Does Intermittent Fasting Work?

Intermittent fasting is one of the hottest new diet trends. Proponents say it can help you lose weight, improve blood sugar metabolism, and slow aging. What's the research on this new fad?

Monica Reinagel, MS, LD/N, CNS
4-minute read
Episode #500

Unfortunately, the human studies haven’t been quite so dramatic. Intermittent fasting and restricted eating windows tend to lead to weight lossbut that's because people following these regimens end up eating less. These approaches also can lead to improvements in body composition, cholesterol, and blood sugar metabolism but no more so than in people who lose weight through more traditional dietary approaches.

Although we keep hoping to discover a magic formula that allows us to lose weight without actually eating less, we haven’t found it yet. It still does come down to taking in fewer calories than you use. But there are a lot of approaches that result in reduced calorie intake. You can decide to avoid certain foods. You can eat everything but in smaller portions. You can fast once or twice a week and not think about it the rest of the time. You can institute a restricted eating window.

Is Intermittent Fasting a Better Way to Lose Weight?

All of these approaches have pros and cons and we can talk about how each can be optimized. But when it comes to which is best for losing weight and all the health benefits that flow from that, it really boils down to which one is the most sustainable for you. What suits your lifestyle personality and preferences? Because when it comes to weight loss, your ability to maintain a lower weight long-term trumps just about every other consideration.

But what if you don’t need to lose weight? Does intermittent fasting have anything to offer? A couple of studies have tried to tease apart the effects of meal timing from the effects of weight loss by doing studies where people ate just once a day but still ate enough to maintain their weight.

In particular, researchers were interested to test the hypothesis that eating the same amount of food but in a shorter time period would help improve blood sugar metabolism. Results so far have been mixed but if your goal is improve your glucose metabolism, early results favor putting your restricted eating window in the first half of the day and not the second—which most people find to be considerably less appealing.

The Bottom Line on Intermittent Fasting

We need to do a lot more research into the long-term effects of intermittent fasting on health and to sort out which of the various approaches produce the best results and for which people. There are a few groups for whom intermittent fasting may not be appropriate, including pregnant women and people with a history of eating disorders. Anyone using medications to manage their blood sugar should seek guidance from a nutrition or health professional before experimenting with any sort of fasting protocol.

But if you are not in any of those categories, you need to lose weight, then this might be something that can work for you. Despite the popularity of the 5:2 Diet, which is an alternate day fasting protocol, I am a little more drawn to the restricted eating windowin part because people seem to find it more comfortable and easier to sustain. If you decide to experimentor you have been experimenting with it alreadyI’d love to hear how it’s working for you, what you like about it, and how long you’ve been doing it! You can post your thoughts below or on the Nutrition Diva Facebook page.

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About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.