How the fasting diet became a publishing sensation

A new diet craze has swept the UK. The book of the diet has sold 350,000 copies in the UK and 100,00 in the US. It swept to the top of UK's Amazon's best seller list and has only been displaced by a spin-off publication, the Fast Diet Recipe Book. The diet involves eating what you like for five days and fasting for the remaining two. It promises to help you lose weight and live longer.

The co-authors of the book are TV presenter Michael Mosley and diet journalist Mimi Spencer. Mimi was a well-known diet sceptic but her conversion began when she saw Michael Mosley present an edition of BBC television's science programme Horizon in summer 2012[2].  Mosley tested the diet with astonishing results in an episode called "Eat, Fast Live Longer[1] .  Mimi Spencer was dispatched by a weekly newspaper to investigate and was sufficiently convinced to suggest that they should collaborate on a book.


What does the 5 to 2 fasting diet involve?

The basic idea of the diet is that you fast for two non consecutive days of the week and eat normally the rest of the week. Studies in the US[3] [4][7]have shown that our bodies react to periodic fasting by changing their metabolism and that this can help you to lose weight as well as cutting the risk of cancer, heart disease, diabetes and even Alzheimer's.

You don't go totally without food on the two fasting days but you do drastically reduce your calorie intake; women to 500 calories per day and men to 600 calories per day. The diet encourages adherents to get most of these calories from protein, leafy veg and a bit of fat. According to the studies it's better to eat what you like on the five non fast days and people who do are more likely to lose weight than people who continue to restrict themselves.

The argument is that human beings evolved to cope with periods of feast and famine and that drastically restricting calories periodically on a regular basis can have beneficial effects. It has been demonstrated that drastically reducing calories can prolong life in rats and studies where subjects fasted on alternate days have  shown that fasting in this way can have a similar effect on humans. The US studies suggest that intermittant fasting controls cholesterol, blood glucose and the growth hormone implicated in cancer and can boost protective brain chemicals too[6]. The BBC2 programme suggested restricting calories on just two days a week can have a similar effect.


The book by Michael Mosley and Mimi Spencer that has swept the UK and could now sweep America.
Healthy Eating
Credit: Morguefile

What do people like about the 5 to 2 fasting diet

The thing that people like about the 5 to 2 fasting diet is that it can be woven around your social life and you do not feel like you are depriving yourself. You can go out with friends without feeling like a kill-joy and the fact that you can eat normally most of the time means that the two days when calories need to be restricted are easier to put up with.

It's said to be particularly popular with men who can not be bothered with conventional diets and fussing over much about what they eat.

What's less good about the 5: 2 Diet?

According to Dr. Susan Jebb of the Human Nutrition and Research Unit, Cambridge, quoted in Good Housekeeping Magazine[5], "There are no long-term studies on people and no agreement on how often you should fast and conditions in the lab are different to real life. You won't lose weight if you overeat on non fasting days and there's some concern it could lead to a cycle of bingeing and starving.

Dr. Jebb's Good Housekeeping assessment concludes that, "If regular fasting turns out to benefit our metabolism and burn fat round the middle, as animal studies suggest, it could be revolutionary. Until then,"Its best to think of it as a weight loss strategy, says Jebb, "People often find it easier than dieting every day, so if you need to lose weight, you're not pregnant and your essentially healthy, give it a go."

Fast Diet interview with Dr. Michael Mosley

The recipe book that accompanies the diet.