Heavy habits

"There are success stories in dieting, and we have sufficient data from studies to show it begins with a high level of motivation," Eckel says.

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Rules don't fit all

It's clear, however, that applying strict rules to eating behavior doesn't work for most people, says Wansink, who was appointed in November as head of the Department of Agriculture's Center for Nutrition Policy & Research. The office is responsible for overseeing the "Dietary Guidelines for Americans" publication and other nutrition programs. But people can have success by making small changes. Demanding sweeping environmental changes is impractical and strict dieting is too overtaxing, he says.

"I think the answer lies somewhere in the middle," says Wansink, author of the 2006 book "Mindless Eating: Why We Eat More Than We Think." "We need to make small changes in our environment. That can be as small as moving fruits and vegetables to the middle shelf in the refrigerator. You won't lose 30 pounds in a month, but these small changes can make a big difference over time."

Changes can be also be profound if people focus on their immediate environment. As he points out: Families usually have a "nutrition gatekeeper" who, through shopping, cooking and serving food, controls about 73% of what everyone in the family eats.

Eating is strongly influenced by the environment, but each person can still exert some conscious control over it, says Dr. Harvey J. Widroe, a Walnut Creek psychiatrist and author of the 2007 book "The Smart Dieter's Cheating Guide." He tells his clients to start with a few simple principles, such as to eat only two-thirds of their usual portions or to replace a favorite food, such as ice cream, with a similar but healthier alternative, such as sorbet.

"People can do this," he says. But environmental changes, such as taking vending machines out of schools and office buildings, won't work. "People cheat. They'll find a way to eat."

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shari.roan@latimes.com