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.
Calyn's story: My brother, my hero
Kids cage fighting on the rise
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.