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The Fast 800 by Dr Michael Mosley

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If you're a fan of the 5:2, then you'll welcome the Fast 800 with open arms. While still harnessing the health benefits of the original famed diet, you can now enjoy 300 more calories on your fast days - yippee! This is because, as recent medical research has found, going up to 800 calories makes little difference to weight loss and is low enough to still be an effective way to help you lose weight, improve mood and reduce blood pressure, inflammation and blood sugars. If you're curious about giving it a go, here's what you need to know. 


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What is the Fast 800? 

michael mosley fast 800

Six years ago, Dr Michael Mosley started a health revolution with The 5:2 Fast Diet, telling the world about the incredible power of intermittent fasting.

Now, his recent studies have shown that 800 calories is the magic number when it comes to successful dieting – it’s an amount high enough to be manageable but low enough to speed up weight loss and trigger a range of desirable metabolic changes.

In his new book, he brings together all the latest science – including a new approach: Time Restricted Eating – to create another easy-to-follow programme.


“I lost 16kg in the first 8 weeks and then another 6kg. I’ve never been healthier.” - Denise, 51 

How does it work?

The diet uses the same principles as the 5:2, which involves two days of fasting a week, consecutive or otherwise, and a healthy, mediterranean-style diet for the other five days. 

However, the extra 300 calorie allowance makes it much easier for many to stick to. Dr Mosley said that although many found they could stick to the 500 calories for women and 600 for men, others struggled. So, after recent research, he developed the Fast 800 which he describes it as a simple, one-stop-shop programme, with more manageable 800-calorie fasting days. 

He has tested this new science out for himself; working on his personal rationale that he always tries the things he recommends, he put on 14lb, nearly 10% of his body weight, for the book and then test-drove the Fast 800 with stunning results.  


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What are the health benefits of the Fast 800?

The Fast 800, like the 5:2 diet, boasts a number of health benefits. With the incorporation of a Mediterranean-style diet and two fasting days of only 800 calories, you can expect:

  • A greater loss of fat than on a conventional diet
  • Reduced inflammation (helpful for rheumatoid arthritis)
  • Reduced blood pressure
  • Reduced blood sugars
  • A nutritious, high-fibre diet which can improve bowel function
  • Possible improvements in brain function*

*The results of a 4 year trial doing 5:2 with people who are beginning to suffer memory loss will be available this summer.

Are the results long term?

In our Q&A with Michael Mosley, he said:

"Yes, these diets are sustainable. A recent study followed people doing the 5:2 diet versus a standard weight loss diet in Australia for over a year. Those doing 5:2 lost and kept off more weight - an average of nearly 8kg."

"Dieting is tough and life can get in the way. To stay motivated, I would recommend joining an online course, like the one available at thefast800.com, or a facebook group. You will get lots of tips and support from others."

For more tips, advice and motivation, head to our dieting & exercising forum.


Dr Michael Mosley

Michael Mosley is a science presenter and journalist. After training to be a doctor at the Royal Free Hospital in London, he spent 25 years at the BBC, where he made numerous science documentaries. He is the author of the bestselling The Fast Diet, The 8-Week Blood Sugar Diet and The Clever Guts Diet


Disclaimer: The information on our health pages is only intended as an informal guide and should not be treated as a substitute for medical advice. Gransnet would urge you to consult your GP before you begin any diet if you're concerned about your weight, have existing health conditions and/or are taking medication.

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