Good Calories, Bad Calories

That obese people overeat, at least during periods of weight increase, Bruch said, had been “adequately established.” What she disagreed with was what had now become, thanks in good part to her own research, the conventional interpretation of this observation: that overeating is the cause of obesity, and that the logical treatment is underfeeding. “In the course of my observations,” she noted, “studying many obese people in great detail and following them over a long period of time, I have come to the conclusion that…overeating, though it is observed with great regularity, is not the cause of obesity; it is a symptom of an underlying disturbance…. Food, of course, is essential for obesity—but so is it for the maintenance of life in general. The need for overeating and the changes in weight regulation and fat storage are the essential disturbances.”

In 1973, when Bruch published Eating Disorders: Obesity, Anorexia Nervosa, and the Person Within, she was still struggling with this conflict between psychological and physiological factors in the development of obesity. She acknowledged the need to prescribe reducing diets, and much of her analysis focused on those interpersonal and familial relationships that might contribute to obesity and dietary failure. Yet, she could not escape the suspicion, implied by a growing body of research, that the cause of obesity is a “primary metabolic or enzymatic disorder.” And she acknowledged that it was still up to researchers to unambiguously identify the nature of the disorder. “Studies of human obesity,” she wrote, “are not yet able to differentiate between factors that are the cause of obesity, or the result of it.”

Chapter Seventeen

CONSERVATION OF ENERGY

The complicated mechanism of the body must be taken into consideration, and the ways it takes to reach its goals are not always the straight paths envisioned in our calculations.

MAX RUBNER, The Laws of Energy Conservation in Nutrition, 1902

BEFORE WORLD WAR II, the proposition that obesity was caused by overeating—the positive-caloric-balance hypothesis—was one of several competing hypotheses to explain the condition. After Hilde Bruch reported that obese children ate immoderately, and Louis Newburgh insisted that a perverted appetite was the fundamental cause of obesity, the positive-caloric-balance hypothesis became the conventional wisdom, and the treatment of obesity, as Jean Mayer observed, became the provenance of psychiatrists, psychologists, and moralists whose primary goal was to rectify our dietary misbehavior. Any attempt to dispute the accepted wisdom was treated, as it still is, as an attempt to absolve the obese and overweight of the necessity to exercise and restrain their appetites, or to sell something, and often both.

This conviction that positive caloric balance causes weight gain is founded on the belief that this proposition is an incontrovertible implication of the first law of thermodynamics. “The fact remains that no matter what people eat, it is calories that ultimately count,” as Jane Brody explained in the New York Times. “Eat more calories than your body uses and you will gain weight. Eat fewer calories and you will lose weight. The body, which is after all nothing more than a biochemical machine, knows no other arithmetic.”

For fifty years, clinicians, nutritionists, researchers, and public health officials have used this logic as the starting point for virtually every discussion of obesity. Anyone who challenges this view is seen as willfully disregarding a scientific truth. “Let me state,” said the Columbia University physiologist John Taggart in his introduction to an obesity symposium in the early 1950s, “that we have implicit faith in the validity of the first law of thermodynamics.” “A calorie is a calorie,” and “Calories in equals calories out,” and that’s that.

But it isn’t. This faith in the laws of thermodynamics is founded on two misinterpretations of thermodynamic law, and not in the law itself. When these misconceptions are corrected, they alter our perceptions of weight regulation and the forces at work.

The first misconception is the assumption that an association implies cause and effect. Here the context is the first law of thermodynamics, the law of energy conservation. This law says that energy is neither created nor destroyed, and so the calories we consume will be either stored, expended, or excreted. This in turn implies that any change in body weight must equal the difference between the calories we consume and the calories we expend, and thus the positive or negative energy balance. Known as the energy-balance equation, it looks like this:

Change in energy stores = Energy intake-Energy expenditure

The first law of thermodynamics dictates that weight gain—the increase in energy stored as fat and lean- tissue mass—will be accompanied by or associated with positive energy balance, but it does not say that it is caused by a positive energy balance—by “a plethora of calories,” as Russell Cecil and Robert Loeb’s 1951 Textbook of Medicine put it. There is no arrow of causality in the equation. It is equally possible, without violating this fundamental truth, for a change in energy stores, the left side of the above equation, to be the driving force in cause and effect; some regulatory phenomenon could drive us to gain weight, which would in turn cause a positive energy balance—and thus overeating and/or sedentary behavior. Either way, the calories in will equal the calories out, as they must, but what is cause in one case is effect in the other.

All those who have insisted (and still do) that overeating and/or sedentary behavior must be the cause of obesity have done so on the basis of this same fundamental error: they will observe correctly that positive caloric balance must be associated with weight gain, but then they will assume without justification that positive caloric balance is the cause of weight gain. This simple misconception has led to a century of misguided obesity research.

When the law of energy conservation is interpreted correctly, either of two possibilities is allowed. It may be true that overeating and/or physical inactivity (positive caloric balance) can cause overweight and obesity, but the evidence and the observations, as we’ve discussed, argue otherwise. The alternative hypothesis reverses the causality: we are driven to get fat by “primary metabolic or enzymatic defects,” as Hilde Bruch phrased it, and this fattening process induces the compensatory responses of overeating and/or physical inactivity. We eat more, move less, and have less energy to expend because we are metabolically or hormonally driven to get fat.

In 1940, Hugo Rony, former chief of the endocrinology clinic at Northwestern University’s medical school, discussed this reverse-causation problem in a monograph entitled Obesity and Leanness, which is easily the most thoughtful analysis ever written in English on weight regulation in humans.^*86 Rony’s goal, as he explained it, was to “separate recognized facts from suggestive evidence, and reasonable working hypothesis from mere speculations.” This set Rony apart from Louis Newburgh, Jean Mayer, and others who were more interested in convincing their colleagues in the field that their speculations were correct.

When Rony discussed positive energy balance, he compared the situation with what happens in growing children. “The caloric balance is known to be positive in growing children,” he observed. But children do not grow because they eat voraciously; rather, they eat voraciously because they are growing. They require the excess calories to satisfy the requirements of growth; the result is positive energy balance. The growth is induced by hormones and, in particular, by growth hormone. This is the same path of cause and effect that would be taken by