Physical activity is the real crux, but eating habits are important too, better educating people at adjusting their calories intake to their real needs and level of physical activity.

But the problems are more complex than this, for example there's the great decline in home cooking skills to address as well. Most western nations had a great knowledge and skills baggage developed over centuries and more, but since the 30s/40s it's seriously undermined (in the US, it's reached a critical level in some demographics). The lower those skills have become, the more complicated and time-consuming making balanced home meals have become, increasing even more the reliance on industrial products in home cooking, and the use of ready-made meals. And this covers everything, from the kitchen basics to having lost the traditional skills to make food tasty without abusing on salt, fat and sugar.