Does science support intermittent fasting?

Ever heard of Intermittent Fasting? It’s a new(ish) trend in nutrition that seems to be getting enough traction that it may soon evolve from nutrition trend to nutrition approach. In a nutshell, intermittent fasting (IF) involves building periods of fasting into your life. How long and how often a person fasts is variable, although there are two approaches that seem to be the most common:

1. Fasting for a 24 hour period once per week.
2. Fasting between 10pm and 2pm every day.

The last time I reviewed the research, there seemed to be some evidence supporting intermittent fasting as a means to lose fat. In fact I wrote a blog post that outlined some of the benefits of intermittent fasting a few years ago. While it was not exhaustive, when combined with anecdotal observations and well-written postulating articles from respected professionals, it had me convinced that it was worth consideration.

I was in the process of suggesting it as an option recently when I realized I was not up to date on the research. I decided to do some reading. This journal article about the health implications of skipping breakfast piqued my interest as it points to skipping breakfast as a risk factor for cardiovascular disease, diabetes, and obesity. Here I was carrying the opinion that intermittent fasting is a potentially legitimate weight loss tool, while reading that it is a risk factor for obesity.

I’ll be honest that I read the article with scepticism. Sure enough, the authors do display some evidence of bias toward their thesis that skipping breakfast is unhealthy, but the bias is minor enough that I could get past it. I’m glad I could, as it appears this bias is not without evidence.

If you’re a nutrition geek, do yourself a favour and read the full paper. You’ll probably shake your head a couple of times, but I suspect you’ll agree it is comprehensive. Or at least it is in my opinion, but I acknowledge my understanding of nutrition may be inadequate to make that assessment. That said, I believe my background in engineering taught me to read and judge scientific papers effectively. If you are more versed in nutrition than I, and you disagree that it is a sound article, I’d love to hear from you.

For those who aren’t nutrition geeks but are interested in intermittent fasting, here are some notable findings:

  • Habitual breakfast-eaters who skipped breakfast lost more weight than those who continued to eat breakfast, while habitual breakfast skippers who consumed breakfast lost more weight than those who continued to skip breakfast. In other words, changing from one approach to the other yielded better results than either eating breakfast or not eating breakfast.

Possible take away: This makes me wonder if intermittent fasting is something that should be cycled?

  • A 12 week open lab trial involving 93 obese and overweight women with metabolic syndrome is described. Participants were put on a 1400 calorie a day diet, where one group consumed 700 calories for breakfast, 500 calories for lunch, and 200 calories for dinner; and the other group consumed 200 calories for breakfast, 500 calories for lunch, and 700 calories for dinner. “After 12 weeks, although body weight, waist circumference, fasting glucose, and insulin were reduced in both groups, they were all significantly lower in the breakfast group”.

Possible take away:Does this suggest that a 4pm to 8am fast would be more successful than a 10pm to 2pm fast?

  • A 4 week randomly controlled trial of 36 men and women with obesity were given either a high-fiber or a low fiber cereal for breakfast or they ate no breakfast. The no-breakfast group lost more weight than either breakfast group. Of interest here is that the no-breakfast participants had increases in good, bad, and total cholesterol.

Possible take away:So here is evidence that skipping breakfast was better than eating breakfast for weight loss. As for the cholesterol part, admittedly I’m a bit confused these days on the status of cholesterol with respect to health. “Old school” information tells us that we need to watch our cholesterol as high cholesterol (or specifically high bad cholesterol) is damaging to our heart health. Meanwhile some “modern” thinking suggests that cholesterol is irrelevant. Honestly I have no idea what to believe and so I’m just going to bury my head in the sand about it until either the science gets more clear or someone can convince me that the current science is more clear.

  • Studies were discussed about alternate day fasting, where participants either fast entirely every second day, or they consume a small amount of food. For alternate day fasting, “body weight decreased significantly in all studies by 3% to 8% after 3 to 24 weeks of treatment. Studies that provided food on the fast day produced the greatest weight loss.”

Possible take away:This also shows that skipping breakfast (and lunch and dinner) yields weight loss. Does it also suggest that intermittent fasting needs to be more aggressive to work? It seems the alternate day fasting studies have more convincing weight loss results than studies involving altered meal timing or single day fasts. It’s interesting that those who consumed some food on the fast day lost more weight than those who didn’t. Does that suggest it’s not just calories-in-calories-out? Or did those who ate a small amount on their fast day eat less on their feeding day? The participants ate “ad libitum” on the feeding day, meaning they ate what they wanted on the feeding day. The study did not publish how many calories they consumed, nor did it publish energy expenditure. So it is possible that this is still a calories-in-calories-out scenario and that the participants who consumed a small amount on the fasting day either ate less on feeding days or moved more in general. Without knowing these facts, we can’t be sure, but we can point to it with interest.

So what’s the conclusion? Is intermittent fasting healthy or not?

I hate to say it, but the answer is probably still I don’t know, although I would now argue that the evidence against intermittent fasting is a bit stronger than the evidence for it, with the possible exception of alternate day fasting.

There is one aspect of health covered in this paper that I largely glossed over: insulin resistance. The paper does discuss the effect of intermittent fasting on insulin resistance in many studies, and it appears clear that insulin resistance is reduced with intermittent fasting – often dramatically. Reading that after reading results of studies showing eating breakfast was more favourable for weight loss than skipping breakfast gave me a real ‘what if’ moment.

Is it possible that the reason so many blog posts support intermittent fasting for weight loss is that the authors extrapolated insulin resistance to weight loss? That would be interesting. And, it would seem, wrong.

Science is tricky sometimes, and this is one of those times. Science may or may not provide the answer; sometimes all it does is provide more questions. So how does one continue to provide science-based advice when the science is muddy? Just be open about how muddy it is.

Do you have an opinion on intermittent fasting? Or perhaps you’ve read and experienced enough that you can make a statement on intermittent fasting? Please share in the comments below. Just please be open about muddiness if your are sharing opinions or small sample experiences.

 

Elsbeth Vaino, B.Sc., is a personal trainer in Ottawa who enjoys reading science, but gets annoyed by opinions and theories presented as science.

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4 thoughts on “Does science support intermittent fasting?”

  1. Thanks for sharing, Shanta. I guess I’ll throw your question back at you – so how much of a fast is positive versus negative? When you skip lunch, how long do you go without eating? How is it that fasting for say 8 hours (sleep or breakfast to dinner) is good for digestion but fasting for 12 hours (not eating from dinner to lunch) will suddenly invoke a starvation effect? It seems unlikely to me that there would be a step-function like that. Of course I don’t know the answer but I think if we ask questions like this, we see that maybe our ideas about when we should or shouldn’t eat are not founded in history more than biology/physiology.

  2. Ya, lots of people have opinions about it, but so far the science is all over the map. Only one of the links above pointed to a scientific study and it was to a lit review of restricted time feeding in mice. From the studies I’ve read so far, it seems that intermittent fasting/time restricted feeding is more successful in mice than humans. Or I should say more conclusively succesful. The good news is that it’s getting studied more, so the body of evidence will hopefully start to become conclusive. Or what I think is more likely – scientists will get a better understanding of why, when, and for whom it will be successful.

  3. Hey Elsbeth,
    I asked my nutritionist about it. He thinks fasting has its place and it will help with fat loss if you learn how to do it properly and there is a lot of research to support its effectiveness. But he personally does not think it as a fat loss tool. Here is a link he suggested to learn more about it:

    https://tim.blog/2015/11/03/dominic-dagostino/

    https://www.ketogenicforums.com/t/joe-rogan-and-dr-rhonda-patrick-talk-about-if-and-restricted-time-eating/5786

    https://www.youtube.com/watch?v=-R-eqJDQ2nU

  4. I know that when I skip a lunch once or twice a week I feel less bloated especially if I am taking (consistently) a probiotic. Kind of gives my digestive system a chance to catch up. Important thing is, to drink plenty of water. I am not a supporter of skipping breakfast…how could fasting your body all night and then again until lunch provide the energy to function at home or work? Wouldn’t your body go into starvation mode? Just my 2 cents :)

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