Education and willpower only work to some extent. People have a natural lipostat that "tells" them how much they should eat, and it's very hard to eat significantly differently - either more or less. What exactly changes this lipostat is not well understood, though there are well-known cases: lithium and other psychoactive medications, thyroid hormones. It is extremely likely that specific diets (in the broad sense) can also affect this lipostat mechanism - either directly, or through effects on the gut microbiome.