If you've ever gone to sleep hungry and then dreamed of chocolate croissants, the idea of fasting may seem completely unappealing.
But what if the payoff for a 16-hour fast — which might involve skipping dinner, save a bowl of broth — is a boost in energy and a decreased appetite?
This is what we've experienced as we've tried out the so-called 5:2 diet. It's an intermittent fasting approach that, as we've reported, has been popularized by books by British physician and television broadcaster Michael Mosley. The diet calls for two days per week of minifasting where the aim is to go a long stretch, say 14 to 18 hours, without eating. During these two fasting days, you also eat only about 600 calories, give or take.
It sounds tough. But here's the easy part: The other five days of the week you forget about dieting and return to your normal pattern of eating.
It's not really weight loss we're interested in (though, admittedly, we ate and drank too much over the holidays).
The fascination is what researchers say may be the broader benefits. Scientists are looking into how fasting may help control blood sugar, improve memory and energy and perhaps boost immunity.
A study by researchers at the University of Manchester found that when overweight women followed a 5:2 approach, they lost more weight and body fat and improved their insulin resistance compared with women who followed a more traditional diet of limiting calories seven days per week.
One explanation for the success of the 5-2 dieters could be that a day of minifasting can lead to a diminished appetite. As Allison reports on All Things Considered, she found that she's just less hungry the day after a fast.
Mark Mattson, a researcher at the National Institute of Aging, says when we go without food, the body uses up its stored glucose, the basic fuel for the body, and starts burning fat.
Mattson is interested in what happens to the brain — in terms of memory and learning — when the body starts to burn fat for fuel. And he's been studying animals, mainly mice, for clues.
During fasting, he says, fat can convert to compounds called ketones, "which have beneficial effects in making neurons more resistant to injury and disease." He's planning a study in people to evaluate what effect intermittent fasting may have on brain health.
And, as Eliza has reported, scientists are also studying how intermittent fasting may help boost immunity, perhaps by making cells more adaptive to stresses such as injury and disease.
There may be an evolutionary explanation for this because humans (and other animals) have fasted intermittently for much of our time on Earth, after all. As a recent paper in the Proceedings of the National Academy of Sciences notes, "The most common eating pattern in modern societies, three meals plus snacks every day, is abnormal from an evolutionary perspective."
Of course, doctors don't recommend minifasts for everyone. Valter Longo, a gerontologist at the University of Southern California who studies fasting, notes that "it is very dangerous for people who struggle with eating disorders to fast." And he advises everyone interested in fasting to see their physician and meet with a registered dietitian.
Longo and other experts gave Eliza some of their other tips on how to do it right:
- Fasting is easier with a buddy.
- On a minifast, choose the food you do eat carefully. Researchers recommend high-protein, high-fiber foods. Avoid refined carbs and sugar, which will spike blood sugar and may leave you hungry late in the day.
- To minimize temptation, stay out of the kitchen and away from food establishments.
- Try a pattern of weekly intermittent fasting for at least a month. Studies have shown that a long-term lifestyle change (and the benefits associated with it) is more likely for people who can stick with the diet for at least a month. And tolerating some hunger gets easier the longer you do it.
- Don't be surprised if there are some side effects, like trouble sleeping or gastrointestinal issues.
MELISSA BLOCK, HOST:
If your New Year's resolutions to eat better, be healthier and shed a few pounds haven't quite panned out yet, here's a strategy you may not have considered, intermittent fasting. NPR's Allison Aubrey is here to talk about an approach that's gaining a lot of traction among dieters and researchers who are studying the possible benefits beyond just weight loss. And Allison, intermittent fasting gives us a sense of what it is - fasting every now and then?
ALLISON AUBREY, BYLINE: Right. Well, the idea here is not to starve yourself for days. I like to think of this more as a mini-fast where you go, say, a 14 to 18 hour stretch without eating one or two days a week. The most well-known plan out there is called the 5-2 diet, popularized by a British physician. And this is where you eat normally for five days out of the week and then you pick two days a week when you do a mini-fast. So for example, you have an early dinner around 5 p.m., and you don't eat again until breakfast the next day at 8. That means you've done a 15-hour mini-fast. And the aim is that on these two days, you cut way back on the number of calories that you're eating to just 500 or 600 calories a day.
BLOCK: That's the catch.
AUBREY: That's right. That's the catch.
BLOCK: And Allison, you've been trying this intermittent fasting. You have a lean and hungry look to me. How's it going?
AUBREY: (Laughter). Well, you know, since this has been generating so much interest among scientists over in the U.K. and here, I decided hey, why not? I'll try it - not so much for weight loss but for other possible benefits such as lowering blood sugar and increasing energy and focus. That sounds good, right?
BLOCK: Yeah, sure.
AUBREY: And I have to say, it is challenging. I won't eat anything after 5 o'clock. So that means I'm at home cooking for my children, not eating dinner, and don't eat again until the next morning. So it can be challenging when you get started.
BLOCK: Yeah, 600 calories doesn't give you a lot of flexibility. What are you trying to eat on those days?
AUBREY: Right, well, you know, you can eat what you like. But be realistic. If you're down to 500 calories, these calories have got to hold you. So you're basically eating a lot of lean protein, greens, other non-starchy vegetables. And the important part here is to go that long stretch of at least 15 hours without eating.
BLOCK: Any downsides, Allison, besides crankiness, as I imagine...
BLOCK: People for whom intermittent fasting is a really bad idea maybe?
AUBREY: So I think that there are any number of people who probably wouldn't want to try it - pregnant women, children. If this is something that you're interested in and you have hesitations, certainly talk to your doctor.
BLOCK: Why do this though, Allison? Why not just reduce intake throughout the week?
AUBREY: Well, you know, this is where the science really gets interesting. Researchers at the University of Manchester in the U.K. tested this diet approach in about a hundred women. Half of the women in the group went on this 5-2 diet. The other half followed a more traditional, low-fat diet where they tried to restrict calories seven days a week. And what the researchers found is that the 5-2 dieters lost more weight. They lost more body fat compared to the women on the traditional low-fat diet. So this was a surprise. And what's more, the women on the 5-2 diet also saw improvements to blood sugar. So the researchers are still trying to untangle why this seems to be the more effective dieting strategy. But one thing I can say from my own experience is that these mini-fasts really seem to cut the appetite - or at least my appetite. One of the first days I tried this, I was really hungry when I was going to sleep. And I literally fell asleep, like, dreaming of a chocolate croissant. I was even planning my trip over to Union Station in the morning to buy my chocolate croissant. But when I woke up, I did not even want it. I think I had oatmeal instead. And I left half of the oatmeal in the bowl uneaten. So scientists say this pattern of eating may help regulate appetite so we don't eat as much.
BLOCK: Well, apart from appetite, Allison, you said you were interested in the effects of fasting on energy and on focus. What's known about how intermittent fasting might affect those?
AUBREY: Sure. Well, one of the scientists that I've been talking to is Mark Mattson at the National Institute on Aging. And he says fasting brings a lot of changes in body and brain chemistry. His studies in animals, mainly mice, find that going without food can change the way the brain gets energy. So he's studying how this affects learning and memory. And he's actually planning a study in people later this year. Researchers are also interested in immunity. It turns out that fasting seems to put a mild stress on the cells in the body. And again, studies in animals suggest that the cells become more resilient and better able to protect against damage and disease. So as Mattson likes to point out, you know, this eating three square meals a day plus a few snacks - as is so typical of modern life - is very abnormal from an evolutionary perspective. Humans have, in fact, fasted intermittently for most of history, and perhaps there's a benefit to this.
BLOCK: NPR food and health correspondent and intermittent faster, Allison Aubrey, thanks so much.
AUBREY: Thanks, Melissa. Transcript provided by NPR, Copyright NPR.