My quarantine 15 (or 20, actually) went in the opposite direction. Yep, somehow during lockdown I managed to lose weight instead of gain it. How on earth did that happen? I stumbled into intermittent fasting.

This eating pattern has gained traction in the last few years, but it never grabbed my attention because, frankly, it sounded awful. Skip meals — what? Why would I ever want to do that?

Well, a growing body of research suggests the benefits of intermittent fasting are numerous. It turned out to be the easiest way I’ve ever lost weight.

It didn’t start on purpose. I found myself without an appetite from worry in the early days of the pandemic, so I’d skip breakfast and sometimes lunch, then eat when I got hungry again.

Sound unhealthy? When I spoke with Mark Mattson, Ph.D., a neuroscientist at Johns Hopkins University School of Medicine in Baltimore, an expert on intermittent fasting and co-author of a recent New England Journal of Medicine article on its benefits, he explained that it’s actually only relatively recently that humans began eating three meals a day. Prior to the agricultural revolution, he explained, humans couldn’t store food in the way we do now that enables us to graze and snack 24/7.

I rarely weigh myself, so I didn’t realize what was happening until my pants grew looser. Intrigued, I started looking more into intermittent fasting, as it’s sometimes called, and fell down the rabbit hole. Since it had seemed so easy, I decided to continue it with purpose, choosing to fast from dinner until anytime between noon and dinnertime again the next day, depending on how I felt. (Another approach to fasting involves eating normally five days a week and limiting calories to about 500 on two non-consecutive days.)

In the space of a couple of months I’d lost about 15 pounds (based on the last time I’d been weighed at the doctor’s office) with my intermittent fasting plan. I dialed back the number of long fasting days, but continued to skip breakfast, and another five pounds eventually came off, bringing me down two clothing sizes to the size I’ve been most of my life — when I haven’t let weight creep up on me like I had in the year leading up to this, that is.

I kept wondering why I never knew how easy this could be. Was I hungry? Sure. But not hangry, and that I could handle. I’ve tried — and hated — calorie counting in the past. This was dead simple; when it was time to eat I ate until I was full, mostly avoiding empty white flour carbs and processed food. If I got too hungry, I skipped fasting. It grew easier with time, which is typical, Mattson said. If people are going to adapt, it takes about a month to adjust.

Why was this so wildly effective? And is intermittent fasting healthy? It boils down to several factors.

Even though weight loss isn’t as simple as calories in, calories out, Samantha Cassetty, a registered dietitian based in New York City, said that just by virtue of only eating once a day on fasting days, I was still consuming fewer calories. Those meals, especially the first few months, were also almost exclusively prepared at home, away from restaurants where she noted portions are bigger, and there’s just no way to know how much fat and sugar is in a dish.

But unlike a more typical diet of reducing calories at each meal, I was also changing my eating pattern, reducing the size of the window when I’d eat.

Through this change, something more than simple calorie math is going on. When we eat, the energy from the food is stored in our livers in the form of glucose, Mattson explained. The liver holds about 700 calories of that glucose, and with normal daily activity, will burn through about 70 calories an hour.

That means if we are eating every few hours and snacking between meals, we never burn through all of it. Fast for longer than 10 to 12 hours, though, Mattson said, and the body switches from burning glucose to burning fat. That’s the magic moment, as I understand it. The fat cells go into the liver where they’re converted to ketones. That switch, Mattson said, from glucose to ketones, is what will allow people and animals to survive for days or longer without food.

“As far as weight loss it’s pretty simple,” he said. “If people are overweight that excess weight is fat, and if they do intermittent fasting, then they will use up fat during the fasting period. As long as they don’t overeat … they’ll lose weight.”

Intermittent fasting shows other benefits as well. The most intriguing to me was that the mild stress it places on cells is analogous to the stress exercise puts on muscle cells, Mattson said. “And having been subjected to that mild stress the cells change in ways that help them become stronger and resist more severe types of stress.”

It sounds like a no brainer. If you can handle being hungry a few hours a day, why not do it?

Well, it’s not for everyone. And there can be drawbacks. There’s a high dropout rate to this pattern of eating, Cassetty said. For some, prolonging a period of not eating “can make people feel very tortured, hungry and distracted, and it doesn’t promote productivity, energy, vitality and all those wonderful feelings,” she said.

There can also be missed social opportunities, such as dining with family and friends. And if you’re exercising, there’s a concern you may not be refueling your body adequately to repair broken down muscle tissue, she said. For older folks in particular, she added, it’s critical to replenish protein stores so the body can go into its maintenance and repair mode at night.

But if you’re a healthy person and want to give it a try, it’s OK to experiment, said Cassetty, however, she added, “if you have any health conditions you need to talk to a doctor before you do this.”

A 12-hour eating window is a good place for most people to start, Cassetty said, and if you want to take it a step further, try a 16-hour fasting window on a weekend when you might be sleeping through more of the fast. But Cassetty also emphasized that fasting isn’t an excuse to throw good nutrition out the window. It remains important to fill your plate with non-starchy vegetables, whole grains, lean protein and healthy fats.

And if it’s a success? Sorry, but there’s really no off switch. Maintaining the weight loss means continuing intermittent fasting. For me, at least, knowing that it’s relatively easy to do means that’s not a concern. Through this change I’ve set up some structure, essentially eliminating snacking. I’ve become much more in touch with my body’s signals, learning when I’m actually hungry and when I’m grabbing food just to have it. I don’t feel deprived because I know if I’m actually hungry I’ll eat, and I’ll eat well.