Thin people watch portion sizes.

No, most thin individuals don’t travel with a food scale and measuring cups or demand fat-gram counts from waiters.

But to keep an eye on what they eat without being obsessive, many focus on filling their plates with mostly fruits, vegetables, and lean protein. “No one ever got fat from a grilled shrimp,” says Stephen Gullo, Ph.D., a psychologist and the author of The Thin Commandments Diet (Rodale, $25, www.amazon.com).

They also use strategies such as buying just a single serving’s worth of food, eating portion-controlled frozen meals, passing up gargantuan-portion family-style restaurants, and using smaller-than-normal plates.

The National Weight Control Registry (NWCR), an ongoing study of how more than 5,000 people keep off the weight they’ve lost long-term, has found that successful weight maintainers tend to eat five small meals a day rather than three squares, which may make it easier to scale down portions.