The Fast Diet by Dr Michael Mosley: Book Review
If you have heard of the 5:2 diet, this is the book that made it famous. Dr Michael Mosley, working with journalist Mimi Spencer, turned a BBC documentary into the title that made intermittent fasting a household idea rather than a fringe one.
Authors: Dr Michael Mosley and Mimi Spencer · Publisher: Short Books, 2013 · Length: about 224 pages (later editions run longer)
What The Fast Diet covers
The method is right there in the name. You eat normally five days a week and cut back to roughly 500 calories (for women) or 600 (for men) on two non-consecutive days. It grew out of Mosley’s documentary Eat, Fast and Live Longer, and it pairs an accessible tour of the science of calorie restriction with the practical side: calorie-counted menus, meal plans, and recipes from Spencer.
The division of labour works well. Mosley handles the medical and research framing in plain language, and Spencer makes the two fasting days livable with real food rather than theory. A later revised edition adds newer research and reader feedback.
Who it’s best for
Beginners who want a simple, flexible structure they can fit around ordinary eating, and who prefer counting two easy days a week to watching a daily clock.
Key takeaways from The Fast Diet
- 5:2 restricts calories on two days and leaves the other five normal.
- Fasting days are about 500 calories for women, spread across the day if you prefer.
- The approach is deliberately flexible, so the two days can move around your week.
- Most of the difficulty is mental, and the book spends real effort making the fasting days easier.
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Fasting that adapts to your cycle
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How it fits cycle-aware fasting
The Fast Diet treats every week the same, which is where women often come unstuck. Two very low-calorie days landed in the week before your period can hit sleep, mood, and cravings hard. If you like the 5:2 structure, many women find the two low-calorie days easier in the first half of the cycle, with more room to ease off in the luteal phase. Our guide to the best fasting schedule for women shows how, and if you are weighing whether this style of fasting suits you at all, is intermittent fasting bad for you covers the limits honestly.
Where it falls short
The Fast Diet popularised 5:2 ahead of robust long-term human trials, so some of its longevity and health claims rested on early or animal data. It holds up as a weight-loss structure, but treat its claims about aging with care. For the rigorous, up-to-date evidence those early claims lacked, see our review of The Fasting Fix.
The verdict
A genuine classic and still one of the easiest ways into fasting. If you want to see how 5:2 stacks up against the other methods first, our review of Intermittent Fasting For Dummies is the neutral map. Just remember it was written for a general audience, so the cycle-aware adjustments are yours to add.
This review is part of our roundup of the best intermittent fasting books.
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