Good Calories, Bad Calories

The Tokelau experience stands as an example. The current accepted explanation for the pattern of disease among the Tokelauans is that the increased sugar and flour in their diets caused metabolic syndrome, and in turn heart disease and diabetes, at least according to Scott Grundy, who is a nutritionist and specialist in the metabolism of blood lipids at the University of Texas Southwestern Medical Center and the primary author of the 2003 cholesterol guidelines published by the National Cholesterol Education Program (NCEP). This does not mean, however, that Grundy believes that Cleave’s saccharine-disease hypothesis of chronic disease is correct, or that Keys was incorrect. Rather, as he explained it, in the United States the situation was less straightforward than in Tokelau. “What you’re faced with,” Grundy said, “is a historical change in people’s habits. Going back to the 1940s, ’50s, and ’60s, people ate huge amounts of butter and cheese and eggs, and they had very high LDL levels [the “bad cholesterol”] and they had severe heart disease early in life, because of such high cholesterol levels. What’s happened since then is, there has been a change in population behavior, and they don’t consume such high quantities of saturated fat and cholesterol anymore, and so LDL has come down a great deal as our diets have changed. But now…we have got obesity, and most of the problem is due to higher carbohydrate consumption or higher total calories. And so we’re switching more to metabolic syndrome.”

Grundy’s explanation is a modern version of the changing-American-diet story, in this case invoked as a rationale to explain how metabolic syndrome could be the primary cause of heart disease today, while Keys’s hypothesis could still be correct, but no longer particularly relevant to our twenty-first-century health problems. Grundy’s explanation allows both Keys and Cleave to be right—by suggesting that their hypotheses addressed two different but relevant nutrition transitions—and therefore does not require that we question the credibility of our public-health authorities. His explanation might be valid, but it relies on a number of disputable assumptions and a selective interpretation of the evidence. It could also be true that we faced very much the same problem fifty years ago that we do today, and that a continuing accumulation of evidence exonerates the fats in the diet and incriminates refined, easily digestible carbohydrates and starches instead. The implications are profound.

The appropriate response to any remarkable proposition in science is extreme skepticism, and the carbohydrate hypothesis of chronic disease offers no exception. But looking at the hypothesis in the context of a concept called homeostasis, which is of fundamental importance for understanding the nature of living organisms, gives us great insight. Much of the progress in physiology in the mid-twentieth century could be described as the transferral of this “concept of the nature of the wholeness,” as the Nobel Laureate chemist Hans Krebs suggested in 1971, “from the realm of philosophy and theory of knowledge to that of biochemical and physiological experimentation.” Though physiologists were aware of this paradigmatic shift, clinical investigators studying chronic disease have paid little attention, which means that the greater implications of the fundamental idea of homeostasis have been slighted.

In the mid-nineteenth century, the legendary French physiologist Claude Bernard observed that the fundamental feature of all living organisms is the interdependence of the parts of the body to the whole. Living beings are a “harmonious ensemble,” he said, and so all physiological systems have to work together to assure survival. The prerequisite for this survival is that we maintain the stability of our internal environment, the milieu intérieur, as Bernard famously phrased it—including a body temperature between 97.3°F and 99.1°F and a blood-sugar level between 70 mg/dl and 170 to 180 mg/dl—regardless of external influences. “All the vital mechanisms, however varied they may be,” Bernard wrote, “have only one object, that of preserving constant the conditions of life in the internal environment.” (As the British biologist J.B.S. Haldane noted a half-century later, “No more pregnant sentence was ever framed by a physiologist.”) And this stability of the milieu intérieur is accomplished, Bernard said, by a continual adjustment of all the components of this living ensemble “with such a degree of perfection that external variations are instantly compensated and equilibrated.”