If you can survive the hunger pangs, it sounds like a pretty good deal: Eat less than a supermodel and, in turn, tack a few decades onto your life. Research has shown that ultra-low-calorie diets can improve the longevity of other animals, so why not humans too?

While you may have heard the hype about extreme "calorie restriction" ‑- cutting your food intake by 30 or 40 percent indefinitely ‑- some experts say it's a bad idea.

"In a nutshell, don't do it," advises Lona Sandon, a spokeswoman for the American Dietetic Association. "You need to be sensible about how you approach weight loss, and starvation is not a sensible approach."

To be fair, the aim of calorie restriction (CR) is not starvation. Calorie-restricted diets for longevity are about obtaining the maximum amount of nutrition in the smallest amount of calories by eating only nutrient-dense foods. What does this diet look like? No simple sugars or carbohydrates; plenty of vegetables, especially green, leafy ones; and protein from sources with little to no saturated fats. As you might have guessed, people who subscribe to these diets end up losing a significant amount of weight, at times looking almost emaciated. This begs the question, is a skeletal physique the image of vitality and long-lasting youth?

Perhaps not. This past April, the government released a report suggesting that slightly overweight people live longer than not only underweight people, but those of normal weight as well. This was good news for those of us who were never going to see a size four again ‑- as if we ever had in the first place. The study from the U.S. Centers for Disease Control and Prevention (CDC), published in the prestigious Journal of the American Medical Association, made many Americans rejoice, and many scientists scratch their heads.