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Evidence Based

Dr. Jason Fung’s Fasting Methods

Dr. Jason Fung is a renowned expert on intermittent fasting and low carb diets, placing a focus on type 2 diabetes prevention. In this article we’re going to cover the core ideas of Dr. Jason Fung and present our take on them in the context of intermittent fasting.

What is intermittent fasting?

If you’ve heard of IF but have never fully understood its concept, it’s merely an eating pattern that cycles between periods of fasting and eating. There’s plenty of flexibility when it comes to practicing IF.

You are allowed to fast for as long or as short as you like. But obviously, for health reasons, longer fasts that last for more than a few days may require health supervision.

Here’s a short guide to some of the most popular eating patterns followed in IF: Short fasts (less than 24 hours)

  • 16:8 – You get in all your meals within 8 hours and fast for the remaining 16 hours. This pattern of IF is typically practiced daily, or almost daily.
  • 20:4 – You eat all your meals within 4 hours and fast for the remaining 20 hours. Those following this cycle tend to eat either one meal or two smaller meals during the feeding window.

Long fasts (more than 24 hours)

  • 24-hour – You can choose to fast from dinner to dinner, or from lunch to lunch. Basically, this method only allows you to eat once a day. Generally, this fasting pattern is incorporated two to three times a week.
  • 5:2 – You eat as per usual for five days and fast for two days. Don’t worry: you’ll not starve on your fasting days – you’re allowed to eat 500 calories each day.
  • Alternate-day – You practice fasting days where you are only allowed 500 calories daily, every alternate day.

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IF: Solution for Weight Loss?

Part of the reason for IF’s widespread acceptance in recent years can be attributed to Dr. Jason Fung’s fasting book – The Obesity Code: Unlocking the Secrets of Weight Loss.

As can be surmised from the title of his book, Dr. Jason Fung is sure that he’s found the secret to sustainable weight loss: intermittent fasting. How come?

Well, it’s all because of a hormone – insulin. He believes that sustainable weight loss can only be achieved when insulin is lowered. Or in other words – when you’re practicing IF.

It’s all about insulin

Given that Dr. Jason Fung has based his entire argument on insulin, we think it’s prime time for us to examine what this hormone really is, and the roles it plays in your body. So – what is insulin?

Insulin is a hormone that enables your body to absorb the sugar in your blood, obtained from the carbohydrates in the food you eat, into your cells for energy. When you have more sugar in your body than it needs, insulin stores the excess amount in your liver and releases it when your blood sugar levels drop, or when you need more sugar.

Insulin is, therefore, a hormone that helps balance out your blood sugar levels and ensures that it stays within a healthy range.

What is the basis of Jason Fung’s fasting argument?

The entire basis behind Dr. Jason Fung’s intermittent fasting idea is that the body exists only in two states – the fed (high insulin levels) and the fasted (low insulin levels) state. He argues that when insulin levels are high, we’re continually storing food energy, and therefore, fat in our liver and body parts.

On the contrary, when insulin levels are low, he proposes that the body then switches to burning energy stores. Intermittent fasting, in his eyes, enables the body to use its stored energy when insulin levels are low.

Ultimately, he proposes that if you follow a regular eating pattern, your body is continuously overwhelmed by high levels of insulin – it does not burn body fat. This has led to his argument that you’ll lose weight when you lower your insulin levels (typically achieved through the fasting period during IF).

What does Jason Fung say about long term fasting (more than 36 hours)?

While he believes that longer fasting periods can lead to swifter results. But, Dr. Jason Fung advises caution when it comes to extending non-eating periods. He cautions that as you progressively go longer without food consumption, the risk of complications increases.

Also, he discourages people from fasting for more than 14 days; such a long period of fasting can lead to refeeding syndrome – a dangerous shift in fluids and minerals that might occur when food is re-introduced after a long fast. Dr. Jason Fung instructs for anyone who feels unwell at any point in the diet to stop.

Also, he mentions that those on medications should never try out long fasting periods without first clearing their intentions with their doctor. Obviously, expounding on his advice, you should never follow the methods of Jason Fung’s fasting when ill.

Does science support intermittent fasting?

When you think about it, Dr. Jason Fung’s intermittent fasting argument sounds fair and reasonable. But – does current scientific literature support his view?

Spoiler alert: the answer is yes. Scientific research also investigates other health benefits it has.

Enhances weight loss

Turns out, Dr. Jason Fung is right, time-restricted eating can help you lose and keep the weight off. This is extremely heartening to hear, given that many of those who try their hands at intermittent fasting do it to lose weight.

If you’ve been paying attention, you’d know that intermittent fasting regulates the levels of insulin in your body; with lower amounts of the hormone in your body, the breakdown of your body fat is enhanced. Research supports this hypothesis: in fact, short-term fasting has been found to increase metabolic rates by as much as 14%!

As you know, the more calories you burn, the more weight you lose. Ultimately, current research supports Dr. Jason Fung’s idea that intermittent fasting is an incredibly effective tool for weight and fat loss.

Lowers risk of type 2 diabetes

Type 2 diabetes – a chronic condition which features insulin resistance – has become increasingly common in recent decades.

Now, what is insulin resistance? It’s a term given to a process when cells in the body don’t respond appropriately to insulin. As a result, glucose is more likely to build up in the blood, and this can eventually lead to overly-high blood sugar levels (type 2 diabetes). Thus, anything that minimizes insulin resistance can help lower blood sugar levels and circumvent type 2 diabetes.

And this is where intermittent fasting comes in; the diet has managed to demonstrate significant benefits for insulin resistance, and lead to impressive reductions in blood glucose levels.

Studies on humans have shown that intermittent fasting can reduce fasting blood sugar by as much as 6%. And that’s not all; fasting insulin was also found to have been lowered by 20% to 31%!

What the above research findings imply is that time-restricted eating can reduce insulin resistance and lower blood sugar levels – both being incredibly helpful in protecting people from developing type 2 diabetes.

Fights inflammation

The development of severe, chronic conditions – such as heart disease, cancer, and rheumatoid arthritis – can be partly attributed to inflammation. And of course, when you decrease the levels of inflammation present in your body, you can achieve better health.

A study that involved 50 healthy adults found that the month-long practice of intermittent fasting significantly decreased levels of inflammatory markers in subjects. This effect was also replicated when people fasted for 12 hours daily over one month.

Promotes cardiovascular health

Heart disease accounts for nearly one-third of deaths globally; it can, therefore, be considered the leading cause of death. If you’ve always been worried that you’d be part of that statistics, you might want to try out intermittent fasting.

In fact, a small study found that just short eight weeks of alternate-day fasting can significantly reduce levels of “bad” LDL cholesterol and blood triglycerides.

Also, another more extensive study that involved 4629 people found that fasting is associated with a lower risk of coronary disease, as well as a significantly lower risk of diabetes – a major risk factor for heart disease.

Induces autophagy

Wait – autophagy? What’s that? Put simply, autophagy is the natural regeneration process that occurs at a cellular level in the body. It can help reduce the likelihood of contracting certain diseases, as well as prolonging lifespan.

And this is where one of the most exciting applications of time-restricted eating reveals itself: the extension of a person’s lifespan. Studies in rats have demonstrated that intermittent fasting can help them live longer.

How much longer, you ask? In one study, rats that fasted on alternate days lived 83% longer than rats who didn’t fast. Read that again: 83%! We can finally understand why intermittent fasting has grown its roots amongst the anti-aging crowd.

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Bottom Line

The current scientific literature supports Dr. Jason Fung’s hypothesis that sustained weight loss can be achieved through the mechanism of lowered insulin levels. And undoubtedly, it seems that intermittent fasting is the surest way to achieve this effect.

Furthermore, we find it heartening to see that fasting is also associated with a wide array of health benefits in addition to weight loss – blood sugar control, heart health, and possible lifespan extension.

Ultimately, intermittent fasting is a powerful tool you can use to stimulate your weight loss and improve your health. To take inspiration from the title of Dr. Jason Fung’s fasting book: we can safely say that he seems like he’s managed to unlock the secret to obesity.


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This is an evidence-based article that includes scientific citations. DoFasting’s professional writers and editors prepared the content, which a team of medical experts verified to be accurate.

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