Sunday, 2 June 2013

The 5:2 Diet and Variations on Alternate Day Fasting

Last Post I introduce the Hunger Games Challenge: Jo is testing out the 8 Hour Diet, while I'm testing out the 5:2 Diet.

So, before getting into the actual challenge, I had better explain what the 5:2 diet is all about.


The core of the diet is that you can eat whatever you want a certain number of days a week, and then have a calorie restricted diet on other days. Now, when they says calorie restricted diet, they really do mean it. It should be 1/4 of your recommended dietary intake. For most people it roughly works out to be 500 calories for women and 600 for men. 

Scientific testing started out with Alternate Day Fasting (ADF), one day on one day off. However, they have found that you get most of the benefits from 5:2 - five days feasting and 2 days fasting. You lose more weight faster if you go up to 4:3 or alternate days, but still get some benefits if you do as little as 6:1.


The idea of alternate fasting has been around for ages. However, the 5:2 diet has became popular because of a BBC documentary by Dr. Michael Mosley: Eat, Fast and Live Longer, which came out in August 2012. 

The documentary is interesting as it is not looking at methods to lose weight, but at ways to prevent/reduce the effects of aging.

Dr. Mosley starts by looking at those who are on constant calorie restricted diets, eating around 3/4 of the recommended calorie intake on a permanent basis. This has been shown to have very good health side effects. However, I'm with Dr. Mosley when he argues that it might have great advantages, but he just can't see himself doing that all the time.

Next he looks at the advantages that have been linked to doing longer fasts, such as 3-4 days. These appear to allow your body to do some healing, but you need to do them every few months in order to maintain the effect. Dr. Mosley tries a 3.5 day fast and survives, but argues that the thought of trying to do that every few months is a bit soul destroying.

He then looks at the research into ADF, where subjects can eat whatever they like one day and then have 1/4 of their required calories the next. So, it's not true fasting, as you can still have something, but the research appears to suggest that it has all the same benefits as doing longer fasts. Further, most of the effect can be gotten by doing even less, as little as 2 days of fasting a week.

Dr. Mosley finishes the program by trying the 5:2 diet for 5 weeks. In that time he loses quite a lot of weight (20lb (9.7kgs) over 9 weeks), but also reduces his cholesterol and blood sugar (both of which decrease the risk of various diseases). He has since moved onto a 6:1 lifestyle, to maintain the health benefits but to stop losing so much weight. Now there's a problem I'd like to have!

The show is only an hour long, and I highly recommend you sit down and watch it all if you have the time. Annoyingly, most of the channels that hosted it have expired, but you should still be able to find a copy of the full documentary at

The Book:
After watching the documentary, Kate Harrison tried the diet and finding there was very little information, created the book: The 5:2 Diet Book, which further popularized the diet.

To be honest, I've just finished reading the book and it really is a lot of fluff. It is pretty thin to begin with, is puffed out with quotes and testimonies from other dieters, and really isn't as well set out at the documentary. It does look a bit more at the effects of the diet on mental health, which is interesting, and does have some recipes at the back which are useful. However, the recipes are pretty basic, and the 'ready meals' section is only useful if you live in the UK. Also, now that there are more recipes on the internet, you don't really need it.

If you are interested in the diet, I would highly recommend that you watch the documentary, and if you feel like you need more support, Dr. Mosley has written follow up books such as The Fast Diet.

The Weightloss Benefits:

Weightloss is supposed to be a side benefit of the diet, though for a lot of us (me included) it is one of the major reasons we are attracted to the diet.

5:2 Fast Diet forum has collected data from over 1,500 particpants for the first 6 months of fasting, and have made a very nice graph, which gives you a good indication of what you can expect weightloss-wise:


Based on their data, they have concluded that you can roughly expect:
- general weekly loss of around 0.45kg.
- a lot of people lose a lot of weight in the first week or two, but then plateau.
- if you're already in the healthy weight range, you're likely to lose weight more slowly.
- men tend to lose weight faster than women.

However, while this might not seem much compared to other fad diets, the big thing going for it as a method of weight loss is that on your feasting days you really can have what you want, with no guilt attached.

Researchers looking into ADF suspected (like most of us) that on the feast days participants would eat more than enough to make up for the restrictions the day before, so 175% of their required intake. However, they found that even with the opportunity to eat anything, the participants actually only ate 110%. Moreover, the research found that having a high fat diet on your feast days does not negate the effects of the fast days, so you really can eat anything you want.

It is also the guilty free part that appears for most people. Imagine what it is like to never have to worry, ever again, about eating that extra piece of cake, in exchange for just two days of fasting?

Further, as a lot of participants will tell you, the fasting days appear to 'reset' what you think of as a 'normal' amount, making you feel fuller faster on your normal days. 

Other Health Benefits:

The controversial part of the diet, however, is not the weightloss but the health claims. Researchers are suggesting that it can increase life span, improve blood sugar levels (reducing the risk of Type 2 diabetes), lower cholesterol, improve cognitive function and protect against dementia and the risk of Alzheimer's, as well as protecting against disease. Sounds pretty impressive, no?

Is it all good news?

One of the major criticisms of the diet is that there is just not that much research into it. Yes, the research that has come out has been promising, but more would need to be done in order to justify all the claims.

This is reflected in a lot of the rules which appear to be slightly arbitrary.  Is 500/600 calories really the best amount to get maximum effect? Is 5:2 really just as good as ADF, or should everyone be doing alternate day fasting to get the promised results?

An interesting article which looks at some of the research around Intermittent Fasting was published by the NHS on the 5:2 Diet, questioning its claims. If you are interested in the research side, it is a good place to start.

The article is written from a skeptical point of view, and even then they could only conclude that there wasn't sufficient evidence to support all the claims. They couldn't find any evidence against it.  


If you have never fasted before, the first few times can be a bit scary. You just don't know what to expect, and fear that you are going to be swallowed up by a growing hole in your stomach. Surprisingly, this doesn't happen, though you can be a bit grumpy.

It does take some getting use to how much 500-600 calories really is. You will need to carefully calorie count for a while, or eat ready meals that have already been worked out for you.
Most processed food is out, and to get as much bang for your buck, you really do need to focus on veggies, lots of veggies.


As with all diets, there are certain people that should get medical advice before trying this, particularly pregnant women and those who already suffer from eating disorders.


If you are looking for a long term plan that will require very little change to your current lifestyle, and allow you to eat what you want most of the time, and yet still lose weight at a sustainable pace, this diet has a lot going for it. It is amazingly flexible and leaves you feeling guilty free the rest of the time. It doesn't require any expensive/weird tasting food and doesn't make you anti-social most of the time.

If the science also proves to be correct and it protects against a lot of the problems of old age, that for me is an added bonus.

When you are struggling on your fast days, just keep this motto in mind:

I can eat anything I want... tomorrow. 

the fast diet
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