Can you really slim while you sleep? The hot new fasting diet

Published Tuesday, Apr 19 2016, 20:00 BST  |  By  |  Add comment
A controversial new book claims fasting overnight could be the key to losing weight. But can it really be that simple? We find out all you need to know...

Yes, you read that right... No more counting calories or totting up points, the latest diet book says you can lose weight while you sleep.

It almost sounds too good to be true, doesn't it? Yet the new book, The Obesity Code: Unlocking the Secrets Of Weight Loss by Dr Jason Fung, a physician and kidney specialist from Canada, claims when you eat is just as important as what you eat and by fasting over short periods of time – such as overnight – we could boost our chances of losing weight.

Can you really slim while you sleep?

© Sally Anscombe / Getty


For many of us, the idea of abstaining from eating food is terrifying, yet Dr Fung believes it's the key to losing weight successfully.

When we eat, the hormone insulin is released into our blood, with some sugar being used as energy and some stored in the liver for later use.

Once it's full, the excess sugar is stored as fat. When you stop eating, insulin levels fall and fat is burned for energy.

But due to modern eating patterns, including snacking regularly and eating late at night, our bodies often don't get the chance to burn off the fat stores – leading to high insulin levels and more storage of fat and sugar, making it is almost impossible to lose weight.

Dr Fung believes the only way to break this cycle is to abstain from food so your insulin levels drop and reset your hormone balance.

Sounds extreme, doesn't it? But here's the good bit. If you're not hugely overweight, fasting can simply mean skipping a meal or two and you can even do it in your sleep.


As you've guessed, it's not as easy as going to bed and waking up 7lb lighter. The aim is to balance our feeding and fasting periods, while sticking to a high natural fat, low-carb diet.

So start with a 12-14-hour fast.

Eat your dinner at 7pm and then eat nothing else until you have breakfast, around 7 or 8am the next day.

Then, try occasionally extending the gap between the two meals to 16 hours – skip breakfast, eat a healthy lunch, then stop eating again after you've had dinner.

It goes against everything we've been told about breakfast being the most important meal of the day, but Dr Fung says if you're not hungry when you wake, don't eat and just have lunch at 12pm.

If you have diabetes, a chronic condition or you are on medication, you must seek medical advice before fasting.


When fasting, you can drink coffee, tea, water and homemade broth – made from beef, pork, chicken or fish bones or vegetables – which keeps you hydrated while providing essential nutrients. Of course, that doesn't mean the rest of the time you can scoff whatever you want. All foods raise insulin levels to some degree, but sugar and carbohydrates are the worst offenders.

So cut out all added sugars – such as fizzy drinks and processed foods – and reduce your refined grains intake, including pasta and bread.

Eat natural fats, like butter and olive oil, and fill up on aubergine, kale, spinach, carrots, broccoli, peas and cauliflower, which all contain natural carbs. Protein should amount to 20-30 per cent of your total calories.


Even though snacks are banned, a bit of dark chocolate with more than 70 per cent cocoa should satisfy your sweet cravings. It does not naturally contain sugar and has significant amounts of fibre and antioxidants. Even better, you can also have a couple of glasses of red wine, as it doesn't raise insulin levels.


Drinking green tea can help you fast if you're trying to slim while you sleep

© Yuta Sekiguchi / EyeEm / Getty

Replace snacks with a cup of green tea

For so long we've been told that eating little and often is good for our metabolism, but Dr Fung says grazing all day constantly stimulates our insulin, making it harder to lose weight. Instead, try replacing your snacks with a cup of green tea, which works as an appetite suppressant.


By doing a 16-hour fast – from dinner to lunch – some days and at least 12-14 hours a night the rest, you could lose up to 4lb a week. Add in a 24-hour fast once or twice a week – eating dinner one day and not eating again until dinnertime the next day – to see a bigger weight loss.


When it comes to losing weight, Dr Fung says that it's 95 per cent diet and five per cent exercise, so instead focus on what and when you are eating. But as exercise does have lots of benefits, it's still good to keep active.


Boiled eggs can be eaten for breakfast if you're trying to slim while you sleep

© Rachel Husband / Getty

Start the day with two eggs

Breakfast foods often contain lots of sugar and carbohydrates, so start the day with two eggs, a sausage and an apple or a bowl of greek yoghurt and strawberries.

A rocket salad with walnuts, pear and goat's cheese is a great, healthy lunch.

At dinnertime, you could have halibut pan fried in butter and coconut oil, with steamed broccoli and kale.

Dr Fung suggests cutting out dessert completely, but you could have a bowl of berries and cherries with whipped cream.

The Obesity Code: Unlocking The Secrets Of Weight Loss by Jason Fung MD (Scribe UK), £14.99, out now

By Gemma Wilock

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