Intermittent fasting: dispelling the BS (bad science)

What do Miranda Kerr, Ben Affleck and Christie Turlington have in common?  Apart from being really, really ridiculously good looking, that link is intermittent fasting. Yes intermittent fasting is the new black and if you ain’t intermittent fasting, well you ain’t…….

A simple Google search on intermittent fasting finds it to be overwhelmingly positive – curing your cancer and making you saucily slim at the same time. You ripper! Unfortunately that’s probably since you’re coming across the websites of spruikers with an interest in intermittent fasting related products, or those without a health research background, who seem to promote anything slightly absurd and sexy. So, is intermittent fasting all it’s cracked up to be? Or is it just another crock?

What is intermittent fasting?

Before science gives you its definitive answer, what exactly is intermittent fasting? Broadly speaking, intermittent fasting refers to any dietary regimen where you stop eating or limit your calories for a defined period of time before returning to eating. There are various different timing ratios, but the most popular is the 5:2 pattern, where you eat normally for five days and for two days restrict your daily caloric intake to only 500-600 calories. Because you’re not really changing what you’re eating, but simply the timing, the diet’s proponents say it isn’t actually diet.  But does this mean it works?

Why it might work?

There are several theories as to why intermittent fasting might work. A major one is that having small breaks from eating will lead to less eating overall – because you’re not eating during fasting and when you return to eating your stomach is smaller and you have less of an appetite.

Another proposed mechanism is that when you’re not eating, you’re not putting glucose into the bloodstream. This then means you don’t produce insulin in response to clear that glucose. Insulin causes you to preferentially burn glucose over fat. Therefore, if you fast you should, in theory, be burning fat instead of sugar, causing you to be less fat, more skinny and objectively more handsome/saucy/sexy. Hallelujah!

Does it actually work?

Theory is all good and well, but if this theory doesn’t translate to actual health improvements in humans then it don’t mean jack, Jack. Well, here we go then.

A review of various human based studies on time restricted feeding, a component of most intermittent fasting eating regimes, found it to lead to: weight loss, decreased LDL (bad) cholesterol, triglycerides and increased HDL (good) cholesterol in most, but not all cases (1).  Looking fairly promising thus far.

Another review study, compared the benefits of intermittent fasting to standard caloric restriction: decreasing how many calories you eat. Standard caloric restriction was more effective than intermittent fasting for weight loss. But both equally decreased insulin resistance and visceral fat (2), which could prevent diabetes and various other chronic diseases. So if caloric restriction may be very slightly more beneficial than intermittent fasting, then why don’t you just eat less? Well, read on, my wayward son.

Why don’t you just eat less?

Yes, a major theory as to why intermittent fasting may work, is that you actually consume fewer calories. There is minimal to no scientific evidence surrounding this topic, but intermittent fasting may lead to an overall reduction in caloric intake and it may be easier to adhere to intermittent fasting than an overall low calorie diet in uncontrolled, non-scientific circumstances. It’s your classic occasional Ben and Jerry’s versus no Ben and Jerry’s type scenario!

Are there any negatives to intermittent fasting?

Before we provide our verdict, are there any negatives to intermittent fasting?  So many questions!

A common concern surrounding intermittent fasting is that it will make you feel terrible and impair your: cognitive function, athletic performance and even sleep.  Well, we can’t deny that it might make you feel lacklustre, especially initially.  However, there is good evidence that intermittent fasting does not effect, or very modestly negatively effects athletic performance. Suggesting you would have to be a very high level athlete for it to impair your performance (3). As for sleep, it doesn’t appear to substantially negatively effect sleep (4) and finally, in terms of cognitive function, it may actually make you a little bit sharper. This is since the lack of food is said to stimulate hunter gatherer instincts and in turn raise cognition (5).

However, before you go out and stop eating, fasting regimens have not been tested in: diabetics, children, the very old and underweight individuals, and it is possible that this dietary routine may be harmful to these populations. If that describes you, maybe give it a miss for the time being.

Is it healthful?

Current scientific evidence is limited, however, intermittent fasting looks to be beneficial for metabolic health and weight loss, with no significant substantiated negative effects reported in the scientific literature yet.  If you’re already healthy and have no problem restricting your calories, then based on current data it’s unclear if intermittent fasting will be of benefit to you. In contrast, if you struggle with metabolic health, weight loss and limiting calories, then intermittent fasting may be a good strategy.

Finally, whether you’re fasting or not, there is no replacement for good diet and you should try to eat healthy, nutritious foods.

Our verdict: moderately healthful. 

We’d love to hear your opinion on intermittent fasting, please comment below.

I hope this has been healthful!