Dr Michael Mosley reveals new fasting diet tips in latest book The Fast 800

It began as a revelation — eat whatever you want for five days and fast hard for two. But the man behind intermittent fasting has refined his theory … and Dr Michael Mosley argues there’s a magic number of calories that will see the fat just fall off.

At first, Dr Michael Mosley called it the 5:2, the diet that let you eat normally five days a week — but then hit you with some serious fasting on the two other days, with just 500 calories for women and 600 for men.

In The Fast Diet, a book he published in 2012 with journalist Mimi Spencer, the British doctor and science journalist laid out the principles and health benefits of what was then a very novel way of dieting called “intermittent fasting”.

It became an international bestseller, but Mosley has now refined his recommendations, as new scientific studies have become available.

He’d become interested in intermittent fasting when he set out to find a drug-free cure for his surprise diagnosis of Type 2 diabetes, a condition that can spawn a range of illnesses from blindness to limb amputations and kidney failure.

Using the 5:2, he lost 9kg and got his blood sugars back to normal, without medication — a remarkable outcome.

He was later told that new research from Professor Roy Taylor, a diabetes specialist at Newcastle University in the UK, suggested his success against diabetes was thanks to losing a lot of weight quickly — because losing 10 per cent of your body weight sees the fat drained from the liver and pancreas, helping restore the body to health.

Dr Michael Mosley

That led to another book, The 8-Week Blood Sugar Diet, which showed people with diabetes how to follow a rapid weight loss program, by cutting calorie intake to 800 a day.

The book also became an international bestseller.

So what’s new? Mosley says in his new book T he Fast 800 that the latest research has shown a rapid weight loss diet based on 800 calories a day can have big benefits even for people without diabetes.

The new program incorporates the 5:2, but is based on, among other things, more manageable 800-calorie fast days (equivalent to 3347 kilojoules). It is designed to provide a simple, effective way to shed fat and set yourself up for a healthier future.

The key, he writes, is 800.

“Eight hundred is the magic number when it comes to successful dieting — it’s high enough to be manageable and sustainable but low enough to trigger a range of desirable metabolic changes.

The choice you have to make is how intensively you want to do the program — i.e. how many 800-calorie days to include each week from the start, and how to adjust these as you progress.

“For rapid weight loss, as long as it is safe for you to do it, 800 calories a day, every day, is what you should be aiming at,” he says.

The Fast 800 book cover.

“This is a regimen that has been shown to be safely sustainable for weeks and months. You might want to take this approach if you have a lot of weight to lose; if you are in a hurry; if you have pre-diabetes or type 2 diabetes; if you have a fatty liver; if you want to kick your weight loss journey off with a bang; or perhaps because you have hit a weight loss plateau.

“On 800 calories a day you can expect to lose up to 5kg after two weeks, 9kg after four weeks and 14kg after eight weeks, most of which will be fat. Rapid weight loss is often described as ‘crash dieting’ but I want to show you how, done properly, it can be safely used.

“However, not everyone can or will want to stick to 800 calories a day for long. So after a few weeks of rapid weight loss, I suggest you consider switching to what I’m calling the ‘New 5:2’.

“The calorie amounts I came up with for the original Fast Diet — 500-600 calories twice a week — were based on human studies, but mainly on animal research. Effective though it is, some people found this approach a bit too tough. So I now recommend cutting to 800 calories twice a week. Will you still lose weight, fast? Yes, particularly if you start with the rapid weight loss approach, and then move to the New 5:2.”

An example of the meals in The Fast 800. Picture: Supplied.

So what does 800 calories a day look like?

Mosley’s new book has recipes as well, based on a low-carbohydrate Mediterranean diet that he says will help maintain muscle mass, stop the body’s metabolic rate from crashing as the weight reduces, and make it easier to keep weight off in the long-term.

Another key element of the book is the focus on keeping eating within limited times, “a relatively new form of intermittent fasting called Time Restricted Eating (TRE).”

“TRE has taken the internet by storm, particularly among the body-conscious under-30s,” Mosley writes. “It involves eating all your calories within a relatively narrow time window each day, usually 8 to 12 hours. This extends the length of your normal overnight fast (the time when you are asleep and not eating) and gives your body an opportunity to burn fat and do essential repairs. TRE is not an alternative to the 5:2; rather, it complements it.”

The book says studies have shown that if you are overweight or obese, losing 5 per cent of your body weight will:

■ Reduce your blood pressure and levels of blood fats (triglycerides), significantly cutting your risk of a heart attack or stroke.

■ Lower your risk of getting cancer. Carrying too much fat in the body leads to the release of hormones and inflammatory agents that boost cancer. Cancers linked to being overweight or obese, include two of the commonest: breast and bowel cancer.

■ Sleep better. When you put on weight it not only goes around your belly, but also around your neck. A fat neck means you are more likely to snore (which will keep your partner awake), and also far more likely to develop obstructive sleep apnoea, a disorder which causes people to stop breathing while sleeping. A 2014 study found that people who lost 5 per cent or more of their body weight got about 20 minutes more sleep, and it was better-quality sleep.

■ Cut your risk of developing type 2 diabetes. In one big study, people with pre-diabetes (raised blood sugars, not yet in the diabetic range) who lost more than 5 per cent of their body weight were 58 per cent less likely to develop type 2 diabetes than those who didn’t.

■ Boost your sex drive. Not just because you may feel more desirable but also because of hormonal changes and improved blood flow to the sex organs. ●

Edited extract from
The Fast 800 by
Dr Michael Mosley, published by Simon & Schuster Australia,
RRP $29.99.