Photo: Studio D

There's your friend in the size 6 jeans who always seems to be attacking a cookie-dough ice cream cone; there's the stick-figure colleague who lunches on burritos the size of her head. And then there's you. Day after day, you toss the bread from your turkey sandwich, nibble on a Baggie of carrots, and refuse desserts—yet you can't get the scale to budge downward. How is it that you're still heavy when you'd swear on a stack of pancakes, "But I don't eat that much!" Of course, many will acknowledge there's no mystery as to why they struggle with their weight: They eat more than they should. But a persistent minority of people recount tales of heroic food deprivation followed by a humiliating inability to lose a single pound. What's going on with them?

Here are three possible explanations:

• Second-helping amnesia
• Stealth Spud Syndrome
• A Weight Vaccine?