’t guarantee it will work, but water only fasting sounds like it would work better.


Hi Dr. Fung,

Thanks for all of the great info. I am obese (102 kg (225 lbs.) and 172 cm). I have fibromyalgia, lots of intolerances and other digestive issues. I am interested in fasting for a couple of weeks, or more depending how it goes.

I am really keen to experience autophagy and see if it helps me.

I note that on the “Intensive dietary Management” site you state in your blog that autophagy can be turned off by proteins and amino acids.

In another blog post you mention that most of the patients that fast with you are able to consume bone broth. In that post you provide a link to the “Paleo Leap” site which advises that bone broth contains proteins and amino acids.

My question: If during my fast I consume bone broth is it likely to turn off autophagy?

Thanks very much for your help. ?

Dr. Jason Fung:

Yes, it is likely bone broth will turn it off.

We use it in longer fasts to encourage compliance in our clinic, which is mostly focused on obesity and type 2 diabetes, rather than the theoretical benefits of autophagy.

If autophagy is your primary goal, then water only fasting and protein restriction would be more beneficial. See Dr. Rosdale’s presentation on this site:



Intermittent Fasting for Beginners

More questions and answers

Many more questions and answers:

Intermittent Fasting Q&A

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

The Obesity Code

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Full IF Course >


  1. Jacq
    Cheryl's question could have been written by me. After years of unsuccessful yo-yo dieting, I too feel "broken". Today's wake-up call is a blood glucose reading indicting pre-diabetes. About to try fasting and LCHF, but feeling very defeated.
  2. Lonnie
    HI Jacq, I have been a foodie my whole life. Type 2 by 42. I'm now 50 and have lost nearly 30kgs. It's not easy but it's so much easier than the Low GI diet that I was told to follow. I'm rarely ever hungry and have to force myself to eat some days. Fasting feels amazing - so much energy and clarity. I've gone from groaning when I stand from sitting in a chair to playing on the ground with my grandson and jumping up from the ground without a 2nd thought. So amazing to have full use of my body again. No IBS, no diabetic meds anymore, no psoriasis, dandruff. Everything works better and I didn't even exercise.

    I have bad days, weeks but I now have the tools to get back on track quickly. All my bloodwork have shown that Cholesterol is perfect, H1ac = 5.7%, Vitamin D normal (this was always low). Blood pressure good. Win Win Win.

    I hope I get to see my grandchildren grow up and I can be the inspirational active Grannie and not a old, fat and sick one.

  3. gilmore l. anfone
    sir, good day ! i am a diabetic and iam confused about drinking highfat milk. I read some articles about milk are high in sugar yet it is advice that said milk is good for diabetics. iam confused.

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