How fasting reverses type 2 diabetes


While many consider type 2 diabetes (T2D) irreversible, fasting has been long known to reverse diabetes. In a previous post, we considered bariatric surgery. While extreme, these surgeries have proven the point that the metabolic abnormalities that underlie T2D (hyperinsulinemia, insulin resistance) can be fully reversible even after a few short weeks.

Many early studies were done with the heavy-duty Roux-en-Y surgery, which is the heavyweight champions of surgeries. The best weight loss. The most complications.

surgerycuresdiabetes5But even milder forms of bariatric surgery show the same reversibility of T2D. A gastric band is essentially a belt implanted around your stomach. The surgeon keeps tightening the belt so that you can’t eat.

The results of gastric banding versus medical treatment showed a significant and pretty good drop in their fasting blood sugars. In other words, their T2D was reversing in a b-i-g way. Those given medicines alone basically stayed the same. They were no better than before.

Gastric banding a 500 pound patient will still reverse 20 years of diabesity within weeks. One of the main questions is why? There are many hypotheses, but essentially, it is likely the sudden severe restriction of all calories that causes this beneficial effect. I believe this is the same thing as the time tested, ancient healing tradition of fasting. Fasting is the voluntary restriction of food for religious, health, or other purposes (eg. hunger strikes). Is bariatrics simply a surgically enforced fast? I believe the answer is yes.

It’s not a progressive disease

fastingcuresdiabetes1The success of both bariatrics and fasting proves that T2D is not progressive and chronic. It’s in fact a fully reversible disease. Consider this real life example. A lady in her mid 60’s was injecting 120 units of insulin daily along with 2 grams/day of metformin (a type of medication used for T2D). She had T2D for 27 years and had been progressively using higher and higher doses of insulin in an effort to control her blood sugars. However, things were getting worse.

In desperation, she was referred to the Intensive Dietary Management Program. We started her on a regimen that included fasting under strict medical supervision. We started with a full week of fasting and immediately reduced her medications. When she was feeling well, she continued for a second week, then a third. By that time she was off her insulin. We then switched to a LCHF diet along with alternate daily fasting. It’s been over a year now, and she continues to be off all insulin and medications with a HbA1C of 5.9%. Technically, she is no longer diabetic (defined by an A1C of less than 6.4%).

fastingcuresdiabetes2She feels terrific – with more energy now than she has had for over a decade. Her husband was so impressed that he also started our program and has recently come off all his insulin, too.

But wait! The diabetes ‘experts’ insist that T2D was a chronic and progressive disease! How can this lady, with her 27 year history of T2D, suddenly reverse her disease and become non-diabetic? How can this possibly happen?

The answer is fasting

The answer is quite simple. The statement that T2D is chronic and progressive is wrong. The ‘experts’ were being economical with the truth.

But the fact that fasting reverses type 2 diabetes has been known for close to 100 years! One of the most famous diabetologists in the history of the world – Dr. Elliot Joslin wrote about it in the Canadian Medical Association Journal in 1916! In fact, he thought that it was so obvious that fasting was helpful that studies would not even be necessary. This, from the guy that Harvard University used to name its world famous Joslin Center for Diabetes.

What happened to Joslin and fasting for diabetes? Well, back then, medical science had not yet distinguished Type 1 and Type 2 diabetes back then. Fasting is not useful for type 1, and type 2 was still quite unusual back then. After the discovery of insulin in the early 1920’s, all the focus turned to it as the ‘cure’ for type 2 diabetes. While it was a major advance for type 1, it was not quite the panacea for type 2s. However, most of the interest in fasting disappeared as doctors focused on what would be their mantra for the next century – drugs, drugs, drugs. All types of dietary therapy fell into disrepute, since they were really not useful in type 1 diabetes, and have stayed there ever since.

fastingcuresdiabetes3The effect of wartime starvation on T2D also obviously highlights the effect of reducing food consumption on diabetes. During both world wars, the mortality from diabetes dropped precipitously. In the interwar period, as people went back to their accustomed eating habits, it went back up. This, of course, is quite easy to understand. Since T2D is essentially a disease of excessive sugar in the body, reducing intake of sugars and carbohydrates should cause less disease.

Bariatrics or fasting?

Returning to the point that bariatrics is simply a surgically enforced fast, you can directly compare the effects of fasting and bariatrics. One fascinating study assessed patients waiting for bariatric surgery who were given a period of fasting beforehand. The reasoning was that many morbidly obese patients had enormous fatty livers. If you could somehow reduce this fatty liver and reduce their weight somewhat, the risk of surgical complications would be reduced since there is now more room to work within the surgical field.

The reduction in liver size would make working in the abdominal cavity much easier, with better vision. Since many of these procedures are done laparascopically, being able to see better is a huge benefit. Also, with less abdominal distention, abdominal wound healing was significantly improved. Therefore, fasting before surgery makes total sense.

In the meantime, you could compare both sugar control and weight loss during the fasting period and also during the post surgical period. Since bariatrics is considered the heavy weight champ, this was a real David vs Goliath battle (Fasting vs Surgery).

In the graph below, you can see the results. In the first graph, fasting caused 7.3 kg weight loss compared to only 4 kg for surgery. The second graph shows the overall ‘glycemia’ or the total amount of sugar in the blood over the day. During fasting, there was far less sugar in the blood (1293 vs 1478). On both counts you can see that the fasting was actually significantly better than the surgery! Blood sugars came down faster, as did weight. David (fasting) beat Goliath (bariatric)!

fastingcuresdiabetes4If all the benefits of bariatric surgery accrue because of fasting, why not simply do the fasting and skip the surgery? The standard answer is that people cannot do the fasting without the surgical enforcement. But have they ever tried? How do you know that you cannot fast for an extended period of time if you have never tried it? Shouldn’t you at least give it a shot before giving up?

But my main point is again, not to criticize or praise surgery. Rather my point is this. Fasting reverses type 2 diabetes. Rather than the chronic and progressive disease that we have been promised, instead T2D turns out to be a treatable and reversible condition. Both practices of fasting and bariatric surgery prove the point. This is a curable disease. Type 2 diabetes is entirely reversible. This changes everything. A New Hope arises.

Jason Fung


Intermittent fasting for beginners


Video on how to do it

Therapeutic Fasting – Dr. Jason Fung
How to Reverse Diabetes Type 2 – Dr. Jason Fung


Popular videos about diabetes

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Earlier with Dr. Jason Fung

Obesity – Solving the Two-Compartment Problem

Why Fasting Is More Effective Than Calorie Counting

Fasting and Cholesterol

The Calorie Debacle

Fasting and Growth Hormone

The Complete Guide to Fasting Is Finally Available!

How Does Fasting Affect Your Brain?

How to Renew Your Body: Fasting and Autophagy

Complications of Diabetes – A Disease Affecting All Organs

How Much Protein Should You Eat?

Practical Tips for Fasting

The Common Currency in Our Bodies Is Not Calories – Guess What It Is?

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.



  1. Thiago
    After a long period of fasting could a diabetic follow paleo dieta Rich in startch vegetables, no startch vegetables, green leaf, fruits, Meat, ChicKen, fish, eggs?
  2. 1 comment removed
  3. Simon
    Mate, Gotta love the 100 year old Joslin ref... Gangsta!
  4. Eli Jordan
    Interesting for sure. I've done a few total fasts and more than a few fruits and vegetables fast. They would work but I'd put on wait as soon as I came off. I have an on and again off again relationship with Diets, just tried something recently called the 3 week diet. Read the review at and it seemed all right. We're see how it goes. Great Article Doctor Jung.
  5. Bea
    I am very obese and suddenly I had 280 morning blood sugar. I was never able to stick with a diet, plus I was eating in depressed phases, which I had often, and the result was that I was putting on more and more weight. Having gone from pre-diabetes to diabetes at 45 was a shocker, because several relatives had died of diabetes 2. It took me three months to get over the shock, means I ignored the problem. Then I asked for Metformin and started restricting my calories two days later while reducing carbs and increasing fat and protein. I started at 1000 calories, went to 800, then to 400. Metformin from 850 to 1700mg. I completed a full month by now, almost two weeks on 400 calories. I lost 13 kg within a month and my blood sugar is back to normal. I have yet to try out if it will stay that way when going off Metformin, but I'm pretty positive. I have to add that I was still pretty lazy about exercising and did not do very much besides once a week going for an extra walk of one hour. My lifestyle is still sedentary. I believe that the meds helped me have less hunger, and additionally plenty of diarrhea. Hunger was always a huge problem. But even more so eating out of habit. I do not feel really hungry now on 400 calories, nor do the usual situations trigger the usual urges without me being able to just shrug it off. I can go to sleep with a rumbling stomach now, without classifying it as hunger, and it happens very seldom and is over within minutes. I'm eating according to plan every day now but still eat what I feel like eating to keep myself enjoying food, even if not all of my 400 calories are perfectly healthy food. I feel a lot better already, like my belly was shrinking and now I can sleep on my back without feeling like suffocating, therefore I plan to continue my fasting, with sometimes adding in a refeed day of no more than normal calories, with loading up on carbs, which helps me regain energy and to give my weight loss a push when it stops. I never enjoyed fasting so much before in my life!
  6. Bea
    I have to add that I was morbidly obese for more than ten years now and many times I got surgery suggested. But I always said I want to make it on my own and not with a surgery everyone I knew had complications with, especially because I am a single mother. I failed many times at dieting and already gave up when I got the news that now I am truly the new owner of a shiny diabetes 2. I'm lucky to have become fully diabetic. I am truly thankful for my diabetes. The shock gave me the push I needed to finally do what is good for me, because I definitely did not want to fall as sick for years as my relatives did before dying from it. Most of all I did not want to go blind. And now I fast and it is all of a sudden unbelievably easy to eat just once or twice a day. I do not eat anything with artificial sweeteners. Instead I'm eating lots of fish and eggs and veggies and a little fruit to it as dessert. Food or drinks with added sugar taste now weird to horrible to me. Things can change really fast. I watched videos about reversing diabetes. I was scared of eating too many carbs, and I could not bring myself to eat raw. But high fat and protein with low carb works so easy for me.
  7. Jos
    Please read this: this says otherwise. Also Diabetes 2 is not irreversible, my docter said. If I loose enough weight, chances are my DB 2 is gone
  8. Ken Hooper
    Jos - I read the article you posted with regards to intermittent fasting suggesting that intermittent fasting may cause damage to the pancreas. There are a few salient points in this article and one of those points is that the findings have not been peer reviewed which is a critical step to the acceptability of any new findings. In general, the article comes out on the positive side with regards to intermittent fasting. Many people who have decided to follow the fasting route have been satisfied with the results including myself. The primary thing to remember is that intermittent fasting is not a diet, it's a lifestyle choice and it takes several forms. Dr. Fung as a principal proponent of this regime is a real doctor in Toronto and his specialty is nephrology and he has treated 1000s and has witnessed success in dealing with diabetic individuals by use of fasting. So there is a well documented track track record. His problem is that he usually sees diabetics when the damage has already been done to the kidneys. He can't undo the damage he can only mitigate it.
    In my particular case, I intermittent fast 18/6 or 17/7. I am154 lbs, 5'7". My A1C is normal and glucose readings are good. I lost 20 pounds after diagnosis in May of last year, and of course I became interested in all things diabetic and of course intermittent fasting came up. Like yourself, my doctor stated that diabetes is permanent because a person will always have a propensity for a diabetic condition, just as an alcoholic will always have a propensity for alcoholism. Diabetics and alcoholics simply have to avoid those things that create the problem. By September, of last year I was off the metformin, and I started IF shortly after. The idea behind IF is to give your pancreas a rest. As a Canadian we Canadians suffer from the same modern day proclivities as Americans in that we have the problems with rising obesity and the consequent health problems because of our approach to eating - breakfast, snack, lunch, snack, supper, snack, and finally, late night snack. I cut all of that out 17 to 18 hours a day and my pancreas are breathing a sigh of relief. I eat two fully nutrious meals a day and I maintain my weight. Our ancestors had shorter lifespans because of the presence of disease and infant and maternal mortality, but there were many who lived a long time. My ancestor who came to Canada in 1648 was born in 1617, and died in 1701. He probably ate two meals a day and I'm sure he never snacked because there was nothing to snack on as everything had to be prepared. Diabetes is a disease of the well fed which all goes show, there's no free lunch.
  9. 1 comment removed
  10. Doug R
    Your article is not clear if the lady fasted total fast nor if the 3 weeks were consecutive.
  11. Anthony
    What's the best way to find a doctor who can supervise a person with Type II Diabetes in fasting? My father would like to consider this approach to reversing his Diabetes, but would need support and supervision in the process because he's on a slue of medications and I'm not finding doctors who support this method online.
    Reply: #12
  12. Kristin Parker Team Diet Doctor

    What's the best way to find a doctor who can supervise a person with Type II Diabetes in fasting? My father would like to consider this approach to reversing his Diabetes, but would need support and supervision in the process because he's on a slue of medications and I'm not finding doctors who support this method online.

    Here is our directory of low carb friendly physicians.

  13. salvador
    fasting 12 or 21 days i hop all you body runs better ,fasting is cheep .diabetes ? my not yet ,this year 40 days fasting ¨alex suvorin¨ book
    Reply: #14
  14. Kerry Merritt Team Diet Doctor

    fasting 12 or 21 days i hop all you body runs better ,fasting is cheep .diabetes ? my not yet ,this year 40 days fasting ¨alex suvorin¨ book

    Please keep in mind that we recommend a doctor's supervision for any fasts longer than 36 hours.

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