Feast and Famine: Controversial 'Fast Diet' Weight Loss Plan Is Eat for 5 Days, Fast for 2 The latest diet craze instructs you to eat for five days and fast for two.

Feb. 28, 2013 -- The hottest British export might be boy band mania, from the Beatles to One Direction. And Americans are fascinated with Kate Middleton and her royal baby bump, but the next big British invasion, hitting stores in the United States this week, might be "The Fast Diet."

According to its creators, tons of Brits are losing tons of weight. But what's intriguing is that they're reportedly getting radically healthier by doing something that sounds truly unhealthy: Fasting.

Not every day, just two days a week. The other five days require zero willpower. Fast dieters can eat whatever they want, from cheeseburgers to croissants, in a guilt-free way, the backers of this diet claim.

On the Fast Diet, they're not actually starving themselves on the two fasting days, but close to it. They can consume just 25 percent of a normal adult daily food intake, which translates to a measly 500 calories for women and roughly 600 calories for men. Those calories can be consumed in one mid-day meal or spread out over the course of the day, but protein and lots of fruits and vegetables are highly recommended.

Tara McLaughlin said she lost 36 pounds over seven months on the Fast Diet, and she said her dress size isn't the only thing that has changed.

"On my normal days now my appetite has reduced, so even when I do try to over-eat I sometimes find it quite challenging," she said.

The British fasting craze is the brain child of Dr. Michael Mosley of London, who said people can mistake hunger for other symptoms, like boredom. He created the Fast Diet by fasting on two random days of the week, say Monday and Thursday, then he created low-calorie, nutrient dense recipes.

But Mosley says he never set out start a dieting craze. A doctor by training, his BBC documentary, "Eat, Fast and Live Longer," begins with a wake-up call from his doctor about where his 53-year-old body was headed.

"I had a bit of a nasty shock because I discovered that my fasting glucose levels were those of a diabetic," said Mosley, who lost his father to diabetes. "And my cholesterol levels [were] about twice [what] they should be."

He said his doctor told him he had to go on medication and if he stayed the course, he'd wind up like the average American in their 60's -- on eight to 10 different medications. So he embarked on a quest for the scientific fountain of youth and he found tantalizing clues in U.S. labs, where studies on fasting were being conducted.

Researchers across the country are finding astonishing results from severe calorie restriction, including decreased cancer risk, increased life expectancy and even improved brain function. Mosley said one scientist showed him research done in rats that showed brain cells could regenerate at a faster rate when the body was fasting, and they are about to start the research on humans.

By mimicking feast or famine conditions, Dr. Mark Mattson, a professor of neuroscience at John Hopkins University in Baltimore, discovered that the body and brain respond to each other in fascinating ways.

"What they found in rats is when they are deprived of food their brains start producing a protein called brain derived neuro-traffic factor," Mattson said. "What this does is it makes you feel happier and what it also appears to do is make you smarter."

Mosley tracked down a human trial of alternative day fasting led by Dr. Krista Varady at the University of Illinois. Varady compared two fasting groups: one eating high-fat food on their "feed days" and the other eating low-fat foods.

"Surprisingly we saw the same decreases in LDL cholesterol, that's the bad cholesterol, and in triglycerides, and also in blood pressure," Varady said in the BBC documentary. "In terms of cardiovascular diseases risk, it didn't matter if you were eating a high or low fat diet."

"Another big surprise," she continued, "was that after a day of fasting, people rarely gorge themselves on their feed days."

Instead of making up for all the lost calories, participants in the study ate just 10 percent more on feed days.

So when Mosley created the Fast Diet, he came up with a human diet plan to see if he could mimic the results he found in American labs. Over time, Mosley found that more than his waistline was changing.

"My taste buds have altered significantly," he said. "I actually tend to eat-- I still eat fish and chips…[but] It has had a dramatic effect on my body."

But there are nutrition experts who are concerned that it is too big a leap to go from "patient zero" to a runaway bestseller with derivative books also making waves. Keith Ayoob, an associate professor at Albert Einstein College of Medicine's department of pediatrics and child development, worries about nutritional deficiencies and the prospect of people taking the diet to the extreme.

"[The Fast Diet] is anecdotal, based on [Mosley's] experience, that's an opinion," Ayoob said. "I like to make recommendations that are based on good solid science and I'm not there yet."

But over the course of two months, Mosley said he lost nearly 20 pounds on his Fast Diet and his overall health improved.

"My body fat went down from 28 percent to 20 percent, and my blood glucose went down from diabetic to normal," he said. "My cholesterol went down from needing medication to normal."

"What I had was visceral fat, fat in the gut," he added. "So if you get rid of that then you also significantly reduce your risk of diabetes and heart disease."

Mosley said there is no evidence that fasting leads to eating disorders, but he warned pregnant women, anyone under the age of 20, under-weight people and those who suffer from eating disorders to steer clear of the Fast Diet.