I grew up in France and I have always cleaned my plate as my mother told me. In my familly, it's the polite and sensitive way to eat. Same expectation when visiting friends. Really few are overweight.
Since I moved to Japan, I learned that here too food is treated with the same deference : "you shall not let a grain of rice left in your bowl" is basic table decency. Few overweigh people here either.
Both France and Japan have their food recognized as UNESCO cultural world heritages. In both countries people LOVE to eat and hate to waste.
Maybe people should treat their food and themselves with respect and only put on the plate what they should and can eat?