Everyone knows that guy -- the one who can chug more than his fair share of beer, scarf down an entire pepperoni pizza, grab an ice cream, and make a donut run the next morning, all without gaining a pound.
Meanwhile, others go easy with the dressing on their salad, stick to something light at happy hour, and maybe, maybe treat themselves to a few pieces of candy, hopeful that a cool 30 minutes on the treadmill will keep the scale in check.
What gives? Isn't everyone playing by the same rules of caloric intake?
Not exactly. A new study suggests that people's bodies respond to the same food in very different ways, which means that at least one measure of food's impact on metabolism -- the glycemic index, or how a food affects blood sugar -- isn't as reliable as once thought. And if the glycemic index is inaccurate, and foods don't elicit the same blood sugar response in everyone, it helps explain why so much nutrition advice doesn't hold up.
"If you have two people who are given the same exact diet, they won't necessarily weigh the same," says Dr. Judith Korner, director at the Weight Control Center at Columbia University Medical Center. "There is a genetic basis for how much they can consume."