For most Americans in the 19th century, it wasn't what you ate, but how much you ate, that mattered. Late in the century, doctors wrote books like How To Be Plumb and the voluptuous woman was the ideal. The famed actress Lillian Russell, considered by many the epitome of beauty, weighed almost two hundred pounds. Today, in contrast, Americans seem obsessed with calories, diets and slimness, and with eating healthful amounts of vitamins, minerals,...