Diet Detective interviews author of the popular ‘Fast Diet’

Dr. Michael Mosley is a very interesting person. He trained to be a doctor at the Royal Free Hospital in London, and then joined the BBC (British Broadcasting Corp.), where he is a journalist, TV personality and producer.

He is famous around the world now as the author of the popular The Fast Diet (, which encourages dieters to fast intermittently. “With 5:2 intermittent fasting you eat normally five days a week and diet two days a week, cutting your calorie intake for those two days to [one-quarter] of their normal level,” he explains on his website.

The diet has been trendy, but also controversial.

I had an opportunity to do an email interview with Dr. Mosley while he was filming in France. He is as fascinating as his famous diet.

How did you discover this diet — that is, using intermittent fasting? The story behind why you wrote the book is very interesting. Can you give us the highlights?

About 18 months ago I went to have a routine physical, and my doctor told me that my blood tests had revealed that I was a diabetic with a cholesterol level that was also far too high and would also require medication. This was a nasty shock, particularly as my father had died in his early 70s of complications of diabetes. I am 5 feet 11 inches and about 186 pounds, so I was not hugely overweight. I also eat quite well and am reasonably active.

I have never been on a diet, as I know most of them end in failure, and I also know that standard dieting has only modest effects when it comes to delaying the onset of diabetes. So I went looking for alternative approaches and came across researchers in the U.S. and the U.K. looking at intermittent fasting. The idea is that instead of cutting your calories every day you cut your calories every other day, or perhaps only twice a week.

I decided to make a documentary for the BBC tracking my progress. It would be a reverse Supersize Me, the documentary where Morgan Spurlock put himself on a diet of junk food. I tried different forms of intermittent fasting before settling on a version that I felt I could stick to. This consists of cutting your calories by one-fourth for two days a week. On a Monday and a Thursday I would eat just 600 calories a day. For the other five days a week I would eat normally. I called this the 5:2 Fast Diet.

On this diet I lost 19 pounds of fat over three months, and all my blood levels returned to the normal range.

The diet seems so simple. Is it really just eating normally five days a week and restricting calories (500 for women; 600 for men) the other two days?

Yes, it is that simple. Actually doing it can be quite tough, particularly at the start. The foods you eat on your fasting days are also important as they should keep you full but also ensure maximum nutrition. I recommend protein (eggs, meat, fish) and lots of vegetables.

Can you really eat whatever you want on the five unrestricted days?

No, you can’t. If you overeat on the other five days you will not lose weight or get benefits. Cutting your calories to one-fourth two days a week means you will cut your calorie intake by about 3,000 calories a week, which translates into around 1 pound of fat lost.

What’s the theory behind the Fast Diet? What does it do for you physiologically and psychologically?

Many people find it easier than standard dieting because instead of being on a diet seven days a week you are only dieting for two days. People say they can exercise their willpower and resist pizza today if they know they can have it tomorrow.

On a physical level this pattern of eating seems to better mimic the way our remote ancestors would have eaten, i.e., feast and famine. Our bodies only get on with essential spring cleaning, getting rid of old and broken down cells, when we don’t have food in our system. That’s why eating lots of small meals a day is not a good idea.

What are some of the tricks or tactics you use to make sure the Fast Diet works?

The main one is to approach it with a positive mental attitude rather than with fear and trepidation. Much of what you may have been told about short bursts of fasting is simply not true. Your blood sugars will not fall after a couple of hours without food; in fact, after a meal there is a drop, and then blood sugars stay constant for about 60 hours even if you don’t eat at all.

Similarly, “starvation mode,” the idea that your body will try to hold onto fat, does occur, but only after many days or weeks without food. The initial reaction of your body to a reduction in food is to speed up your metabolism.

The recipes in The Fast Diet and The Fast Diet Recipe Book are balanced to ensure they give you maximum nutrition for minimum calories

Do it with a friend or family member and you will also find it easier.

What kinds of results should a person expect?

You can expect to lose, on average, 1 to 2 pounds a week. Most of that will be fat. In fact, the studies have shown that on a 5:2 diet you will lose almost twice as much fat per week as on a standard diet.

Is there any validity to your critics’ claims that the diet is unhealthy and that it may be bad for the metabolism?

There have been more than a dozen studies of intermittent fasting, following hundreds of men and women for periods of up to a year. These studies all suggest that intermittent fasting is safe and leads to greater improvements in key biomarkers such as insulin sensitivity than standard diets. Some critics seem to be unaware of the research and continue to espouse long-defunct theories, such as “starvation mode.”

You also researched exercise programs; what did you find out?

I found out that you can get many of the benefits of exercise from doing just a few minutes of intense exercise a day. It is called HIT — high intensity training.

Do you have a favorite healthy recipe?

I love breakfast, and one of my favorite recipes is a mushroom and spinach frittata: eggs, mushrooms, spinach, and all for just 270 calories.

What’s your favorite healthy ingredient? What’s the one thing you’d suggest people keep in their kitchen if they want to cook healthy meals?

My favorite healthy ingredient is garlic. It adds lots of delicious flavor, and the compounds in garlic are said to reduce fatty deposits. Plus, it keeps vampires at bay.