150 years of anecdotal evidence and observation suggest that carbohydrates are uniquely fattening, it would be unjustifiable scientifically to reject that hypothesis without compelling evidence to the contrary. Such evidence does not exist. There is a more important issue than how many calories, and it extends far beyond the ideal weight-loss diet. Prior to the official acceptance of the low-fat-is-good-health dogma, clinical investigators, predominantly British, had proposed another hypothesis for the cause of heart disease, diabetes, colorectal and breast cancer, tooth decay, and half-dozen or so other chronic diseases, including obesity.
The hypothesis was based on decades of eyewitness testimony from missionary and colonial physicians and two consistent observations: that these diseases of civilization were rare to nonexistent among isolated populations that lived traditional lifestyles and ate traditional diets, and that these diseases appeared in these populations only after they were exposed to Western foods, in particular, sugar, flour, white rice, and maybe beer.
These are known technically as refined carbohydrates, which are those carbohydrate-containing foods, usually sugars and starches, that have been machine-processed to make them more easily digestible. In the early 1970s, the hypothesis that refined carbohydrates cause heart disease and other chronic diseases competed directly with the dietary-fat hypothesis of heart disease. Carbohydrates could not cause heart disease, so the argument went, because fat seemed to cause heart disease. Moreover, any diet that contained a suitably low proportion of calories as fat would, by definition, be high in carbohydrates, and vice versa.
The only caveat was that the fat hypothesis was, indeed, only a hypothesis, and the evidence to support it was ambiguous at best. By the mid-1970s, the carbohydrate theory of chronic disease had been transformed into a more politically and commercially acceptable version: it wasn’t the addition of refined and starchy carbohydrates to the diet that caused chronic disease, but the absence of fiber or roughage, removed in the refining process, that was responsible.
This conclusion, however, has not been supported by clinical trials, which have shown that fiber has little or no effect on the incidence of any chronic disease. We have come to accept over the past few decades the hypotheses, and that is what they are, that dietary fat, calories, fiber, and physical activity are the critical variables in obesity and leanness in health and disease. But the fact remains that, over those same decades, medical researchers have elucidated a web of physiological mechanisms and phenomena involving the singular effect of carbohydrates on blood sugar and on insulin, and the effect of blood sugar and insulin, in turn, on cel s, arteries, tissues, and other hormones, that explain the original observations and support this alternative hypothesis of chronic disease.
The USDA statistics of how many calories we consume were based on guesses, not reliable evidence. These statistics, published yearly, estimate how much we consume each year of any particular food, by calculating how much is produced nationwide, adding imports, deducting exports, and adjusting or estimating for waste. The resulting caloriess for per-capita consumption are acknowledged to be, at best, rough estimates.
The changing-American-diet story relies on statistics dating back to 1909, but the USDA began compiling these data only in the early 1920s. The reports remained sporadic and limited to specific food groups until 1940. Only with World War I looming did USDA researchers estimate what Americans had been eating back to 1909, on the basis of the limited data available.
These are the numbers on which the changing-American-diet argument is constructed. In 1942, the USDA actually began publishing regular quarterly and annual estimates of food disappearance. Until then, the data were particularly sketchy for any foods that could be grown in a garden or eaten straight off the farm, such as animals slaughtered for local consumption rather than shipped to regional slaughterhouses. The same is true for eggs, milk, poultry, and fish. “Until World War I , the data are lousy, and you can prove anything you want to prove,” says David Cal , a former dean of the Cornel University College of Agriculture and Life Sciences, who made a career studying American food and nutrition programs. Historians of American dietary habits and how many calories we consume have inevitably observed that Americans, like the British, were traditionally a nation of meat-eaters, suspicious of vegetables and expecting meat three to four times a day.
Research from way back into how many calories we eat, according to the historian Lowenstein, estimated that Americans ate eight times as much meat as bread. By one estimate, the typical American was eating 178 pounds of meat annually, forty to sixty pounds more than was reportedly being eaten a century later.