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Making Sense of the 5 and 2 Diet

Periodic fasting is not new. During the month-long Ramadan, for example, Muslim people fast from sunrise to sunset. As a weight-loss regime though, intermittent fasting has only started to be investigated quite recently. There have been a few decent quality studies looking at the effectiveness of alternate day fasts (one day eating normally, one eating 25% of your usual calories), and intermittent fasting (2 non-consecutive days eating 25% of your usual calories) on weight loss. They also looked at the effect of fasting on things like cholesterol, and blood sugar control in type 2 diabetics.

Does it Work?

Both alternate-day and 5:2 fasting lead to weight loss. Not at all surprising, given that people are eating less calories each week! In a recent study comparing the 5:2 regime to regular daily calorie restriction (ie, both groups eating the same amount of calories over the week), there were a few small extra benefits from the 5:2 regime. Both groups lost around 600g per week, but 34% of the 5:2 group lost more than 10% of their weight at 6 months, compared to 22% in the regular group. The 5:2 group had slightly greater improvements in insulin sensitivity than the regular group. And, at the 6 month mark, 64% of the 5:2 group were sticking with the diet, compared with 55% of the regular group.

Great. Are There Any Downsides?

The main downside is that contrary to popular opinion- those 5 days of ‘regular eating’ do not mean ‘eat anything’! The 5 non-fasting days do still need to be calorie controlled. You still need to have eaten less calories than your body has used over the whole week before you’ll see any weight loss. Think about your typical weekends, do you go out for meals and eat rich foods or drink alcohol? Overdo it too much and you’ve just eaten that calorie deficit you starved for during your two fasting days! Your weight might stay stable doing this, but it probably won’t go down unless the other 5 days are on track.

Intermittent fasting could also promote disordered eating, or bingeing in susceptible people. Or, it could mask an eating disorder to friends and family. But the main issue is whether your client could see a plan like this fitting their lifestyle. For this reason, the first question I ask my patients is always, “Can you see yourself continuing to eat that way a year from now?” If the answer’s no, it means that, regardless of evidence for or against the regime, it’s a fad diet for them. In that case, they’re far better off deciding on one small change that they can implement now, and stick with every day. It’s un-sexy advice, but small changes over time really do add up!

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