Transcript for 20-Second Workout: Is 'Fast Exercise' the Best Thing for You?
In an age of instant gratification where we want everything fast, from fast food to fast fashion, we expect the same from our workouts. There was the seven-minute workout. Then the four-minute workout. But what if you could burn fat and be healthier even faster? Enter the 20-second workout. It may not the most dignified workout. It is burning. Burning if the groin. Reporter: But Michael mosley, a doctor turned best-selling author, says that just 20 seconds of grunting, groaning, and pushing your way through the pain, even in business attire -- Oh, my god. I can't -- that's 10. Halfway there. Whoo. Five, four, three, two, one. Reporter: Will make you not only skinnier but healthier. We're talking about high-intensity interval training. Pushing through to the absolute limit. Mosley calls it fast exercise. And it's the title of his new book. But can one minute total three times a week really lead to remarkable medical changes? The good doctor suggests it's an aerobic fountain of youth, a shortcut to getting maximum benefits with minimum work. What's the key to high intensity? This regime, doing short bursts of intense, seems to be much more effective not only for losing weight but also for improving your insulin sensitivity. Reporter: Mosley's controversial take points to a growing body of science which suggests it's the stress and intensity of exercise, not the duration that's beneficial. We're talking weight loss, reduced cancer risk, and something that hits close to home for Michael, diabetes. Two years ago I discovered I was diabetic. I was a bit overweight. That got me into fast diet but also got me into a fast exercise regime. And now I'm 20 pounds lighter and my blood sugars are completely Normal. I've gone from diabetic to Normal. Reporter: As a Guinea pig for his own research, he stays healthy now. But not with a fancy gym. Running is a fabulous form of exercise. You can do it in any building which has floors -- Why am I getting nervous? I'll give you a head start. Ready, steady, go. Running? It's another 20-second workout, one you can do right in your own stairwell, in a suit, whether you're fit or fat. That's it? That was intense. Also vaguely humiliating because you were so much faster than me. I'll come back in two weeks' time and I'll bet you beat me. Really you no longer have an excuse you don't have time to work out. Not at all. Reporter: The fast workout is just the latest trend from Dr. Mosley. His bbc documentary which aired on pbs "East fast and live longer" launched an international best-seller about the benefits of a two-day a week fast diet. It all began with a wake-up call for the good doctor about where his then 53-year-old body was heading. He'd already lost his father to diabetes. I discovered that my fasting glucose levels were those of a diabetic. My doctor said you need to start on medication. Reporter: Researchers across the United States have been finding astonishing results from severe calorie restriction. Decreased cancer risk, increased life expectancy, even improved brain function. So mosley came up with a diet where you fast on two random days of the week, say, Monday and Thursday, and eat whatever you want the remaining five. Just to be clear, you're not telling people to starve themselves. Oh, absolutely not. In the regime that I'm suggesting, the maximum you ever go without food is 12 hours. Reporter: Mosley believes he can apply the same principles from his diets to his workouts by looking carefully at the science to trick your body into being healthier. When I did the fast diet, the fasting, again, the benefits there come from stressing your body. It's a hunger thing. Right. And the same is true of exercise. Reporter: High intensity interval training, or hit, is nothing new in the exercise world. The wildly popular cross-fit phase. Daniel rohana incorporates high intensity routines for his clients at reebok. But rohana says high intensity should be balanced with other types of exercise. I do think high intensity's got its place, but I think, you know, a well-rounded program with much more scientific background is much more efficient. Reporter: But there are critics who say just a few minutes a week really won't cut it. Exercise should be varied and gradual. So high-intensity training should be a supplement to that. Reporter: And working out with this much intensity isn't easy for everyone. If you're a couch potato and you think oh, 20 seconds and I'm done -- If you don't exercise, don't try it. If I ran a sports medicine clinic, I might want you to if I need some new clients. Reporter: But it comes to working out the idea that less is more can be very tantalizing. Are we done yet?
This transcript has been automatically generated and may not be 100% accurate.