“So I need a new diet plan. I’m just not able to stick with my current one. It’s too strict.”
“Okay so how about just stop eating all the pizzas, takeaways and cakes you usually have and maybe add some more vegetables to your diet?”
“Right, okay, that all sounds rather demanding. So how long would I have to do that for?”
“Erm, every day. And always.”
“What do that every day? No that’s impossible, I know what I’m like, I can’t do something like that forever. Is there no way we could adapt the diet? Maybe make the timeframe smaller, and in return the changes a bit bigger?”
“Okay, so how about every second day you eat a lot of vegetables and whole foods and don’t eat any junk food or chocolate treats all day?”
“Every second day? Are you mad? That’s more than half the week! No that’ll never work. It still needs to be smaller. Like I said before I’m happier making bigger changes, as long as it’s for a shorter period of time.”
“Okay how about twice a week you fast and the rest of the time you just eat normally?”
“Fast? You mean eat nothing at all? All day? That’s physically impossible. Are you trying to kills me? Can I not have a little something, just to tide me over?”
“Okay, how about 600 calories?”
“Done, now would it be possible to spread them out over x2 meals only I’ll get hungry otherwise”
… and so in my mind the popular 5:2 diet was born. A diet borne out of a refusal to make sensible and measured changes and instead a desire for a quick, no-thinking-required answer.
In short the perfect 21st century diet.
Annoyingly the diet was actually created by Dr Michael Mosley in his 2012 BBC Horizon programme. Since then there have been a wealth of copycat and vaguely similar diet plans and now there are hundreds of books to choose from on the subject.
But back when Mosley stumbled upon it he said he was looking for the least intrusive diet he could find.
While I've known about this diet for years I've always been a little hesitant to back it because the plan seemed to fly in the face of sports science and the advice that's been handed out for years.
According to sports science one of the reasons people were getting fatter was because they were eating too infrequently. Three meals a day meant peoples’ blood sugar levels were dropping then soaring which pushed blood glucose into fat cells. The answer was to eat less but more frequently. Six meals a day was the answer if you wanted to lose weight.
And yet the evidence for fasting or Intermittent Energy Restriction (IER) – be it Mosely’s 5:2 fast, Alternate Day Fasting or some other variation – is really quite compelling. So when I was assigned the 5:2 diet as part of my nutrition course I thought I'd read up on it, give it a go, and write a little something on what I found out.
One of the problems with the diet is that it still relatively young – if you ignore wandering around in the desert for 40-days or other religious versions – and therefore there isn't an abundance of studies into the diet, but what we do have is really quite positive.
In her 2010 study British fasting expert Dr Michelle Harvie found that intermittent fasting was as good as general calorie restriction for reducing leptin, total LDL cholesterol, triglycerides, blood pressure as well as increasing levels of sex hormone binding globulin and IGF proteins 1 and 2. There were also modest reductions in both fasting insulin and insulin resistance. (all these change being generally rather good)
Harvie later found that intermittent fasting potentially lowered the risk of obesity-related cancers such as breast cancer.
In a more recent study another fasting expert Dr Valter Longo concluded that animal studies have “documented robust and replicable effects of fasting on health indicators including greater insulin sensitivity, and reduced levels of blood pressure, body fat, IGF-I, insulin, glucose, atherogenic lipids and inflammation.”
Longo also found that fasting regimens “can ameliorate disease processes and improve functional outcome in animal models of disorders that include myocardial infarction, diabetes, stroke, AD and PD.”
Longo put these benefits down to fasting’s abilities to “trigger adaptive cellular stress responses, which result in an enhanced ability to cope with more severe stress and counteract disease processes.”
Additionally he contends: “by protecting cells from DNA damage, suppressing cell growth and enhancing apoptosis of damaged cells, fasting could retard and/or prevent the formation and growth of cancers.”
Some have argued that the positive effects seen with fasting can be attributed to simply the general restriction of calories. With a reduced calorific intake comes weight loss and with weight loss comes a raft health benefits.
Others say that this thinking has things the wrong way round and that the weight loss and the improved health markers are actually because of the act of fasting.
Dr Jason Fung believes it is the effects of the diet on insulin and insulin resistance is the real benefit of intermittent fasting.
He says: “The short answer is that the beneficial hormonal changes that happen during fasting are entirely prevented by the constant intake of food.”
Referring to Harvie’s study Fung points out: “there is a clear, substantial improvement in insulin levels favouring the IER (intermittent energy restriction) group. Even more impressive is the change in insulin resistance.
“In the CER (constant energy restriction) group, there is virtually no change in their insulin resistance (IR). Because there is no change in IR, this will continue to lead to higher insulin levels in a vicious cycle. These higher insulin levels perpetuate the higher IR.
“This is the long term problem of weight loss. This is exactly the part of the equation that is typically ignored and leads to the typical weight regain. It is the intermittency of the diet that makes it effective.”
It is worth pointing out that both Harvie and Longo note that studies have so far focussed mainly on overweight people and so the jury whether IF can be recommended to the entire population is still out. Indeed the NHS still doesn't recommend the diet citing a lack of evidence behind it.
Interestingly there are splits within the fasting camp itself. Dr Krista Varady, one of the IF experts Dr Mosley uses to substantiate his diet, demand Mosley remove her work from his book after claiming that there is no direct evidence in favour of the 5:2 diet and that her studies show the real benefit of fasting comes only when it is applied every other day.
Varady says: “My research on alternate-day fasting has been misrepresented in [Mosley’s] book. Mosley used my research, which looks at fasting three to four days a week, to support his diet, which encourages fasting two days a week.’
“The Fast Diet is about his experience, but unfortunately he actually used all of my research on alternate day fasting to support all of his points. Scientifically you can’t take studies that look at three or four days fasting a week like mine and say it’s the same thing and that you’re going to get the same health benefits when you just fast two days a week.”
When we consider both Varady and Mosley have diet plans and books to promote this squabbling doesn’t appear so surprising.
Then there are also those who suggest that the 5:2 diet is actually an unhealthy diet.
In an experiment on mice, researchers at The National Institute of Nutrition and Seafood Research (NIFES) in Norway, found that mice who were subjected to intermittent fasting while having access to obesity-inducing diet i.e those who were allowed to pig out on non-fasting days, put on more weight than those who didn’t fast but had access to the same diet.
Even Fjære, a researcher in the study said: “This study shows that the development of obesity is not merely due to the total energy intake as such. When we eat and how we divide up our meals are also decisive factors,”
"We may well ask what will happen when the trend ebbs out. It is not unthinkable that this slimming fad will just lead to more obesity and related illnesses, but it is still too early to say,” says Fjære. 
Additionally despite many suggesting that fasting allows you to eat whatever you want on the days you’re not fasting Varady say that this isn’t true and that it’s not solely how many calories you eat but from what source that is important.
In fact on the BBC GoodFood website those considering the diet are recommended to: “make sure that your non-fast days are packed with nutritious options, including fruit, veg, wholegrains and lean protein such as chicken, fish, turkey and dairy foods.”
I’d argue that if people spent five days a week eating lean proteins, vegetables and fruit then they probably wouldn’t need to be looking at losing weight by fasting.
So should you go on the 5:2 diet or some other form of fasting? I've given it a shot a few times and I'll be honest the hardest part is the mental fear that grips you the night before when you think of not eating the next day.
But once you get up and going and make sure you have plenty of water in your the hunger pangs aren't actually that bad. And you're generally surprised how much extra time there is in a day when you don't have to worry about making food or eating.
More importantly I did find that I lost weight and on my non-fasting days didn't feel the need to binge to make up for lost calories.
 The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Harvie MN, Int J Obes (Lond). 2011 May;35(5):714-27. doi: 10.1038/ijo.2010.171. Epub 2010 Oct 5. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3017674/
 Valter D Longo and Mark P. Mattson Cell Metab. 2014 Feb 4; 19(2): 181–192.