Most people are well educated about healthy eating habits but lack the essential ingredient to putting the theory into practise: willpower. A feature in Appetite says food decisions are based two conflicting sets of norms, descriptive and injunctive.
University of Alberta researcher Robert Fisher says that while people know, for example, that eating cheeseburgers might be bad for us, the signs in our environment give us the green light to consume.
"Not only is fast-food advertising very prevalent, but you see fast food signs, restaurants and wrappers everywhere," he said. "I think as a result, our baseline notion of what is normal is also changing. It's a bigger part of our lives than it ever has been before and there's no going back."
He found that people with higher body mass indexes had stronger beliefs associated with the rules than people with lower BMIs. But people with higher BMIs actually had stronger beliefs in the normative rules related to eating - the missing element, he said, was not following their individual belief structures.
"It's not a knowledge problem. People know what they need to do. It's just doing it or being motivated enough to do it," said Dr Fisher. "It's really about changing behaviours.
"You have to be both willing and able to change."