Lose weight eating whatever you want?

Lose weight eating whatever you want? That’s the bold claim made by The Fast Diet, the new bestselling book by UK-based authors Michael Moseley, M.D., and Mimi Spencer, who say for five days a week you can pretty much go for it, milkshake AND fries included. And lose approximately 1–3 pounds per week.

The only catch? You have to fast two days a week.

More specifically, on two non-consecutive days, you must reduce the number of calories you normally enjoy by 25 percent. That’s approximately 500 calories a day for women, and 600 calories for men.

While the weight-loss claims may sound impossible, the diet, which is also known as “5:2” or alternate day fasting (“ADF”), is actually gaining credibility with some researchers and medical professionals, and several new studies suggest it works.

Still find the 5-day gorgefest and 2-day starvation protocol a little hard to swallow?

According to triple-certified nutritionist Dana James, the science checks out (though she’s quick to point out it’s not for everyone): “When you restrict your calories, the body activates its survival mechanisms,” turning up genes responsible for fat burning and switching off those responsible for fat storage. “Both of these changes will activate fat loss. However, it must be done on an intermittent basis, otherwise, you are turning on too much of a stress response within the body, and other cellular mechanisms will come into play to stop the fat loss,” she says.

Research also shows additional positive side effects of fasting, such as delayed aging and improved cognitive function. And who doesn’t want those?

Holes in the Science—and the Logic

But before you move your dinner plans to coincide with your new dietary regimen, there are still a few holes scientists have yet to fill in. Namely, the two-day per week rule is more of an educated guess, and the bulk of research so far has been done on animals.

Not to mention that the diet has been accused of reinforcing a binge-purge mentality. “Anyone with disordered eating—they know who they are—may take two days of fasting to mean an entire month of fasting,” says James.

James also doesn’t recommend heading to McDonald’s on your off-days, or blowing your 500-calorie allowance on a cheeseburger. To that end, Mimi Spencer and Sarah Shenker, an R.D. who has a PhD in nutrition, recently came out with The Fast Diet Cookbook, which features 100-plus nutritious (but admittedly skimpy) recipes that all adhere to the 500-calorie daily maximum.

In terms of how it will practically fit into your busy lifestyle, the Fast Diet gets mixed reviews. Some find the relatively short timeline easy to stick to, while others find that cramming into professional calendars can be a challenge. “It’s very doable, though it was difficult with work dinners—I can’t be the only one at the table not eating!” says Sabrina Chu, a trader at a financial firm.

Nowadays, “I can’t meet for dinner, I’m on a cleanse” is a common and accepted excuse. No word yet on whether the same will become true of intermittent fasting. —Carla Vass

For more information, visit www.thefastdiet.co.uk