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Will the REAL fast diet please stand up?

The scientist responsible for most of the human research on fasting for weight loss says her studies have been misrepresented in fasting diet books. Now she’s launched her own

The fasting revolution happened overnight.  One moment we were all Atkins-ing, or Paleo-ing or at least low-carbing and the next we were drinking miso soup all day every Monday and Thursday and apologising for our narkiness with the words ‘Sorry, it’s a fast day and I’m hangry.’

krista_facebookNow every month seems to bring with it a new fasting diet book. But the scientist responsible for most of the human research on fasting for weight loss, Dr Krista Varady (left), now claims that such books have misrepresented her research.

If you believe the hype, fasting diets will help you lose weight where other diets fail and have good scientific studies showing not only the weight loss but the health benefits of fasting such as longer life and reduced cholesterol.

But while most of the fasting diet books encourage a 5:2 approach (that’s five days eating what you like and two days fasting) Dr Varady’s research – quoted extensively to back up fasting diets – relates to alternate day fasting; that’s one day fasting, one day ‘feeding’ or eating what you like.  According to Varady, there’s a crucial difference.

It kicked off with a Horizon documentary two years ago in which Dr Michael Mosley, a medic and journalist interviewed Dr Varady, an obesity researcher who has been studying alternate day fasting (ADF) in humans for the last ten years.

Varady has published some 25 papers in peer-reviewed journals about fasting and its effects on both animals and humans looking at everything from how much weight was lost to effects on blood pressure, diabetes risk and cholesterol.


In her experiments Varady’s subjects did alternate day fasting in which they ate a 500 calorie meal for lunch on one day – the fast day – and then the next day ate what they liked and continued on this one day fasting, one day feeding pattern.

When Michael Mosley tried ADF on himself, he found it too rigid so decided to try fasting two days a week (Mondays and Thursdays) and eating normally for the other five.  It worked for him and he lost 20 pounds.

Then, when writer Mimi Spencer interviewed Mosley about it for the Times, she tried Mosley’s method herself and also lost some 20 pounds.

The obvious next step was a book and so Mosley and Spencer’s The Fast Diet was born.

It’s based in on what is now known as the ‘5:2 diet’ and was released earlier this year.  It’s sold a staggering 350,000 copies in Ireland and the UK, 100,000 in the US and garnered a growing number of rapidly-shrinking devotees on both sides of the Atlantic.

The 5:2 premise advocates cutting calories to 500 for women and 600 for men for two non-consecutive days a week and eating normally for the rest of the week. A stream of other 5:2 diet books have subsequently been launched (see above).

But now, Dr Krista Varady, an assistant professor of nutrition at the University of Illinois-Chicago, whose research it is that was quoted in the original The Fast Diet and its subsequent hybrids, is not pleased with the way her research has been used.

‘My research on alternate-day fasting has been misrepresented in the book,’ Dr Varady told Healthista in September last year.

‘Mosley used my research, which looks at fasting three to four days a week, to support his diet, which encourages fasting two days a week.’

Mosley says he was partly inspired to try the 5:2 approach after reading research done by Michelle Harvie, a dietitian who wrote The 2-Day DietHarvie has published two papers that followed women on a two day fasting diet for six and four months respectively. Read one of them here

‘I respect Dr Varady enormously as a scientist,’ Dr Micheal Mosley told Healthista.  ‘In April we made changes she requested to the book so I am surprised she still feels upset about the way we represented her research. I never claimed the 5:2 approach was the same as alternate day fasting and in The Fast Diet set out to show the evidence for different types of fasting diets.’

‘The Fast Diet is about his [Mosley’s] experience,’ says Varady.  ‘But unfortunately he actually used all of my research on alternate day fasting to support all of his points. Scientifically you can’t take studies that look at three or four days fasting a week like mine and say it’s the same thing and that you’re going to get the same health benefits when you just fast two days a week.’

Varady asked Mosley’s publishers to remove all references to her research from future reprints of The Fast Diet and Short Books confirmed they did this in April last year.

‘I’ve been doing this research for ten years now on both animals and humans and I didn’t think it medically responsible to write a book until I had run at least 4-500 people through these studies,’ says Dr Varady. ‘So I waited until I had enough research.

‘To be honest, it was upsetting that Mosley and Spencer jumped in and not only wrote a book with no scientific evidence but then took all of mine and tried to apply it to something that had never been adequately researched before, this 5:2 diet’.

Fasting Slider

The reason Alternate Day Fasting (ADF) works in her research she says is that when subjects fast every other day, they experience  a hunger-reducing effect on the feed day.

‘We don’t know the mechanism exactly, whether it’s the stomach shrinking or something else, but what we find is that if you’re fasting one day and then the next day you get to eat whatever you want, for some reason people don’t binge on that feed day.  They end up eating only about 110 per cent of their needs and that leads them to lose weight,’ says Varady.

How much weight exactly? ‘In general, people lose about 10-30 pounds in about eight weeks and after about six months, people lose on average about 25 pounds,’ says Varady.  ‘The weight loss is at first dramatic and then peters off.  The most anyone has lost in our studies is 55 pound after six months.’  Varady now has a Facebook page where success stories are post their tales and one man lost 130 pounds.

So, what do Varady’s studies show happens after subjects have lost their weight on ADF? It doesn’t exactly sound like a way of life.  ‘Obese subjects that lost the weight with ADF are actually able to keep it off by doing a modified ADF where they consume 1000 calories over two meals instead of 500 over one,’ she says.

Lastly, what if you’re not obese and only have about ten pounds to lose?  ‘We ran a study on normal weight individuals who only needed to lose 10-15 pounds and we found it worked for them too,’ she says.  ‘On average, people lost ten pounds in 12 weeks.’

How to do Alternate Day Fasting – Healthista asked Dr Varady what in her research has been shown to work and what doesn’t if you’re doing ADF


  • Alternate a fasting day with a feed day  Each fasting day eat one 4-500 calorie meal (women) or one 5-600 calorie meal (men) ideally at lunchtime.  Each feeding day, eat whatever you like.
  • Exercise moderately in the morning  ‘About 40 minutes after exercise people get a surge in hunger so it’s best they exercise and then are able to have a meal.’
  • Have hot beverages with no sugar in them between meals on fast days  ‘Drinking a warm beverage, especially at night tricks the body into thinking you have had a small, warm meal and lowers hunger,’ says Varady.
  • Eat enough protein on fast days  ‘Proteins are associated with fullness and satiety so having enough meat or chicken or a good serve of beans if you’re vegetarian on your fast days is essential to keep you from getting too hungry.’


  • Exercise in the evening on fast days or you may want to eat more
  • Break up your meals on fast days  ‘For some reason, having three 150 calorie meals throughout the day doesn’t work as well for people as having one 500 calorie meal in the middle of the day on fast days,’ she says.

The Every Other Day Diet by Dr Krista Varady and Bill Gottlieb is published by Hodder & Stoughton and out January 9th, 2014

Go to the Every Other Day Diet Facebook page



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