We rarely repent of having eaten too little.

—Thomas Jefferson

Americans have long been consumed with losing weight, seemingly willing to suffer deprivation and to embrace each new diet that debuts—even if the "new diet" is simply a twist on an ages-old weight-loss plan. The fixation with weight loss is so longstanding that even the word diet has assumed a new meaning. Used as a verb, diet means to eat and drink a prescribed selection of foods; however, in the twenty-first century "dieting" is synonymous with an effort to lose weight.

During the nineteenth century, fashionable body shapes and sizes varied from decade to decade, but most periods celebrated plumpness as a sign of health and prosperity and considered being thin a sign of poverty and ill health. At the turn of the twentieth century, rising interest...