By the time Sarah and her father had walked much of the way across the continent, they likely were far more fit than is now average and had acquired very high percentages of muscle mass. The greater the amount of muscle, the higher the caloric demands of the body. Second, the calculations don’t take into account the often bitterly cold environment in which Sarah, her father, and everyone in the Donner Party were operating. In those kinds of conditions, even lying in bed, the body requires far more calories than normal.
