Why could I eat what I wanted before and not gain weight?

Ask Dr. Jason Fung

Why can many people eat pizza, cola, pasta and almost everything they want in their teens… and suddenly in their late 20’s they put on weight just by looking at them?

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

Glucose response after diabetes reversal?

I am doing very well with fasting, but refuse to test my glucose tolerance until after I reach my goal. That said, I can’t find the answer to the following question anywhere on your website, or the Diet Doctor website…

When you reverse your diabetes, is there a possibility to have a “normal person’s” response again to a large dose of glucose? I know my long term goal is to keep fasting as a part of my lifestyle, but I would love to be able to have a normal meal with my family on vacation (for example).


Yes, you can have a normal meal with your family. It may be necessary to increase fasting after your vacation, though. Consider the sugar bowl analogy. Your body is like a sugar bowl. Over several decades, the cells of your body fill up with sugar, like the bowl. Once full, any sugar you eat overflows into the blood. That’s essentially insulin resistance. The normal amount of insulin can no longer force sugar into the cells because they are already full. It’s an overflow phenomenon.

When you reverse T2D, most people only do enough to no longer spill sugar into the blood, but the bowl is not empty. It’s simply not overflowing. So going back to a ‘normal’ diet, you will quickly spill sugar and the T2D is back. But the process of insulin resistance and overflow is the same. This is why so many people say that T2D is not curable. If you really wanted to empty the bowl, it could mean fasting every other day for 5 or 10 years to reverse the 20-30 years that preceded it.

Dr. Jason Fung

Why could I eat what I wanted before?


I was wondering why I could eat pizza, Cola, pasta and almost everything I wanted in my teens… and suddenly in my late 20’s I put on weight just by looking at them?


Because all that Cola and pasta was causing fatty liver and insulin resistance without you noticing it. Again, going back to the sugar bowl analogy, the cells of your body are filling up with sugar, but you don’t notice it. Once it starts to overflow, you get insulin resistance, fatty liver and the same pizza and Cola now get turned directly into fat.

Dr. Jason Fung

Learn more about insulin resistance and how to reverse it: A New Paradigm of Insulin Resistance

Possible to not lose any weight during extended fast?

End of day 3 of fasting, and no weight loss at all. I’ve had coffee, hot tea, water and broth. I feel great and no problems, so I’m not tempted to give up, but will hang in there. But… how no weight loss, and how only light ketosis?


I’ve seen it too, because the body weight is a poor measure of what’s happening. Usually we see waist circumference drop, and the weight stay stable, which means that you are losing visceral fat (the most dangerous kind) and perhaps gaining some lean mass due to increased growth hormone.

Ketosis is different. In some people, ketones don’t rise as quickly as glucose falls. Fasting usually will make the body more efficient at producing ketones, so it just takes the body some time to acclimate.

Dr. Jason Fung



Intermittent Fasting for Beginners

How to Reverse Type 2 Diabetes – The Quick Start Guide

Earlier Q&A sessions with Dr. Fung:

Many more questions and answers:

Intermittent Fasting Q&A

Q&A videos

  • Is low carb bad for exercise?
  • Is low carb bad for the kidneys?
  • Everything in moderation?

Top Dr. Fung videos

  • Diet Doctor Podcast #64 with Jason Fung
  • Part 8 of Dr. Jason Fung's diabetes course
    The essential problem with type 2 diabetes

More with Dr. Fung

Dr. Fung has his own blog at intensivedietarymanagement.com. He is also active on Twitter.

His book The Obesity Code is available on Amazon.

The Obesity Code

His new book, The Complete Guide to Fasting is also available on Amazon.


One comment

  1. Valerie
    Hi Rebecca,
    You're probably gaining water weight while losing fat (and muscle) during your extended fast. Also, if you drink lots of calories in your coffee and broth, you won't tap into your fat reserve.

    Growth hormone might prime your body to build muscle when you start eating again, but it won't increase your lean mass on its own while you fast (where would the building blocks come from?).

    Broth could be the culprit for the low ketosis.

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