The other day a friend asked me what I thought of the 5:2 diet. Like so many of us at this time of year, he had been reflecting on the past and was wanting to make a fresh start. He was starting to make some new goals for the new year ahead and slimming down was one of them. He wanted to know if the so called ‘fast’ diet would work.

The 5:2 diet became popular with thanks to the endorsement of British doctor and BBC presenter Michael Mosley. The idea is that for five days of the week dieters eat as they normally would but on the other two days, they restrict calories to 500–600 per day. In other words, if you starve for two days of the week, this part-time diet allows you to have your cake and eat it too. No wonder it has appeal.

Because the research I do is thorough, I’m hesitant to write about the pros and cons of specific diets. (I’m the kind of person who sets out to write a simple blog post about Omega 3, only to emerge three weeks later after reading three books and dozens of academic papers, as well as interviewing two leading scientists). But I couldn’t help myself, and for this blog post I did start to look into some of the recent research on fasting diets. For example, this 2016 study found that a fasting diet was as effective for weight loss as the ‘heart healthy diet plan,’ which met the guidelines recommended by the American Heart Association. The study also found that those on the fasting diet were more likely to keep the weight off after one year.

But I had to stop myself at just this first study, because as always with nutrition science, it’s the detail that really matters. Although it did have promising results, when you look at what the people who lost weight actually did, there was much more to it than the ‘easy’ 5:2 diet plan my friend was thinking about trying.

For the first 12 weeks, the 40 obese men and women in the study mostly consumed liquid meal replacements 4–5 times per day, for six days of the week. On their one ‘fast’ day, they essentially consumed very little and took various multivitamin and herbal supplements. The participants also had weekly meetings with a registered dietitian and were given detailed written and verbal instructions. They kept a food diary and their special meals were easy to prepare and provided for them. Unsurprisingly, they lost weight.

My point here is that in this study, 40 men and women followed a very particular program that involved several different components including easy pre-packaged foods, regular expert follow up, self accountability through a food diary etc. To think that this study provides evidence that skipping meals twice a week will work for every person, of every age, in every circumstance, for the rest of their lives is oversimplification at best, and misleading at worst.

There’s also another significant piece of information buried in this study that I think is actually the key take away message for anyone who’s thinking about making healthy changes in their lives – whether it’s going on a diet, starting an exercise routine, or a daily meditation habit. The key is to do something you’ll stick to in the long run. While 40 people completed Phase 1 (the first 12 weeks) of the study, only 24 people went on to Phase 2 (the following 12 months where they chose the fast diet or the heart healthy diet plan). Even more significant is the fact that those 16 people were all excluded due to drop-out and non-compliance. In other words, even with all that support, people found that being on a diet was really really hard in the long run.

This reminds me of a huge meta-analysis (a study of studies) that was performed by Canadian scientists in 2014. They wanted to figure out which diet works best for weight loss. They looked at 48 randomised control trials that included data from more than 7000 people who had tried various big brand diets. Their conclusion? “The weight loss differences between individual named diets were small with likely little importance to those seeking weight loss.” In plain English – Which is the best diet for weight loss? The one you’ll stick to.

I’m not surprised by these findings. When my friend asked me about the 5:2 diet, I told him about an interview I did a couple of years ago. During the interview the person I was filming, who was known to be great talent on the topic she’s an expert in, kept trailing off and forgetting what she was trying to say. An interview that should have taken about 30-45 minutes turned into hours. By the end she was practically incoherent. It turned out, she was on the 5:2 diet and I had caught her on a “2” day. Her stomach was doing all the talking that day, and it was saying “feed me.”

According to the UK’s National Health Service there are other anecdotal reports of side effects from fasting including:

    •    difficulties sleeping
    •    bad breath
    •    irritability
    •    anxiety
    •    dehydration
    •    daytime sleepiness

I know my friend pretty well and I know that like me, he suffers from a terrible affliction called the hangries (a powerful combination of hunger and anger that I’ve written about previously and can leave tornado-like devastation in it’s wake), so it will be an interesting experiment if he does goes through with the new diet.

With all of this in mind, I told him what I tell anyone else who will listen – one of the keys to making healthy changes last, regardless of whether you’re wanting to completely shake up your diet, start a regular meditation practice or exercise routine, or even quit an unhealthy habit, is that you have to think about it as a "forever thing". I suggest trying this two step process: Step 1: Ask “Is this something I would do even when I’m on a holiday?” If the answer is yes, then proceed to Step 2.