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Technician Lucy returns to the pharmacy after her lunch break with a magazine in her hand and a puzzled look on her face...

“Can you help me get my head round this please?” Lucy asks pharmacist Parveen. “I’ve been reading in this magazine about something called 16:8 eating. Is it the same as the 5:2 diet? But that would mean that you eat for 16 days then fast for eight. It’s so confusing!”

Answer

The 16:8 diet involves restricting eating to an eight-hour window each day and rose to fame when a book entitled ‘The 8 Hour Diet’ was published last year. The author makes many claims about this way of eating, but there is little evidence supporting such an approach to weight loss.

One study in mice suggested that feeding times influenced metabolism, and while another paper pointed towards a combination of calorie restriction, exercise and intermittent fasting as a way of reversing some of the changes caused by ageing, the research team agreed that more work needed to be done to explore exactly what regimen of eating and fasting works best.

The truth of the matter is that restricting the time during which someone can eat to just eight hours a day tends to limit the amount of calories that they consume. By only eating between the hours of, say 2-10pm each day, the individual will miss breakfast, and have a late lunch meaning they are more likely to eat a smaller dinner. Ultimately, if the number of calories being taken in is exceeded by the calories being used up, weight loss will result.

The bigger picture

Intermittent fasting hit the headlines when the BBC screened a Horizon documentary on the topic in 2012. The 5:2 diet quickly became popular because it is much more straightforward than many weight loss plans: eat normally for five days a week, and fast for the other two days, which must not run consecutively. The fasting days involve restricting calorie intake to just 500 per day for women and 600 for men.

There is evidence supporting the health benefits of the 5:2 model. A 2010 study found that this way of eating achieved similar levels of weight loss as a more general calorie controlled diet, and there was a decrease in a number of biomarkers, which point towards a possible reduction in the risk of developing conditions such as type 2 diabetes. A 2012 study found that there may also be a reduction in the risk of developing breast cancer.

However, much of the success of the 5:2 diet has been attributed to the simple fact that fasting helps people relearn what it feels like to both be hungry and full. This, in turn, makes people more aware of what they are eating on non-fasting days. Most people who follow the 5:2 diet experience a net decrease in calorie intake over the week.

Extend your learning

• Find out more about intermittent fasting at NHS Choices.