Historical origins of obesity

"We are not adapted to handle fast-acting carbohydrates," Ludwig continues. "Glucose is the gold standard of energy metabolism. The brain is exquisitely dependent on having a continuous supply of glucose: too low a glucose level poses an immediate threat to survival. [But] too high a level causes damage to tissues, as with diabetes. The body is designed to keep blood glucose within a tight range, and it does this beautifully, even with extreme nutrient ratios: we can survive indefinitely on a diet of 60 percent carbohydrates and 20 percent fat, or 20 percent carbohydrates and 60 percent fat. But we never [before] had to assimilate a heavy dose of high-glycemic carbohydrates."