Other health experts say that view is too extreme. Individuals can exert control over their own environment and lose or maintain weight despite the temptation of venti lattes, super-sized French fries and all-you-can-eat pasta bowls, they say.
"The environment, I think, to a large extent explains the obesity epidemic," says Dr. Robert H. Eckel, a professor of medicine at the University of Colorado and past president of the American Heart Assn. "But should we change the environment to alter the obesity epidemic? And how much do we need to change it? Those are difficult questions. To blame it all on the environment is a mistake. There is individual responsibility."
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Eating on autopilot
To explain how so many people have become overweight, researchers start with the urge to eat.
Eating is an automatic behavior that has little to do with choice, willpower or even hunger, Cohen says. Her paper, with co-author Thomas Farley of Tulane University's Prevention Research Center, was published online last month in Preventing Chronic Disease, the peer-reviewed health journal of the Centers for Disease Control and Prevention.
Cohen and Farley argue that automatic behaviors can be controlled, but only for a short time (the reason most diets ultimately fail). A more effective approach, they say, would be to decrease the accessibility, visibility and quantities of food people are exposed to, and the environmental cues that promote eating.
The fact that most people cannot maintain a weight loss is proof that nutrition knowledge and willpower don't work, they and other researchers contend.
"We've thought for a long time that if we just suggested to people that there are negative effects from obesity and if we provided reminders, they would be able to gain control over their behavior and act healthy," says Wendy Wood, a Duke University psychologist who studies habits. "There isn't much evidence that works."
Instead, ample research demonstrates that much of human behavior is automatic. Studies of people keeping activity diaries show that about 45% of daily human behavior is repetitious and unthinking. In a study published recently in the Journal of Consumer Psychology, Wood showed that people fall back on their habits -- such as buying fast food -- even when they intend to do otherwise.
