The 5:2 Diet: Not All It's Cracked Up To Be

In the last year or so, the 5:2 intermittent fasting diet has become so well known that it has been written about in most magazines and nutrition blogs, been the subject of several television programmes and has many books written about it. It is a diet based in the principle of intermittent fasting: you eat ‘normally’ for five days and you fast for two days of the week. Intermittent fasting came to most people’s attention when it was featured in a BBC documentary in August 2012: ‘Horizon: Eat, Fast and Live Longer’. In this documentary Dr Michael Mosely investigated intermittent fasting and tried living on the diet himself, discovering many aspects of his health improved and his weight reduced in the process.

Michael Moseley and his 5:2 sidekick, Mimi Spencer.  

On the 5:2 intermittent fasting diet you ‘fast’ for two days of the week, eating only 500-600 calories per day which is essentially just another way of reducing the total calories consumed per week. On 'normal' days, you eat, well, normally. So if you're a woman you stick to 2,000 calories and if you're a man you stick to 2,500 calories. The official Fast Diet website describes the five 'normal' days as "days of normal eating, with little thought to calorie control and a slice of pie for pudding". Call me cynical but I would suspect that if a person is overweight - hence they began the diet - it is their  "normal eating, with little thought to calorie control" that lead to them being overweight and therefore needs addressing. To encourage this is not only irresponsible but dangerous, as we all know the consequences of being overweight (heart disease, stroke, Type 2 Diabetes). It also bothers me that there is absolutely no thought given to those people who are overweight because of a negative relationship with food or even an eating disorder such as compulsive overeating disorder. This is a genuine disorder with debilitating effects, not just physically but emotionally and psychologically. It is so important that a person is supported emotionally as they work on reducing their weight, and that they aren't just left to tick boxes and follow instructions to "eat normally" and then starve.

This diet is also a danger for sufferers of other eating disorders, namely anorexia nervosa and bulimia nervosa. As we know this diet encourages a cycle of starving and (potentially) gorging, much like the binge-purge cycle of bulimia, and sometimes of anorexia. The 'fast' days, in encouraging such severe calorie restriction, could easily trigger even a recovered anorexic or bulimic person. I would recommend so, so strongly that if you have ever suffered from an eating disorder, have a negative relationship with food or have a history of comfort eating or food restriction, that you don't touch this diet with a barge pole.

So let's go back to the weight loss people experience on the 5:2 diet. An average woman who requires 2000 calories per day and is on the 5:2 diet is simply reducing her weekly calorie intake from 14,000 to 11,000 which is likely to affect her weight in the same way that reducing her daily calorie intake from 2000 to around 1600 (seven days a week) would; it equates to the same calorie deficit. This creates a weekly calorie deficit of 3000 calories, equating to just under 1lb of weight loss per week. Most doctors, dieticians, nutritionists and sensible weight loss diets will tell you to consume around 1,600 calories per day (if you're a woman - 2,000 if you're a man). This creates a weekly calorie deficit of 3000 calories, equating to just under 1lb of weight loss per week. Nothing new: reduce your calorie intake by 3,000-3,500 and lose a pound in weight. 

The weight loss experienced during intermittent fasting depends on not overeating on the five remaining ‘normal’ days of the week. In this respect, the 5:2 diet offers nothing new or miraculous, it is simply a method of reducing calories. It may feel tempting to reach for the biscuit tin after two days of restrictive eating, your body will certainly be screaming out for an energy quick-fix as it slips into starvation mode and the metabolism slows down. However it is vital - if you really must follow this diet - that you don't binge eat or eat sugary, high-fat, refined and processed foods on your 'normal' days. The idea is that you eat a wholesome, healthy diet full of wholegrains, protein, healthy fats, natural sugars and plenty of fresh fruits and vegetables, which is great, until day six comes around and you have to starve yourself. However for people who struggle to diet 24/7, having to only restrict calories twice a week may be an ideal option.

Research has shown that intermittent fasting is just as effective as constant calorie restriction in terms of weight loss, insulin sensitivity and other health risks such as heart disease and high blood pressure (Harvie et al., 2010). Previous to the 2010 study led by Dr Michelle Harvie, the benefits of intermittent fasting had only been tested on rodents yet showed equal – sometimes more – effectiveness than constant calorie restriction with regards to weight loss and reducing disease risk. Harvie’s experiment involved prescribing a 25% calorie restriction diet to two groups of women over six months: one group was intermittently fasting, the other was constantly restricting calories. Harvie found that the women who intermittently fasted lost more body weight than those who constantly restricted and fat loss was the same for both groups, demonstrating that intermittent fasting could be an ideal diet for anyone who struggles to stick to a constant calorie restriction diet.

In Harvie’s experiment, intermittent fasters experienced greater improvements in insulin sensitivity, greater reductions in insulin resistance and a greater increase in adiponectin (a protein involved in the regulation of blood-glucose levels and fatty acid breakdown which, in higher quantities, can aid weight loss) compared with constant calorie restrictors. Other research suggests that along with these benefits, intermittent fasting can increase lifespan, improve cognitive function thus protecting from conditions such as dementia and Alzheimer’s, and protect from diseases such as heart disease (NHS, 2013). However, the NHS propose that currently there is not enough detailed research into the 5:2 intermittent fasting diet to understand how exactly these benefits occur. For example, although the 5:2 diet recommends women eat 500 calories and men eat 600 calories on fast days, there is no evidence offering good reasons for these specific figures. Equally, it is unclear whether 5:2 fasting is the most beneficial form of intermitting fasting – it could instead be alternative day fasting, for example. Also, as the 5:2 diet has only been popular for around 18 months, its sustainability in the long term is currently unclear (NHS, 2013).

On Horizon’s ‘Eat, Fast and Live Longer’, Dr Michael Mosely discovered that by consuming only 600 calories per day on his ‘fast’ days twice a week and eating his normal diet on his ‘feed’ days, for a total of five weeks, he lost a stone in body weight. He also found his blood markers such as IGF-1, glucose and cholesterol improved which will, in the long term, reduce his risk of age-related diseases like cancer and diabetes (BBC, 2012). Mosely also found that by eating a balanced 300 calorie breakfast to kick-start his ‘fast’ days, he would have adequate energy throughout the day and would not feel the need to binge, even on ‘feed’ days.

It is evident that the 5:2 intermittent fasting diet has some benefits, particularly to people who can stick to a healthy, well-balanced diet on 'normal days' and are not easily triggered into a binge-purge or binge-starve cycle. And as Michael Mosely discovered, there are some other health benefits to the 5:2, although nothing that a balanced diet 7 days a week wouldn't also produce. It appears to be an ideal diet for people who have struggled to be on a diet 24/7 before, as calorie restriction only takes place on two days per week. What seems to make this diet more sustainable for most people is the fact that you are never more than one day away from eating ‘normally’ again. But is this not just another diet which pulls us back into the cycle of trying one fad diet after another, overeating, undereating, cutting out food groups, making up for lost calories, restricting, guilt, weight gain, weight loss, repeat?  

 P.S. Michael Moseley trained as a doctor and went on to work at the BBC as a trainee producer. He's since made several science and history documentaries. Mimi Spencer, co-author of The Fast Diet (the 5:2 instruction manual) is a journalist who "writes on women's and lifestyle issues", according to hers and Michael's website (TheFastDiet.co.uk). Neither seem to have worked in, or trained in, nutrition, yet they have somehow managed to revolutionise the way many people think about food and dieting. That's some very good PR. 

References

Harvie et al., 2010, ‘The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomised trial in young overweight women’, 5 October 2010, published by Int J Obes (Lond). http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3017674/

NHS, 2013, ‘Does the 5:2 Intermittent Fasting Diet Work?’, NHS Choices, January 2013. http://www.nhs.uk/news/2013/01January/Pages/Does-the-5-2-intermittent-fasting-diet-work.aspx

BBC, 2012, ‘The Power of Intermittent Fasting’, 5 August 2012, http://www.bbc.co.uk/news/health-19112549