The risks, guidelines and benefits of the 5:2 fasting diet

Diets come and go, but occasionally one will come along that attracts multitudes of passionate advocates, all proclaiming its benefits. The 5:2 diet – which simply entails easting normally for five days a week, then eating no more than between 500 to 600 calories on each of the next two days – goes even further. Fans of the 5:2 say it can help slow the ageing process and prevent disease, as well as making the pounds drop off. As with many diets, convincing scientific evidence is scant, but that’s not to say there haven’t been some studies suggesting a link between intermittent fasting – or IF – and the above claims. Champions of the diet say you can easily lose around half a kilo (one pound) a week on the diet.



For five days there aren’t many guidelines as you simply eat as you normally would. The difficulties you will have are making sure you stick to the 500 (if you’re a woman) or 600 (if you’re a man) calories for the two days of fasting. The two days should not be one after the other. You will have to be prepared and do some research on menu ideas and the kinds of foods – and the amounts – you can eat while you fast. Luckily, because of the popularity of the diet, plenty of people have prepared such recipes.

Types of food Keen 5:2ers recommend eating fruit, vegetables and protein on your fast days. Avoiding things with refined sugars and carbohydrates will keep the calorie count low. People talk of the “plants and protein” motto for these days, and it is wise to have this in the back of your mind and stick to this as much as possible. Calorie count

A simple internet search for 5:2 recipes will yield many and varied options for menu ideas – each with their own individual calorie counts. Variety can be key to maintaining any diet, so don’t just stick with the same boring things to keep you interested. You should soon have a repertoire of meal options that you instinctively go for on your fast days. Plan ahead

Make sure you have the right things in the house when your fast day is coming up. Include the low calorie items in your usual shop rather than going out specially for them. Make buying them second nature and save them for your fast days. If you run out of calorie-light options, you may be tempted to justify breaking open the biscuit tin because you “had no choice.” Flexibility

Don’t panic if you go 10 or 20 calories over your calorie count on your fast days, but don’t let it slip too much or too often. The figures of 500 and 600 are about a quarter of what you should normally be eating, so these aren’t set in stone. It can be helpful, however, to have firm goals that you aim for on each fast day.


Flexibility (again) Because the diet is intermittent, there is plenty of light at the end of each day-long tunnel for the dieter. You can still have your treats on your five normal days and won’t have to give anything up. You are able to choose your two fast days each week, so this can fit in with a changing schedule, like meals out, parties and Christmas Day.

The pounds Quite simply, weight loss. Many people say they’ve tried lots of different techniques for weight loss, but the 5:2 is the only one that’s worked. When we fast intermittently, the body releases SIRT1 – a gene that inhibits fat storage. This is good news for those wanting to shed the flab.

Anti-ageing The SIRT1 gene may also help slow the ageing process and improve brain function, reducing the likelihood of suffering Alzheimer’s. These are big claims, and the only tests so far have been on mice, but future research on humans is planned. Watch this space.

Disease prevention Another claim of the 5:2 advocates is that it cuts the risk of heart disease, diabetes and some cancers, but this can also be said of anything that helps you lose weight, since the above are all linked to obesity. All of the above claims have been questioned by many medical professionals, including the NHS, because of what it says is a simple lack of evidence.


Fasting When fasting by eating just 500 calories (600 for men) in one day, there is a risk you will become tired, weak and lack concentration. This can effect your work, and especially if you are tired, the safety of things like driving. If you have a physical job or one that requires a lot of concentration, this might be a problem, so take it slow and see how it goes.

Exercise If you take daily exercise – and lots of people wishing to lose weight do – you may be less capable of it during your fast days, because of the reduced nourishment. Interrupting your exercise regime for the sake of fasting may do more harm than good if you want to stay healthy.

Over-compensating Fasting for two days a week may be very difficult for some people. If you experience a constant hunger on your fast days you may be more inclined to overeat on the other five days. Over-indulging this often can, of course, have negative effects on health – including actually gaining weight or eating the wrong things, such as sugary or fatty foods. People who advocate the 5:2 diet say your success will depend on you not overeating on your “normal” days. Failure

There is of course always the risk that the diet simply won’t work. This may depend on how you react to the fasting and how you then approach food on the other five days. The fasting element is clearly the crux of the diet and while cheating a little on another kind of diet may not have a massive effect on success, ruining a fast day could have big effects on the success of the 5:2. Some people have said it only really works if you have a lot of weight to lose, but this has been challenged. Other effects

The NHS says anecdotal reports of side effects of the 5:2 diet also include sleeping difficulties, irritability, bad breath, dehydration and anxiety. However, it also says a lack of study into intermittent fasting means this is unconfirmed and the potential severity of these is not established. It recommends talking to your doctor before embarking on what it calls “a fairly radical approach to weight loss.”

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About the Author

Robert Macintosh is a full-time journalist based in Northern Ireland. He has accumulated eight years’ experience since 2005, writing for magazines, newspapers and websites in various countries. Macintosh has specialised in politics and entertainment. He has an honours degree in social anthropology, an NVQ level 4 in newspaper journalism and an AS Level in photography.