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A Nutritionist's View of the 5:2 Diet

Intermittent fasting, more commonly known as the 5:2 diet, is a bit of a hot potato at the moment so to try and put your minds at rest, we've asked our nutritionist, Janet, to write an article on the diet, and it's pros and cons.

What's all the hype about?

In August 2012, a BBC Horizon documentary called 'Eat, Fast and Live Longer' pushed the 5:2 diet into the limelight. Presented by Dr Michael Moseley (a journalist with a medical background), the programme showed how following a process of intermittent fasting resulted in weight loss, and a reduction in certain risk factors such as blood pressure, cholesterol levels and blood glucose readings. The premise of the programme was that this was a new way of dieting, and a solution for anyone at higher risk of heart disease, diabetes and possibly even conditions such as Alzheimer's.

The 5:2 diet is actually pretty straightforward - you eat normally on five days of the week, and fast on the other two days.

Calorie intake on fasting days is recommended as 500 calories for women, and 600 calories for men, however these figures are arbitrary and don't take into account differences between individuals. On the 'normal' days there is no restriction on calorie intake or types of foods that should be consumed - for some this is seen as a great way to diet... having 2 very restricted days, and then 5 days of eating basically what you want.

What is the evidence for intermittent fasting?

There is no doubt that, in the study shown on the BBC programme, there were marked changes in Dr. Moseley's body, both internally and externally, however this 'study' was only based on one individual. Unfortunately there is not enough good quality, long term evidence to say whether following a 5:2 diet is beneficial or harmful.

The basis of the 5:2 diet is actually from clinical trials carried out into the effect of diet on breast cancer risk by Dr Michelle Harvie, and colleagues, at Genesis Breast Cancer Prevention. Dr Harvie, a registered Dietitian, wanted to find an innovative way to encourage weight loss in her study participants. The original version of the diet is called the Two Day Diet, and followed a less intense approach - this is more about calorie restriction over the period of a week, rather than just focusing on the benefits of fast days. Dr Harvie's method is to have 2 'fasting' days of up to 650kcal, then 5 days following a healthy and balanced meditteranean diet of around 1900kcal. The diet used in the clinical trial has been written up in a book (www.thetwodaydiet.co.uk). Despite clinical trials using this form of intermittent fasting, the researchers describe the limitations of small study sizes, and no long term follow up trials.

Nutracheck's position is that a weight loss programme must be supported by medically recognised evidence. Weight loss shouldn't be something that is a quick fix - it should be a lifelong change in attitude and habits, resulting in a healthier person forever. The current lack of evidence for the 5:2 diet means that it's not something that we can support, however we will of course be keeping an eye on emerging science in case anything changes on this front.

What if I still want to try it?

The general interest in 5:2 dieting has led to us being asked whether we can offer a way of fitting fasting days into our food diary model. The simple answer is that at the moment we don't support this way of losing weight due to the lack of evidence. However if it something that you think might work for you, then using the food diary to make sure you're getting the right level of calories on your fasting days would be a sensible approach.

500/600 calories isn't very much and it's important that you get good quality nutrition from what you do eat on your fasting day- fill up on plenty of vegetables and fruits, seeds and grains, small meals such as scrambled eggs with ham, chicken salad or grilled fish plus plenty of water, with some herbal tea or black coffee to drink.

On non-fasting days the theory is that you can eat what you like, however still use your food diary to make sure you're not going too mad! Stick to the principles of healthy eating too, and don't slip back into bad habits.

If you do try intermittent fasting, it's probably best to use it as a short term kickstart to a more sensible weight loss/ maintenance programme. Talk to your GP or practice nurse before you embark on any change in your diet, monitor your progress and how you feel every week, and only follow the diet for a maximum of 8 weeks.

What should I watch out for?

Because of the lack of evidence to support the 5:2 diet we don't really know what the long term effects of fasting might be. There may well be many positive benefits, however there may also be negative effects too. If you do choose to follow this diet then you need to be very aware of your body, and how you are feeling. There is some thought that this type of diet may be attractive to people who are prone to disordered eating so it's important that you don't become addicted to the fasting days, or the feeling of being hungry.

Exercising may also be an issue on fasting days - if you are someone who exercises a lot, this may not be the right plan for you. 500/600 calories is not enough to maintain you through a gym session or exercise class, so just be careful about what activities you choose.

The final word

The 5:2 diet is an interesting concept, and certainly one that we are keeping a watchful eye on, however there isn't enough long term evidence to show that it is a safe, and healthy, way to lose weight. If you choose to follow a 5:2 diet under your own steam, then using Nutracheck's food diary may help you to get the right number of calories on fasting days, and keep a check on calorie intake on non-fasting days. The key to doing this right is to know your own body, and be aware of any changes that are unusual or worrying. Always contact a healthcare professional before embarking on any kind of weight loss plan.


You are advised to seek medical advice before making any changes to your diet or lifestyle with an aim of weight loss. This website and the content provided should not be used by persons under 18, by pregnant or nursing women, or individuals with any type of health condition, except under the direct supervision of a qualified medical professional. The information contained in these articles, and elsewhere on this website, is provided for educational and entertainment purposes only, and is not intended to replace, and does not constitute legal, professional, medical or healthcare advice or diagnosis and may not be used for such purposes. Continue...