The 5:2 inventor on ‘mini fasts’ and his new secret to rapid weight loss

By | June 6, 2019

This article first appeared in The Telegraph

Dr Michael Mosley is in the business of making people healthier, not upsetting them. Whether he is talking about people struggling with eating habits, or the food industry pushing unhealthy snacks, he always chooses his words carefully. But the man who revolutionised eating with the 5:2 diet is frustrated by the speed at which things change.

NHS nutritional advice tells us first about the importance of eating your five-a-day, and then it says that your meals should be mainly based on starchy foods like potatoes, bread, rice and pasta. So the NHS is telling us to keep up bodies constantly charged with carbohydrates, as if we have learnt nothing about the benefits of the intermittent fasting that was popularised by Dr Mosley.

“The NHS needs to move on, but because it’s based on consensus these things take a long time to change and that is frustrating,” he told my Healthy Beast podcast. “Having your blood sugar constantly elevated is not a good thing. Your body is constantly having to produce insulin, and this ultimately causes insulin resistance. This causes your cells to rebel and you need to pump out more and more insulin and that takes you down the road to various cancers and particularly type-2 diabetes.”

Dr Michael Mosley










Dr Mosley speaks from personal, as well professional experience. In his mid-50s he was diagnosed as having type-2 diabetes. He had trained as a doctor and was then working as a science writer, so rather than going on medication, he decided to research non-medical solutions.

He had a telling conversation with a surgeon who performed bariatric surgery to reduce the size of obese patients’ intestines, who said: “I don’t see myself as a weight loss surgeon, I am someone who cures type-2 diabetes.” This led Dr Mosley to make the 2012 Horizon documentary Eat, Fast and Live Longer where he went to America and spoke to the leading experts on fasting.

By radically reducing his own calorie intake he lost weight and was able to reverse his diabetes. Now aged 62, his blood glucose levels remain normal. Using himself as a human guinea pig he ended up developing the 5:2 diet, where people would eat normally five days of the week, and have restricted calorie intake on the other two days of the week.

He is now back with The Fast 800, a book and online course that takes into account the latest scientific research on fasting and presents a number of diet options, including a modified version of the 5:2. The title refers to one of the options, which is to eat 800 calories a day for a minimum of two weeks, up to a maximum of 12 weeks.

That sounds a like a ‘crash diet’ to me – one of those negative terms that we’ve been warned against. But there is nothing wrong with losing weight quickly, according to Dr Mosley, because it mimics natural conditions that our ancestors had to endure.

“It’s a good idea to have longer periods without food. Our ancestors had periods of feast and famine. Our bodies are designed to do that and it’s quite clear that during the periods that you are not putting food into your bodies, a lot of repair goes on.”

So we’re wrong to think that rapid weight loss is bad for your health? “If you do it properly then the evidence seems to be that it does lead to long-term benefit,” says Dr Mosley. “There are lots of bad diets out there, and some of the old rapid weight loss diets were very bad. They were very low calorie, 3 or 400 calories a day, they didn’t have adequate levels of protein and the nutrient levels were poor; a lot were based on supplements or sachets that contained absolute junk. Not surprisingly the people on those diets tended to do rather badly.”

He added: “You need good quality protein, at least 50g of good quality protein every day, that’s one of the most essential nutrients. But beyond that there have been three really decent long-term trials that I’m aware of using the 800-calorie approach, which is pretty rapid weight loss, 800 calories a day for up to 12 weeks. Two [of those studies] have now got data gathered over two years and those doing the rapid weight loss did a lot better than people doing the slow and steady stuff.”

Dr Mosley also speaks persuasively about breakfast. He recommends daily “mini fasts” where you restrict eating to an eight to 12-hour window. So if you eat anything in the evening, this means no breakfast. This is particularly important, he says, because the process of autophagy, where the body starts to break down old cells and repair itself, “only starts to kick off seven to eight hours after you’ve stopped eating anything”.

But what about this idea of breakfast being the most important meal of the day? More lies and nonsense we’ve been sold?

“Your gut needs periods of downtime when it’s not dealing with food when the body gets on with the clean-up processes. Breakfast is a Victorian and post-Victorian thing. Prior to that having breakfast was seen as a form of weakness. People wouldn’t expect to eat until midday. Historically it’s an anomaly and the idea of having three meals a day is largely a modern construction and there seems no reason to keep it.”

If this sounds preachy, what is winning about Dr Mosley is that he completely understands the temptation everyone faces.

“I do acknowledge my weaknesses and also I do wrestle with my demons,” he said, adding: “If there is junky food in the house I will eat it, despite everything I know.”

So knowledge does not make it easy. But that doesn’t mean you should give in. “Snacking is one of the things that has driven obesity. It was encouraged by the snack food industry and oddly enough also encouraged by dieticians,” he says. And as for the NHS advice, he adds, it is “suitable for a peasant economy where people are doing a lot of physical activity. In the modern world that simply isn’t true.”

Dr Mosley doesn’t like upsetting people, but if he will permit me to put it more starkly, his advice goes something like this:

  • Stop stuffing your face with carbs all day
  • Give your body some time off from eating so it can recover
  • Big parts of the food industry cares more about your money than your health
  • Low blood sugar is good, not a sign that you desperately need to eat
  • Being a healthy weight is not about looking good, it is about not getting sick and dying

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