Thanksgiving has always been a day of delicious gluttony. According to the American Council on Exercise, the average adult consumes nearly 4,500 calories at the Thanksgiving table, which is about twice the recommended daily intake. Instead of listening to our stomachs, which were already full of mashed potatoes and turkey, we insisted on stuffing ourselves with the stuffing, too. And then there was the pie. It wouldn't have been Thanksgiving without a few slices of pumpkin pie.

Why...