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Not only was everything he thought he knew about food turned on its head, he learned that all those years sweating in the gym have probably been a waste of time.
Dr Michael Mosley is the BBC science presenter credited with discovering the revolutionary 5:2 diet.
From his home in the English countryside, the father of four with a background in science and medicine is leading a revolution championing the surprising benefits of fasting.
“Before all this happened I looked at diets, I’d seen my father struggle with [diets]. He tried everything. And he failed at all of them. And so everything I had read told me that diets don’t work,” Dr Mosley said.
Michael didn’t set out to discover a diet.
He didn’t even think he had a weight problem.
As a child he was skinny, as an adult he was a little heavy around the middle but nothing to worry about, he thought.
His father, however, always struggled with his weight, and the problems that caused it.
“He died at the age of 73 and he was diabetic and he had heart failure, and he was going demented. He also had prostate cancer, so [it was] which ever was going to knock him off first,” Michael said.
“I went to see a doctor about something completely different. I was worried about a mole I had and she did routine blood test and she said, ‘I have some very bad news for you, you’re a diabetic, we’re going to have to put you on medication and your cholesterol is sky high at the moment’.”
Worried by the diagnosis, Dr Mosley went searching for solutions and, along the way, filmed his journey of discovery for the BBC.
To save his life – and have a healthy future – he first had to look back.
Michael’s own experience was that his well-fed lifestyle was harming his life expectancy.
During his documentary he put himself through a battery of tests.
“There’s a thing called metabolic syndrome, and I bet a lot of Australians have it and they don’t know it,” Dr Mosley said.
“You can be apparently skinny and still have it. You have these internal organs coated with fat and it’s doing all these sorts of bad things.”
The more Dr Mosley investigated the science, the more he came to believe in the possible benefits of intermittent fasting.
“What researchers say is that we are decedent from a long line of cave men and cave women. So the tradition of feast and fast is built into our genes,” he said.
He said what researchers know is that everybody fasts broadly over night.
“You stop eating at about eight o’clock in the evening and you probably don’t eat again until seven o’clock the next morning.
“What’s happening in your body when that is going down is that your body switches from essentially ‘go-go’ mode, into ‘repair’ mode,” Dr Mosley explained.
Proteins start to be broken down and old cells get cleared out. All the junk goes.
“Now, as soon as you start eating again, that process goes into reverse. So when you go without food for even ten hours, repair starts to take place, you go without food for 24 hours, 36 hours, more repair occurs.”
When we eat a lot we produce more of a growth hormone called IGF1.
It increases activity in our cells, making them divide and create new cells.
Fasting lowers the levels of IGF1, meaning fewer cells are created, and instead the body focuses on repairing existing cells.
The proof could be seen inside a mouse, which was genetically engineered with low levels of IGF1.
At the end of his four-day fast, Dr Mosley’s results were extraordinary.
He decreased his risk of a whole range of age-related diseases.
The big question in his mind was whether he could fast regularly in a more manageable way.
And that’s how Dr Mosley came up with the 5:2 diet.
He knew most people would find lengthy fasts difficult, but science came up with a solution.
Evidence shows that even two days a week of minimal food intake can bring maximum benefits.
“The basics are that you eat normally for five days a week and then for two days a week, you cut your calories down to a quarter of their normal level,” Dr Mosley said.
Full story: The 5:2 diet - Why it works
Gloria Puljak is a teacher and a mother of two who has become a 5:2 convert.
Her battle with weight began after having children.
“I didn’t have a double chin, every time I turned it was a triple chin, my stomach had dimples all over it and no matter how many times I laid flat I still had dimples on it,” she said.
At her heaviest, Glory weighed 82 kilos and her blood sugar levels were dangerously high.
Then she saw Dr Mosley’s documentary, read his book and tried 5:2.
She has lost more than 20 kilograms in a year, and three dress sizes.
She has also turned around her risk of diabetes. Her blood sugar levels are now normal, much to the delighted surprise of her doctor.
“I cannot believe this is my body. I can’t believe I have done this and I have achieved this when it was tricky at the start and then it was so easy,” Glory said.
But losing weight is just the beginning. Fasting may also make us smarter.
In America, groundbreaking research is finding that starving the body fuels brain activity.
It dates back to when we were cavemen. In order to catch food, a starving caveman had to be sharp and agile.
Studies have also found that fasting increases the ability of mice to remember and learn, and decreases their risk of dementia.
And when it comes to exercise, Dr Mosley’s view is that those hour-long gym workouts are 57 minutes wasted.
Instead, intense bursts of exercise – as little as three minutes a week – are the key to longevity.
“We were descended from hunter-gatherers,” Dr Mosley explained.
“When you look at hunter-gatherers and what they do, they have periods of feast and famine, and they have periods where they do quite a lot of walking but they have short bursts where they are either running away from something or running to catch something.
“Our bodies seem to be designed for that.”
Ross Coulthart completed a four-day fast during his investigation into the 5:2 diet, drinking only water and black tea, and eating only miso soup once per day, just like Dr Mosley did.
He weighed just over 104.5 kilograms when he left Australia. He came back weighing 98.8 kilograms.
His blood pressure and glucose levels had returned to normal, when before the fast they had been high, putting him at risk of type 2 diabetes.
“The great thing about it is it puts power back in your own hands,” Dr Mosley said.
“Your health, your future is in your own hands, you can do something about it. I do think that this is one of the simplest and easiest ways you will ever encounter to lose weight. I do genuinely believe that.”
For more information about the 5:2 diet, visit Dr Michael Mosley's The Fast Diet website.
THE FAST DIET by Dr Michael Mosley and Mimi Spencer
THE FAST DIET RECIPE BOOK by Mimi Spencer with Dr Sarah Schenker
FAST EXERCISE by Dr Michael Mosley and Peta Bee
FAST COOK by Mimi Spencer
THE FAST BEACH DIET by Mimi Spencer with a foreward by Dr Michael Mosley