Does fat cause type 2 diabetes?

Ask Dr. Jason Fung

  • Does fat cause type 2 diabetes?
  • How common is it that people reverse type 2 diabetes, using fasting and low carb, and over what period of time?
  • Should you use carb counting or glycemic index counting?

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

What proportion of patients at your clinic succeed in reversing diabetes, and over what period of time?

It would be interesting to have some reference points for people with different starting BMI’s and duration of diabetes – but any figures would be good: e.g. Of people with an initial BMI over 40 and diabetes over 10 years, x% had reversed it after 3 months, y% after 6 months and z% after 1 year.


It all depends on motivation and compliance. I don’t have hard numbers on compliance but my ballpark estimate is that only about half the patients in the clinic are compliant. Our Long Distance Program has much higher compliance, maybe 60-70%.

People who are not complying, i.e. they are not really following the program, have little chance of benefit. Of those that comply, I would estimate that 80% show improvement in their type 2 diabetes. However, to get complete reversal often takes years or more. The disease of type 2 diabetes takes decades or more to develop and does not go away fully in 2 weeks. That’s only wishful thinking. Also, if you return to the diet that gave you type 2 diabetes, the disease will return.

The most important factors in how long it takes is how severe your type 2 diabetes is, and how long you’ve had it (along with compliance). If you fast once or twice a week for 24 hours, it could take many years to fully reverse, if ever. If you do repeated, prolonged fasts, it may happen sooner. Doing a low-carb diet between fasts will also speed things up.

But the bottom line is this – if you don’t eat, yes, you will lose weight and reduce your blood sugars in type 2 diabetes. It is almost 100% effective.

Dr. Jason Fung

Learn more:

Does fat cause type 2 diabetes?

I am currently using this site for recipes; I have been addicted to sugar, mother died from kidney failure as a result of diabetes, father is following the same path (has diabetes, on dialysis). When I am on LCHF diet I feel great, clear, no fog, depression is less of an issue, and I have energy.

Along comes this link I get:

I understand that in addition to research, you have hundreds of people to use as clinical evidence against this. Where in this article are they going wrong science-wise? Is there something I should be aware of regarding fat and type 2 diabetes?


I do not believe that dietary fat causes type 2 diabetes. The proof is in the pudding. We’ve followed the advice to lower dietary fat and type 2 diabetes prevalence has increased dramatically. Common sense alone would tell us that this theory is likely untrue.

In this video, the doctor is correct in saying that fat found within muscle causes insulin resistance (fatty muscle). However, this ‘fatty muscle’ is not caused by EATING dietary fat. Instead eating refined carbohydrates and high insulin levels causes de novo lipogenesis in the liver which is exported to the muscles as VLDL and causes ‘fatty muscle’.

This same effect is seen in cattle where cows are fed high starch grain to cause ‘marbling’ of the beef, which is nothing more than ‘fatty muscle’. But it’s important to note that eating too many CARBS, not FAT causes this ‘fatty muscle’.

Dr. Jason Fung

Carb counting or glycemic index counting?

Hello Dr. Jason!

Is it the amount of carbs that plays a role or the glycemic index of the meal? If the second, maybe a cake full of fiber and low glycemic index sugar like coconut sugar could have lower glycemic index than a steak? Maybe carbophobia is not the optimum diet and carbs with low glycemic index are fine, even if the amount of carbs is high? Thanks!


In my opinion, it’s not carbs or glycemic index that causes obesity. Instead it’s the insulin response that is important. Therefore, I don’t think that carb counting or glycemic index captures what is most important.

Instead, it would be more useful to look at an ‘insulin index’. Marty Kendall at has done some excellent work in this area and estimates the insulin effect of foods as the net carbs (carbs minus fibre) plus half of protein.

It is important to understand that one can eat large amounts of carbohydrates and still have a small insulin effect, as proven by the Kitavan studies of Dr. Lindeberg. Carbohydrates are an important factor in the insulin response, but not the only effect – vinegar, fibre, dietary fat, protein, incretin effect and insulin resistance all play a role in determining the insulin response.

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 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.


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