Many people like eating unhealthy food even though they know it is bad for themselves. Why? What effective way can improve people's healthy eating habits?

Unhealthy eating persists not because people lack all knowledge, but because food choices are shaped by habit, stress, price, marketing and the environments in which people live and work. People continue to eat unhealthy food because it is convenient, rewarding and socially normal, and healthier habits require changes in both personal routines and public food systems.