The Fast 800 Keto

by Michael Mosley

A keto diet - where you flip your metabolic switch, going from burning sugar to burning fat for fuel - leads to significant weight loss and other potential health benefits. But one of the challenges of a standard low-carb, high-fat keto diet is that it can be hard to stick to.

Dr Michael Mosley's Fast 800 Keto is both more effective than a conventional keto regime, and healthier and more sustainable. The secret to this new approach is that it combines keto with intermittent fasting, which means you go into ketosis faster, while also being able to enjoy delicious Mediterranean-style food.

Based on the latest dietary science, this book presents a simple, highly flexible three-step programme to ensure you lose weight rapidly and safely, while preserving your metabolic rate. It includes protein-rich, low-carb recipes and easy-to- follow menus from bestselling author Dr Clare Bailey, and all the other tools you need to shift stubborn fat and transform your health for good.

Genres: Health, Nonfiction, Food, Science, Diets, Reference, Self Help

Paperback

Published December 29, 2021

About the author

Michael Mosley was a British television journalist, producer, and presenter who worked for the BBC (amongst other broadcasters) from 1985 until his death in 2024. He was probably best known as a presenter of television documentaries on biology and medicine, and his regular appearances on The One Show.

Born in Kolkata, India, the son of a bank director, Mosley studied philosophy, politics and economics at New College, Oxford, before working for two years as a banker in the City of London. He then decided to move into medicine, intending to become a psychiatrist, studying at the Royal Free Hospital Medical School (now part of UCL Medical School).

Becoming disillusioned by psychiatry, upon graduation Mosley joined a trainee assistant producer scheme at the BBC in 1985. Since then he produced and presented many documentaries on science and/or medicine. He was an advocate of intermittent fasting and low-carbohydrate diets who wrote books promoting the ketogenic diet.

Mosley died on the Greek island of Symi on 5 June 2024.

Reviews

[Catherine · Rating 5 out of 5]

Excellent update to the latest research. Just wish this had been available thirty years ago!

[Rhonda · Rating 5 out of 5]

Michael is so easy to relate to. I appreciate learning from all the research he has done, and naturally it's reassuring that he and his wife are both doctors and giving advice from that perspective. As for the diet itself, I am seeing it working in my husband and myself, and am loving the meals. The initial reaction to the size of the meals is that there's no way you are going to be satisified when you're finished, but you mostly are. And the meals are delicious. Like, delicious.

[Lee-Ann · Rating 4 out of 5]

Up to date research. I read The Fast 800 in December 2020 and changed my life in 2021 by loosing 15kg. I feel much healthier, have more energy and sleep better. You can easily live on 800 to 1000 calories a day. Plan your meals, download a calorie counting app and walk.

[Wendy · Rating 1 out of 5]

Having read the book I am unlikely to refer to it ever again

This book feels hurriedly put together, presumably to ensure it didn't miss the wave of interest in keto combined with fasting. It is a skeleton structure of Mosley's diet book formula that they either didn't have the time or perhaps the inclination to dress. Whilst the relevant boxes are ticked in terms of references to research and inspiring individual stories it all seems very patchwork and borrowed - indeed it is pointed out a few times that previous books already provide more detail. Don't bother with the recipes - there are far better keto cook books available. I learned nothing new from this book despite the fact that I am really keen on this approach with some good results to date.

[Mr Rob Saunders · Rating 5 out of 5]

Great book to start a Keto way of eating.
Having been on this eating plan for nearly 3 years it’s a great breath of fresh air to have a British slant on the diet.
It has given me a much needed kick up the backside to maintain my healthy eating.

BTW- have lost between 6 and 7 stone give or take. 12 inches off my waist. It’s given me a new lease of life. Really works well with the intermittent fasting.

[John · Rating 3 out of 5]

DR. Mosley is trying to cash in on the popularity of the Keto diet me thinks. The book appears to be hurriedly put together and although the content is ok the modus operandi here is to steer you towards the Mediterranean diet because this is supposedly better for you long term. Now, I wonder who has a book and business centred around that?

[Rhiann · Rating 4 out of 5]

Much the same as the original Fast 800 with a bit more focus on protein & carb intake. Good for a refresh and motivation.

[Gijs Limonard · Rating 3 out of 5]

Filed assuredly under the rubric ‘midlife literature’; the ideas are ok (calorie restriction, low carb, high protein diet; excercise) but the scientific underpinnings are weak; in particular the 800 kcal per day is not advisable in the long term.

[Maria · Rating 4 out of 5]

Well I’m 18 days in and already feeling the effects on my waistband! Good, clear, helpful book to get you started. Backed by MM’s own research and experience on the diet, this is a non preachy approach and has a clear plan to maintaining once you’re at goal weight.

[Elien · Rating 4 out of 5]

Reading the updated version of the fast 800.
Planning to try the 'lose a stone in 21 days.'
Knowing how much water and glycogen stores you lose on the first week, that is entirely possible.
My brother might tag along this time, so there's extra pressure to cook the meals properly and portion them right.
The fajita bowl from the keto recipe book and the parmazan chicken are going to be one of our first meals.
My biggest struggle is going to be able to sleep and not get keto rash.
I know I can get extreme and fast results with this which is exactly what I have been craving after fast weight gain.

[Tracy Mackay · Rating 4 out of 5]

Thank you to QBD Books for my copy.
This was an interesting read learning all about fasting, keto and the importance of protein. It was a quick read and some of the recipes sound delicious. There are some photos which look fantastic but it would have been nice to have a photo for more of the recipes. I have already started eating more protein and it definitely makes a difference as I feel fuller for longer and are not craving as many snacks as before.

[Tracey · Rating 4 out of 5]

This is the updated ‘Fast 800’ book, with updated research and a number of tweaks to the plan, one of which is obviously keto. My husband and I have just started this diet and we’ve already lost several kilos in only a few days. [Update: In two weeks, hubby has lost almost 10 kilos and I've lost almost 6 so it certainly works and neither of us are hungry.]

[Sue Johnson · Rating 4 out of 5]

Here we go again. Not very different from the first book. Might actually try to use the recipes this time.

[Terri · Rating 5 out of 5]

Might give this a go. Once ive emptied the sweet cupboard obvs

[Ella J. Smyth · Rating 5 out of 5]

What an amazing book. I've been dabbling with the keto diet for years, and never managed to stick to it. It just seemed so much kerfuffle and bother, especially when traveling or on vacation. I also never lost much weight with it, mainly because the purist keto philosophy is all about medium protein, very low carb, and to make up the calories, lots and lots of fat.

I shudder at some of the recipes I tried like broiling salmon in a cup of double cream etc. Sure, it tasted great, but there was a major issue: yes, not all calories are created equal in terms of insulin response. But eating 3000 calories per day, which I regularly did, won't lead to weight loss, even though my glucose levels were super steady.

Cue Dr. Mosley and Dr. Jason Fung. I tried the 5:2 diet way back when, but couldn't do the 600 calories twice a week. But when you combine keto with 800 calories a day for a LIMITED AMOUNT OF TIME (Michael suggests no longer than 12 weeks)? Wow, that works for me so well! I've been eating the most gorgeous meals and lost 5.5lbs in 4 days. Without cravings or having to willpower through. I'm just not hungry. At all. Not even in the mornings.

I do Time Restricted Eating (TRE) which is basically intermittent fasting. 18 hours? No problem. Again, I've never been able to do that before without suffering hunger pangs.

I'd also highly recommend the blue recipe book that complements the diet. The meals are easy and extremely satisfying. The first day, I had a chickpea / lentil soup with harissa, basically thrown together from cupboard staples. Not your usual keto food! But the food was so tasty and kept me full until the next afternoon at 19g carbs. Michael recommends under 50g of carbs for his plan, so that was well within tolerances.

[Monica Willyard Moen · Rating 3 out of 5]

I have some ambivalent thoughts and feelings about this book. There are some very nice recipes, and much of the information seems medically sound. However, most of the doctors I have seen in my lifetime have told me that 800 calories is not a safe level for a person to eat for several weeks at a time. My current primary care and endocrinologist team of doctors is very supportive of keto, low carb eating, and using supplements and vitamins to address health issues were possible. However, they are not comfortable with their patients going below 1400 calories a day except for doing intermittent fasting a couple of days a week. The section of the book talking about reduced calorie days and the principles of fasting seems very solid. I will try many of the recipes. I don’t think I’m comfortable following the eating plan as stated without close medical supervision though. The author lights to contrast his 800 calorie plan with unrestricted keto eating, and that looks like an all or nothing logical fallacy to me. There is a middle road that is not unrestricted eating that seems more sustainable and healthy. This looks a lot like some of the crash diets I used to see back in the 1970s and 1980s.

I will refer to the book for its recipes which do look like they are very flavorful. However, I couldn’t recommend this book to anyone who wanted to try the keto way of eating to lose weight because I just don’t have confidence in all of its recommendations. I wish that were not the case.

[Jo-Ann Duff · Rating 3 out of 5]

I’m never one for fad diets or ones that restrict food groups. It’s just not me. That’s probably why I’m a little curvier and softer in the middle than I should be. However, I do try and exercise when I can and I’m always looking to eat a little healthier and of course, lose a little weight.

The Fast 800 Keto was a quick read for me. I personally didn’t buy into it all and didn’t suddenly find a groundbreaking way to live and lose weight in a heartbeat. What I did find though, were little reminders of what I know I should be doing. Low carb, non-processed, high protein with a little intermittent fasting thrown in.

I did have a huge problem with recipes printed in the back of a paperback book. Recipes should always be on white glossy paper with pretty images to entice you to cook and create. I glanced at a few, but it’s just not the inspiring medium for recipes and you will not change my mind.

Maybe I would have enjoyed and got a little more out of The Fast 800 Keto if the book itself was printed differently. Either way, I did end up ordering healthy non-processed groceries for the month, and I will be adopting some elements of the keto diet. I just won’t be drinking the Kool-Aid.

[Cidney · Rating 3 out of 5]

I have some of his other books and this is a bit of an add on to the last one.

The first half of the book is taken up by the science around keto diets, then a bit of motivation, and then what everyone is waiting for, the recipes!

Like Michael I'm diabetic and need to lose weight, have been plodding on slimming down so for the past couple of years and for the most part my weight is remaining steady, but still need to lose some more. I believe in Michael Mosley, primarily because he is a doctor and also because he delves deeply into the science behind every book/radio-tv programme he does, but what I have an issue with is the diet itself.

I know that portion sizes matter but there doesn't seem to be a lot of substance in the meals themselves, if you are not (even particularly) a big meat eater then you seem to miss out a bit on diets, unless you are vegan/vegetarian where numerous cookbooks exist. So if you don't want to go vegan or vegetarian then books to lose weight are a bit hit and miss for you it seems.

I also have to admit that although I like Michael Mosley, his books are getting a bit same-y!

[Andie Red · Rating 1 out of 5]

not worth it

This book is a great disappointment, i am so glad bought it in the sale for .99p because it is not worth even that.
First it has no pictures, please! Are you so foccus on making money that can not afford to add pics?
Second. The recipes, boring and sll are a little tweaking from the recipes in the oder books.
And last all the blah blah, well same stories we have read in the other books.
So, I can help you saving some time and money by buying this book. Keep the same principles of the other books being sure to lower your carbs and to do this make some changes in the old recipes, take away the little “whit wolf” we had, aka pasta, bread, a potato. Keep to the 800 calories a day and when you are done o fed up, introduce little carbs slowly and expect a gain.

[Rory · Rating 4 out of 5]

This is an interesting book and Michael has had great success himself and with the people that have trialled this way of eating.

He is rather too optimistic, claiming that everyone will lose lots of weight on this eating plan (I didn't).

He is clearly anti vegan (which I know from his other books and podcasts) and does not include a meal plan for them. There are meal plans for pescatarians and vegetarians but not vegans (even in this day and age) and just a note to say that vegans will have to plan their protein choices carefully. I feel that we, vegans, want the same plans and help as everyone else.

But the plan looks good and a lot of people have had great success with it.

[Louise · Rating 5 out of 5]

I wanted to lose weight for my health but didn’t know which diet plan to follow. Having seen the successes online of others who have done Michael’s other diets 5:2 and Fast 800 and having read how beneficial to health Keto can be, I decided to order this book and the Keto recipe book.

I am pleased I did. The advice in the book is easy to digest and understand and the recipes don’t feel like diet food. Very impressed with everything so far, even though I am just starting out on this journey.

As I’m typing this (17th May 2025) so far so good!
Let’s hope the numbers on the scales continue to decrease.

[Alejandro · Rating 4 out of 5]

I like Michael Mosley's books, his ideas are super simple and easy to implement. The Fast 800 Keto is 90% the same as the original Fast 800, so it isn't worth reading if you read the original. These were my impressions:

- The book aims at making your overall lifestyle healthier, not just to lose weight. I was looking for healthier habits and you get some good ones.
- The idea of eating 800 calories a day for weeks seems extreme, but it isn't so hard in practice. First few days are tough but I quickly got used to it
- You might be surprised how many "meals" you can make out of 800 calories if you manage it well
- The results come very fast, I felt lighter, leaner and better with myself after only 2 days (the longest I have done this is 2 weeks)
- There are many recipes in the book based on the Mediterranean diet. However, you don't really need to use recipes, just stick to the 800 calories and make sure you don't eat processed food and that what you do eat is balanced in macros. The results will come. That's the biggest advantage of the approach, the simplicity.
- For me personally, the best way to implement it was to simply have 1 snack at lunch time and a "large" dinner because it is at evenings that I get cravings. You manage this as you wish, you can spend your 800 calories in 8 or 10 small snacks throughout the day if that works for you.

Although I'm not into diet books and haven't read many I can compare to, this book was really useful and I plan on implementing some of the ideas in it on permanent basis.

[Brad · Rating 3 out of 5]

As with all Michael Mosley books it is interesting reading but not bogged down with scientific jargon. Was slightly disappointed that he was dropping hints on buying stuff off his website all through the book.

[Maryan Dawson]

It's a great diet. After reading the book I signed up to the diet online and have lost 13 kilos in three months. The book is very easy to read and I found its basis in science and research compelling and reassuring. I bought the book ages ago but have read most of it in the last three months.

[Jenny Hall · Rating 4 out of 5]

Hope it works 😂

[Felicity Waterford · Rating 4 out of 5]

Some fascinating information that’s put me on a healthier path.

[Kabir · Rating 4 out of 5]

Good read. All the latest research. Plenty of validated sources cited. Easy to understand and apply in real life. A few too many case studies and examples.

[Mel · Rating 4 out of 5]

Good to have the most up to date research but very similar material to the other Fast 800 books and way too much plugging of his Fast 800 shakes.

[Pam Saunders · Rating 2 out of 5]

Keto works, this book does not.

[Brian Trinder · Rating 5 out of 5]

A "must read" for all of us! Easy to understand and lots of handy tips on how to improve your overall health and well being.