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5:2 diet – facts & myths

Last Updated: 15 January 2019








5:2 diet – facts & myths

Is the 5:2 diet really the miracle diet it’s promised to be? Here are our expert thoughts on the pro’s and con’s of the fast growing diet plan.

Ever since Michael Mosley’s BBC documentary came out, the world has gone crazy for the fasting diet (otherwise known as the 5:2 diet). 


The basic rules are that for two days a week you eat no more than 500 calories for women or 600 calories for men. The rest of the time you can eat whatever you like, although it is recommended that you stick with a ‘normal’ diet. But is this diet effective and easy to stick to over a long period? Lets take a look:


  • Easy to stick to (particularly for those who eat out or travel a lot)

  • Evidence suggests that intermittent fasting may improve health markers such as blood glucose control, levels of cholesterol and blood pressure.

  • A few studies have shown good rates of weight loss, though it is unknown whether this weight loss is long lasting.



  • The 5:2 diet doesn’t promote a balanced way of eating. Instead, it promotes a ‘binge, purge’ mentality.

  • On fast days, it’s unlikely you’ll be getting the range of vitamins, minerals and other nutrients needed for your body to function at its best.

  • It’s not recommended for anyone who exercises intensely, pregnant or breast feeding women or anyone with a health condition.

  • Evidence suggests that the fast days could reduce levels of a hormone linked with fertility in women. 2

  • Common side effects include headaches, nausea, constipation, sleep problems and low energy.


The verdict

Most dietitians and nutritionists would not recommend the 5:2 diet as it does not promote a healthy, balanced way of eating. Like any fad diet, it may be difficult to sustain in the long term. As this way of eating is relatively new, there's also little strong scientific evidence of the benefits of indeed possible long-term side effects. If you are looking to lose weight, it's recommended that you focus on a diet low in saturated fats, high in fibre, and one that includes unrefined carbohydrates, lean protein and some essential good fats every day.


Written by Ruth Tongue

(MSc Nutrition)



Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Varady et al. American Journal of Clinical Nutrition 2009 Nov, 90(5): 1138-43
The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomised trial in young overweight women. Harvie M et al. International Journal of Obesity.

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