The new fad: The Fast Diet

Brace yourselves! A new diet is getting lots of media attention and hype.  This new fad is called the Fast Diet, that comes from a book written by Dr Michael Mosley and Mimi Spencer. Dr Mosley is a medical journalist and Mimi Spencer is a food and fashion writer.  The Fast Diet is also known as the 5:2 diet. It involves five days of normal eating, and two days of fasting (approximately 500 calories for women and 600 calories for men). According to the authors, the two (non-consecutive) days of fasting per week will result in the metabolism working harder on the days you don’t fast. To give you a bit of an idea about how far those 500 calories could stretch: one medium banana has about 100 calories. One orange also has about 100. There are about 250 calories alone in a cup of plain cooked pasta. Add a bit of sauce and cheese and you’ve probably reached your limit for the day.  Normal daily intake for a woman is 2000 calories. So you’re basically cutting your recommended food intake by 75 per cent. Feeling hungry yet?

The Fast Diet is intended to result in weight loss and general better health all round.  The 5:2 diet writers claim that other than helping people lose weight, 5:2 diet can bring other significant health benefits, including:

  • increased life-span
  • improved cognitive function and protection against conditions such as dementia and Alzheimer’s disease
  • protection from disease
  • It’s worth noting that there are certain groups for whom the diet is not advised. Those who are pregnant, or suffering from an eating disorder, or Type 1 diabetics should not fast. It’s also recommended that children and those who are already extremely lean never fast.

So what do we think?  There does not appear to be any research evidence that looks directly at the 5:2 diet.   Some research has been tested out on mice and monkeys and other on extremely obese women.  The sample sizes have been small, and testing on animals particularly rodents is not useful in such research (given their life-span).
Due to the very real uncertainties about the Fast Diet, especially as little is known about whether it could be harmful to health in the long-term, we recommend you stick to the tried and trusted methods for weight loss and disease prevention:

  • eating a healthy balanced diet with at least five portions of fruit and vegetable a day
  • taking regular exercise
  • quitting smoking if you smoke
  • drinking alcohol in moderation
  • seeing a dietitian to discuss a suitable an safe plan for your weight loss

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