He wanted to see his girl-friend, so he ate less every day for a month and lost seven pounds. The causal factors of his behavior were hunger and sex. His perception was that he had free choice to eat or not eat. The determining factors of his behavior seem to be outside of him. Ask any dieter - there are major problems with gaining and losing weight and having control over eating.
Eating seems strongly influenced by a number of factors.
This model, and this question of freewill, is especially poignant for alcoholics. On the one hand, they often seem to have a physical predisposition toward alcohol consumption. There are many other influences as well, such as culture, peer, and habit. So staying away from alcohol becomes a supreme struggle. It is a battle the alcoholic can lose, and which can repeat over and over again.