The Grapenuts are like salad to me. They're foods with less energy sold as healthy because most people's energy expenditure is below their intake. Try selling Grapenuts and salads to farm workers, and they will laugh in your face. It's no accident taco trucks sell dense energy for the price; their customers need that fatty meat and complex carb rice.
You could feed a nation with little energy to expend even less energy to digest, but that would only lower further the energy they expend.
You could feed a nation with little energy to expend more energy to digest, but will they expend it?
You could tell a nation with little energy to expend to expend more energy, but where does it come from?
I think people right now have plenty of energy that they are consuming. Sure, they could clean out their stomachs by lowering fiber intake and removing the difficult to digest stuff like grains. They could eat more meat, which has denser minerals and also improves mineral absorption to boot, a double whammy. They could even replace sodas and candies with more water and fruit.
I think we have a bigger "lack of energy expenditure" problem than a "lack of energy intake" problem. Of course, tell that to a white collar nation bent on creating more service jobs. The correct and easy way out is overlooked every day. Just work out more, or make your lifestyle a work out.