The nutrition world was rocked last week by the publication of a new study, which concluded that intermittent fasting (IF) is not very effective for weight loss. What’s worse, the results suggest that it may exacerbate the loss of lean muscle tissue.
Intermittent fasting has been a topic of intense public fascination for several years now. I give workshops, lectures, and interviews on a wide variety of nutrition topics, to a lot of different kinds of audiences: physicians, nutrition and fitness professionals, senior citizens, college students, parents, and the popular media. And no matter what I’m talking about or who I’m talking to, as soon as we open up the floor or the phone lines, we inevitably get questions about intermittent fasting. Is it effective? Is it safe? What does the research say?
Is intermittent fasting effective? Is it safe? What does the research say?
So it was not surprising that this study caused such a splash. Despite the breathless headlines, though, the study didn’t actually change what we already knew about intermittent fasting and weight loss. And the new finding on muscle loss confirmed a suspicion or concern that many had already raised.
Why is intermittent fasting so popular?
The allure of intermittent fasting is understandable. The premise is that we don’t actually have to change what we eat or even how much we eat. We can lose weight simply by changing when we eat it.
There are a few different ways that IF can be practiced. One of the most popular protocols (and the one used in this latest study) is a restricted eating window. Instead of spreading your daily meals over the course of 12 or 14 hours, you shorten that eating window to 8 or 10 hours. For example, instead of eating breakfast at 7 a.m., lunch at 1 p.m., and dinner at 7 p.m., you might eat all your meals between the hours of noon and 8 p.m.
When researchers tried intermittent fasting in rats, it worked like gangbusters.
When they tried this in rats, it worked like gangbusters. Researchers gave the rats a high-fat diet and let them eat as much as they wanted. Not surprisingly, this led the rats to gain weight. But when they gave them the same diet and let them eat as much as the wanted for only 8 hours a day, they didn’t gain weight. In fact, the rats that started out overweight actually lost weight.
It seemed that the extended fasting period did something to the rats’ metabolism or hormones that caused them to either burn more calories or store less fat. If the same were true for humans, it would mean that, as long as we kept our mouths shut for 12 to 16 hours a day, we could eat all the pizza, cheeseburgers, French fries, and ice cream we...
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