Today's children may well become the first generation of Americans whose life expectancy will be shorter than that of their parents. The culprit, public health experts agree, is obesity and its associated health problems. Heretofore, the strategy to slow obesity's galloping pace has been driven by what the philosopher Karl Popper calls ''the bucket theory of the mind. '' When minds are seen as containers and public understanding is viewed as being a function of how many scientific facts are known, the focus is naturally on how many scientific facts public minds contain. But the strategy has...