– by Dr Rachel Cheatham


Say the words intermittent fasting and it conjures up thoughts and images of near starvation that may or may not produce weight loss. Thanks though to the popularity of the Fast Diet which started in the UK, there’s a growing interest in what’s known as the 5:2 approach. That’s shorthand for eating normally five days a week and then fasting the other two.

A research study called the Effects of intermittent and continuous calorie restriction on body weight and metabolism over 50 wk: a randomized controlled trial took a deeper look at this 5:2 approach. The scientist in me jumps for joy when I see that it’s a 50-week randomized controlled trial (or RCT). No human study of this type has been conducted for that duration. Also, RCT is the gold standard for trial design. It’s definitely time to take a closer look!

The Study Deets

Study participants included 150 overweight and obese men and women who were randomly assigned to one of three groups:

  1. ICR – Intermittent calorie restriction where participants eat 5 days without energy restriction and then 2 non-consecutive days where they eat only 25% of their regular calorie amounts.
  2. CCR – Continuous calorie restriction where participants cut their calories by 20% on a daily basis.
  3. Controls – Because someone has to eat like normal!

The key is both the ICR and CCR groups end up consuming 80% of their normal energy requirements, meaning they both cut 20% of calories. The difference then is really more about whether or not these two calorie-cutting approaches yield distinct outcomes.

Speaking of outcomes, the researchers defined their primary one as ‘diet-induced changes in metabolic function.’ These include various parameters like weight loss, body fat changes, glucose/insulin control, hormonal changes, and immune function, along with the expression of 82 metabolically-relevant genes.

On the timeline front, the study was divided up as follows:

  • 12-week intervention phase
  • 12-week maintenance phase
  • 26-week follow-up phase

To be clear, the active portion of the study where the participants had comprehensive dietary counseling from dietitians (which included phone support, suggestions, and encouragement) was really only 3 of the 12 months. This means the majority of the time the participants were on their own. Not an ideal intervention in terms of ongoing adherence, but at least the researchers were able to check in nearly a year after the start. The longer-term duration is arguably the most notable strength of this study.


The Study Results

The not-so-highly scientific way of reporting these results is to simply say ICR and CCR yielded similar results. There was slightly greater weight loss with ICR than with CCR (-7.1% weight change vs – 5.2%). Beyond this small difference though, all the markers tracked over the 50 weeks were essentially the same for ICR and CCR. This created tongue-in-cheek apologetic headlines that highlighted the so-called disappointing results.

But hold up! Why is it disappointing to learn that a) calorie restriction does work and b) there’s more than one way to go about it?

Let’s be real. Most of us don’t want to cut calories today, tomorrow or any day, but at least we’re learning there’s more than one way to go about it. It’s about the individual. For me personally, I find it hard to somehow subtly cut out 20% a day, every day. However, I’m also not much for the 5:2 idea. I just don’t like the premise of going a whole day with a mere 500 calories. I’m active daily and I find it difficult to do so in the absence of incoming fuel. …and, side note, the CCR group showed no changes in physical activity-associated energy expenditure, whereas the ICR group displayed a -13.4% drop. This suggests that, on some days, the ICR folks didn’t have the energy left to go burn some extra calories at the gym.

So what gives? I’m a fan of time-restricted intermittent fasting where there’s an eating ‘window’ of time each day, usually between 4 and 8 hours. This approach was not tested in this study. We’ll tackle that topic in a future post.

This article was originally published on FOODSCAPE finds

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