Burning fat is difficult and metabolically “expensive.”
Burning sugar is fast and easy. Thus, when faced with an abundance of sugar, the human genome adjusts to down-regulate fat-burning machinery. This is the story of the 20th century, and the reason why 65% of adults in North America are overweight and tired.
The glycemic index and glycemic load numbers not only reflect the impact of the food on glucose balance, but also the degree to which that food suppresses the body’s ability to burn fat.