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Can intermittent fasting cure type 2 diabetes?

Patient standing on a scale
Written by Paul Taylor

Question:  I have type 2 diabetes and I’ve heard that intermittent fasting could cure me.  Is this true?

Answer:  In recent years, intermittent fasting has emerged as a novel way of treating patients with type 2 diabetes. There are anecdotal reports of patients who have lost weight, their blood sugar levels have improved significantly, and they no longer need to take their diabetes medications. Their disease appears to be in remission – if not exactly cured.

However, endocrinologists – the doctors who routinely treat diabetes – as well as dietitians, are skeptical.  They point to a lack of major studies that prove this approach is effective and safe long term.  After all, intermittent fasting requires a big change in eating habits and it remains to be seen how many people can stick with it.

The first thing you need to know is that there are different ways of doing intermittent fasting – which is basically not eating for certain periods of time.

For instance, you could restrict your consumption of food to just eight hours a day – say from 11 a.m. to 7 p.m. – and eat nothing else for the other 16 hours.

Or, you might have just one meal a day and then fast for 24 hours.

Another approach is to eat normally on some days of the week, while significantly curbing calories on other days.

Fasting has been part of human culture for thousands of years.  Most of the major religions encourage their believers to restrict food intake during certain times.

But the use of fasting to treat diabetes is relatively new.

The idea has been popularized internationally by Dr. Jason Fung – a nephrologist (kidney specialist) at Scarborough Hospital and medical director of the Intensive Dietary Management Clinic in Toronto.

Through a series of books and YouTube videos, Dr. Fung has attracted loyal followers who are convinced he has the answer to their diabetes problems.

Dr. Fung says he decided to experiment with intermittent fasting because he was frustrated seeing so many diabetic patients with kidney failure. “It occurred to me that fasting was an underutilized therapeutic option for losing weight,” he recalls. “I started doing this five years ago, and a lot of people got incredibly good results – it reversed their diabetes.”

Type 2 is the most common form of diabetes accounting for 85 to 90 per cent of cases. It usually develops later in life and it’s often associated with being overweight.

A major feature of the disease is a condition known as insulin resistance.  Insulin is a hormone that moves glucose (sugar), from the bloodstream into the body’s cells where it is used for energy.  For a variety of reasons that are not fully understood, the body’s tissues don’t respond adequately to insulin and glucose then becomes elevated in the bloodstream.

Poorly controlled blood-sugar levels can lead to a host of medical complications, increasing the risk of heart attack, stroke, kidney failure, blindness and limb amputation.

Diabetes is often treated with medications to make the body more responsive to insulin. Some patients also take additional insulin to top up the amount produced by their own bodies.

Dr. Fung believes the medical community “has been treating type 2 diabetes incorrectly.” In particular, he argues, that the medications used to clear sugar from the bloodstream end up overstuffing cells with glucose, which gets turned into fat. “Even if your blood-sugar gets better, you gain weight and your diabetes is only getting worse.”

According to Dr. Fung, cells are insulin resistant because they are already filled to the maximum with glucose. He compares insulin resistance to a suitcase that’s packed full of clothes. You can’t get more clothes in without taking some out, he explains.

“Periods of fasting allow the body to burn off the excess sugar and then the cells become responsive to the insulin once again.”

He also encourages patients to modify their diets, by cutting back on refined carbohydrates – such as bread and pasta made from white flour – which the body quickly converts into glucose and by adding healthy fats found in avocadoes, nuts and olive oil.

Once glucose stores are depleted, which happens after prolonged fasting, the body shifts to burning fat for fuel.

By fasting regularly, he says, patients tend to lose weight, their insulin resistance is overcome, and they can cut back or even stop taking their diabetes medications.

“Type 2 Diabetes is an entirely reversible disease,” he insists, challenging the traditional notion that’s a chronic and often progressive condition.

Despite his unconventional views, Dr. Fung is winning some converts in the medical profession. “It’s not for everybody, but if someone is motivated, it sure makes sense as a way to lose weight,” says Dr. Martin Strauss, a cardiologist at North York General Hospital.

Over the past two years, Dr. Strauss, who is also an assistant professor at the University of Toronto, says he has referred about 50 patients to Dr. Fung for treatment.  “I would say 30 to 40 per cent of them stick with it.”

Dr. Fung agrees that not everyone will succeed at intermittent fasting. He also notes that patients need medical supervision – especially if they are taking diabetes medications.  The doses of their drugs will likely need to be adjusted over time.

He says patients with diabetes should at least give it a try. “If you don’t like it, or you feel unwell, you can stop immediately.”

But most doctors are unlikely to recommend intermittent fasting without more scientific evidence that it can produce lasting results.

“We need a proper study with enough patients for a long duration of time to really prove whether this is safe and effective – or harmful,” says Dr. Jeremy Gilbert, an endocrinologist at Sunnybrook Health Sciences Centre in Toronto.

“All diets work in the short-term, but it’s the maintenance phase that’s so difficult,” he says.

There is a risk that those who attempt it and fail could end up worse off, speculates Annie Hoang, a registered dietitian at Sunnybrook. An individual’s metabolism might switch into “starvation mode,” reducing the amount of energy needed at rest, she explains.  That means some patients could regain all the weight they lost – and more – if they stop doing intermittent fasting.

Dr. Fung argues that won’t happen.

Whatever the case, Dr. Gilbert says, “this diet has some extreme components some of which makes sense, but it’s not clear how many people can actually do what he (Dr. Fung) is recommending indefinitely.”

Dr. Fung says he has personally treated more than a thousand patients over the past five years “with many of them sustaining their non-diabetic status over the duration.”

But he has not yet published in a peer-reviewed journal the data showing his patients’ actual rate of success.

“Intermittent fasting is not something I would necessarily recommend until we know more,” says Dr. Nicola Guess, a lecturer and nutrition researcher at King’s College London.






About the author


Paul Taylor

Paul Taylor retired from his role as Sunnybrook's Patient Navigation Advisor in 2020. From 2013 to 2020, he wrote a regular column in which he provided advice and answered questions from patients and their families. Follow Paul on Twitter @epaultaylor