Intermittent fasting

Consuming only 600 calories on "fasting" days will require some careful measuring of portions. A 3-ounce grilled boneless, skinless chicken breast, which is about the size of a deck of cards, is 128 calories. (Mel Melcon / Los Angeles Times)

Will IF make you healthier?

A good deal of research suggests that IF may do your body more good than simply cutting it down a size or two. According to some studies, it may lower blood pressure, inflammation, triglycerides and bad cholesterol, as well as the risk of cancer. And it may speed up metabolism, fat burning and cellular replacement and repair. But results have not been consistent across studies, and in any case many of them have been done with rodents, so the results may or may not hold in humans.

Of the proposed benefits, many experts find IF's effects on improved insulin sensitivity most convincing so far.

Dr. Valter Longo, director of the Longevity Institute at USC, has studied fasting for years and believes it's a good step to take against many diseases of aging. "It's like taking your car to a mechanic," he says. "Your body gets a tune-up and then it can make a clean start."

But tuning up your body takes more time than a tune-up takes at the garage, Longo maintains, and more time than the fasting periods prescribed by most IF diets. "You need four or five days before your body gets a restart." So once or twice a year he does an extended semi-fast, allowing himself 600 to 800 calories a day for five days.

Not that Longo sees no use for IF. "A 5:2 diet is probably better than nothing," he says. And, as a weight-control measure, he's dedicated to his own version of an IF diet: skipping lunch most days, except, naturally, when he's visiting his mother in Italy.


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