Classical conditioning (or learning by association).
People are told they look good when they lose a little weight. Dieting therefore becomes associated with feeling good about yourself. Eating causes weight gain and as a result anxiety. As a result eating becomes associated with anxiety. Or
Social Learning Theory (neo-behaviourist)
We see others on television and in the media being rewarded for their thin build. Successful women tend to be thin! Think of television presenters, newsreaders, pop stars, actresses, celebrities, WAGS…. Girls, particularly are exposed to this vicarious reinforcement (the rewarding of others) and imitate in order to be rewarded themselves.
Admiring glances and compliments following weight loss, act to reinforce the dieting behaviour, so the weight loss continues. This is an example of Thorndike’s Law of Effect which put into simple terms predicts that of all behaviours performed, those that are rewarded are more likely to be repeated.
It is worth mentioning that severe weight loss and abstinence from food also punishes parents, which to the adolescent can be very rewarding in itself.
Girls with interests in areas with the most reward for weight loss are the most likely to develop an eating disorder, for example dancers, gymnasts etc. Garner et…