Wednesday, September 13, 2017

Is intermittent fasting healthy?

The Study
Fasting or skipping meals has become a popular strategy for losing weight. However, the long-term health effects of this practice are not known. A recently published investigation in the American Journal of Clinical Nutrition looked into this question. In this crossover trial, 17 normal weight subjects underwent 3 separate 24-hour interventions: a day that they skipped breakfast, a day that they skipped dinner and a day that they ate three conventional meals.  Energy was measured in a respiration chamber and calories were kept constant on each of the three days. Blood glucose, insulin and inflammatory factors were measured throughout the study protocol. The results were quite interesting. Compared to 3 normal meals per day, when subjects skipped breakfast, they showed signs of disturbed glucose homeostasis and increased inflammation. American Journal of Clinical Nutrition 2017; 105:1351-61.

Take Home Message
This is the second recent publication that has shown a disturbed glucose homeostasis with meal skipping or fasting. Disturbed glucose homeostasis has the potential to increase risk of type 2 diabetes. The increased inflammation found in this investigation with breakfast skipping is also problematic as inflammation has been associated with many chronic diseases. 

I don’t recommend meal skipping or fasting as a weight loss strategy to my clients. Besides the negative health consequences outlined in this study and others, it has also been shown to slow down metabolism in a recent investigation. When metabolism slows down, the risk of weight gain increases because you are burning fewer calories each and every day. 

If weight loss is your goal, eat 3 nutritious meals each day. In addition, hit your cardio goals and lift weights at least twice per week. Be patient with your rate of weight loss, there are no quick fixes.

3 comments:

  1. not sure why my previous comment didn't post but I showed multiple studies that actually find very positive effects of intermittent fasting. I also pointed out that the study above has questionable methodology, an N of only 17. Here's another study that shows positive effects of IF in mice. I will try to post some other studies as well. https://www.ncbi.nlm.nih.gov/pubmed/28825965

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  2. https://www.ncbi.nlm.nih.gov/pubmed/27737674
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3946160/
    https://www.ncbi.nlm.nih.gov/pubmed/19423320
    Some more articles for your viewing pleasure!

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  3. Thanks for commenting on this post Elizabeth,
    I'd have to disagree with you on the methodology of this study. In my opinion, it is very well designed. Regarding sample size, it is reported in the manuscript that for 80% power, a sample size of 13 was needed. Therefore, 17 subjects provides more than adequate power for this investigation.

    I appreciate the links and took a quick look at them. While I find studies on rats very interesting, I generally don't use them to formulate my recommendations for people. In my experience, there have been too many instances where similar results are not found when replicated with human subjects. There have been very few studies on the short-term effects of intermittent fasting in humans and none that I can think of on the long term effects. While I have not done an exhaustive search in this area, I read the nutrition research monthly and have not come across many.

    The two that I reference in this post are among the first that I have seen in reputable journals. The fact that both have found a disturbed glucose homeostasis is troubling to me. You may lose weight with fasting but I can't endorse any weight loss strategy that has the potential to increase risk of disease.

    Either way, the jury is still out on this one and more research is needed. I'll keep looking for these types of studies and will post on them when I find them.

    Thanks again for commenting!

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