Ramadan Mubarak! Does Fasting Really Work?

For the next 28 or 29 days, many Muslims will abstain from food and drink from sunrise to sunset. Coincidentally, this year’s Ramadan coincides with the period of Lent for Christians, which was traditionally a period of 40 days of fasting. Fasting is part of every religious tradition.

These days, many of us use fasting for health purposes. The way to fast that’s become the most popular is probably some kind of daily fast. Some people refer to this as “intermittent fasting”, but in the academic literature we tend to refer to this as TRE - time restricted eating. For me, anything more than 14 hours and less than 24 hours of fasting counts as TRE.

When we talk about fasting for health purposes, a fast is any period of time within which you are not consuming caloric foods. You can consume water or black tea or coffee. Other non caloric beverages (especially sweet beverages) may be a problem because they can fool your body into thinking that you’ve had sugar, thus triggering a spike in insulin levels, which is the main thing we’re trying to avoid when we’re fasting.

Fasting has become popular in some circles as a way to lose weight. But does it really work?

There have been some recent studies making headlines that cast doubt on the effectiveness of fasting. This study from the New England Journal of Medicine made headlines last year for supposedly showing that TRE doesn’t work. But that’s not really what the study found. As always, it’s worth reading the study itself (instead of just the headlines) to understand what’s going on.

This is a much better study than the one I previously analysed on erythritol. This study on TRE took 139 patients with obesity and randomly assigned them to one of two groups. The control group was a calorie restricted group, consuming at most 1800 calories per day for men and at most 1500 calories per day for women. The intervention group did the same thing, but they consumed all of their calories within an 8 hour window. So this is the 16:8 fasting protocol that many of you will probably be familiar with in addition to caloric restriction.

In 12 months, the control group had lost an average of 6.3 kilos or roughly 14 pounds, which, as anyone who’s ever dieted will tell you, is pretty good. The group that was doing intermittent fasting lost 8 kilos or about 17.5 pounds. So they did better. But the way the study was set up, they would have had to lose 40% more weight than the control group in order to reach statistical significance. Given that they were really only fasting on average 16% more than the control group (the members of whom maintained a fasting window more more than 13 hours without being told to do so), is it fair to expect them to do 40% better? The fact that they achieved about a 25% benefit in terms of weight loss seems impressive, even if not statistically significant.

And that's not all. Even if we concede that caloric restriction is the only thing that matters (though that's not what the study shows) TRE may be a powerful tool to help many people achieve caloric restriction. If you just try to eat less, you're likely to fail and you're likely to be walking around hungry all day. For reasons that I won't get into here, fasting is actually much easier than just eating less for most people. So TRE is a way to avoid many of the problems traditionally associated with dieting. 

Ramadan fasting can be seen as somewhat extreme because those fasting don't even consume water. But it's worth bearing in mind that until very recently, nearly all the data we had on fasting was done in Muslim populations who were doing Ramadan fasting. Those studies showed that this way of fasting was effective for weight loss and fat loss, though the effects tended to reverse themselves when participants went back to eating three meals a day. 

So what are the takeaways here? If you'd like to try fasting for weight loss but haven't as yet, do give it a go. Since it's always easier to do things with others, maybe join your Muslim friends on a fast or two. 

And if you are Muslim and planning to fast, try to think of ways to keep up the habit after Ramadan has ended. Fasting a couple of times a week or even just changing your eating times during the rest of the year can be a powerful tool in optimising your health.