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? Read the transcript at https://www.quickanddirtytips.com/health-fitness/weight-loss/does-intermittent-fasting-work Check out all the Quick and Dirty Tips shows: www.quickanddirtytips.com/podcasts FOLLOW NUTRITION DIVA Facebook: https://www.facebook.com/QDTNutrition/ Twitter: https://twitter.com/NutritionDiva
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?
Read the transcript at https://www.quickanddirtytips.com/health-fitness/weight-loss/does-intermittent-fasting-work
Check out all the Quick and Dirty Tips shows:
www.quickanddirtytips.com/podcasts
FOLLOW NUTRITION DIVA
Facebook: https://www.facebook.com/QDTNutrition/
Twitter: https://twitter.com/NutritionDiva
One of the biggest diet and nutrition trends these days is intermittent fasting. Every week, I hear from listeners wanting to know my thoughts on it. I've mentioned intermittent fasting on the podcast before, in an episode on the health benefits of fasting. But that was way back in 2011. At that point, the research was still quite preliminary and most of it had been done in rodents. Nonetheless, researchers were excited about the potential for intermittent fasting to prevent or reverse diabetes, weight gain, DNA damage, and other artifacts of aging.
Based on these promising but preliminary results, lots of people started experimenting with various forms of modified or intermittent fasting—generating a lot of positive anecdotal reports. Over the last few years, more studies have been done—some of them on actual humans.
Before I dip into the latest research, let me define some terms. Intermittent fasting is an umbrella term that includes a pretty wide variety of approaches, most of which fall into one of two categories: alternate day fasting and restricted eating windows.
Alternate day fasting involves switching back and forth between days when you eat more and days when you eat less. In some versions, you eat nothing or next to nothing on your fast days and as much as you want on your feast days. Other versions have you cut your usual food intake by a third to a half on your fast days and allow you to eat more than your usual food intake on your feast days. (This is sometimes described as calorie cycling.)
The proportion of fast to feast days also varies. Some protocols have you fasting every other day. Another popular variation is the 5:2 diet, where you fast for two non-consecutive days every week.
The other approach that’s commonly included in discussions of intermittent fasting is the restricted eating window. I talked about this in my episode on timing your meals. Instead of restricting your food intake, you restrict your meal schedule.
Again, there are lots of variations on this approach. Some people follow a four-hour eating window, essentially eating just one meal a day. Others might eat two or three meals within an eight or ten hour window. (If you’re a breakfast skipper, you might already be doing this without even realizing it!)
The timing of the window is also up for debate. Because of our circadian rhythms, it might work better to put your eating window in the first half of the day. But due to our social rhythms, most people who follow this approach prefer to have their eating window in the second half of the day.
A lot of the current excitement about intermittent fasting is still based on some of those early animal studies, which found that intermittent fasting led to weight loss, improvements in body composition, blood sugar metabolism, and other exciting things—even though the rats were eating the same amount of food!
Unfortunately, the human studies haven’t been quite so dramatic. Intermittent fasting and restricted eating windows tend to lead to weight loss—but 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.
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.
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 window—in part because people seem to find it more comfortable and easier to sustain. If you decide to experiment—or you have been experimenting with it already—I’d love to hear how it’s working for you, what you like about it, and how long you’ve been doing it!