One aspect is speed. Eat white sugar you will quickly get an energy boost but whatever cannot be used will be stored. Eat a complex carb and it requires more

One aspect is speed. Eat white sugar you will quickly get an energy boost but whatever cannot be used will be stored. Eat a complex carb and it requires more steps to breakdown. That allows for a slower release of energy and less of a need to store. The digestive system is a pipeline of processes.