Conditioning our minds/bodies for food intake/weight?

Hello, I was wondering if that idea about "if we eat less, our bodies will want less food, and likewise if we eat more and more, our bodies will want more food and take longer to get full, etc." is true. Can we really condition our bodies/mind in this respect? Is this a myth that has been debunked, or is this scientific fact? Are we as humans designed to eat a lot due to our genes telling us so? If we CAN condition our bodies, is this even healthy? Please reply back, thank you!