Good Calories, Bad Calories

of carbohydrates to the 800 calories of fat and protein, we have a balanced semi- starvation diet of the kind commonly recommended to treat obesity—and we reduce the efficacy by a factor of fifty. We now have a diet that will induce forty pounds of weight loss in perhaps one in a hundred patients rather than one in two.

This striking contrast also relates to hunger. One obvious explanation for the failure of balanced semi-starvation diets is hunger. (Another, as I noted earlier, is that our bodies adjust to caloric deprivation by reducing energy expenditure.) We’re semi-starved, and so we eventually break the diet. We cannot withstand the “nagging discomfort,” as William Leith put it. This is why clinicians like Pena and Leith believed that the carbohydrate- restricted diets were more successful: their obese patients could eat whenever they got hungry and would sustain the diet longer. It’s why Per Hanssen in 1936 suggested that the 1,800-calorie carbohydrate-restricted diet was likely to make weight maintenance easier than a 900-calorie balanced diet. But, as Willard Krehl noted, the diet at 1,200 calories also abated hunger: the desire for food, he wrote, was “more than amply satisfied.” Bistrian and Blackburn were able to reduce or eliminate hunger even at 650 to 800 calories. Had hunger remained acute, as Bistrian said, it’s likely that the patients would have eventually cheated, and this would have thwarted the weight loss if they cheated with carbohydrates. If the cheaters reached daily for a few hundred calories of carbohydrates—say, a bagel or a couple of a sodas—they would be eating a balanced semi-starvation diet with its 1-percent success rate. The 50-percent success rate on the half-protein, half-fat diet suggests that these dieters do not feel hunger, or certainly do not feel it as acutely as they would had they been eating a diet that came with carbohydrates as well. “Isn’t the proof of the pudding in the eating?” asked Bistrian.

These observations would suggest that we can add 400 calories to a diet of 800 calories—400 calories of fruits and vegetables on top of our 800 calories of meat, fish, and fowl—and be less satisfied. But, again, this will happen only if the initial diet is protein and fat and the added calories come from carbohydrates. If we add more fat and protein, we have a 1,200-calorie carbohydrate- restricted diet that will satisfy our hunger. So is the amount of calories consumed the critical variable, or is there something vitally important about the presence or absence of carbohydrates? The implication is that there is a direct connection between carbohydrates and our experience of hunger, or between fat and protein and our experience of satiety, which is precisely what Ethan Sims’s overfeeding experiments had suggested—that it’s possible to eat up to 10,000 calories of mostly carbohydrates and be hungry at the end of the day, whereas eating a third as many calories of mostly fat and protein will more than satiate us.

Now take into account the experience of prolonged starvation. In 1963, Walter Bloom, then director of research at Atlanta’s Piedmont Hospital, published a series of articles on starvation therapy for obesity, noting that total starvation—i.e., fasting, or eating nothing at all—and carbohydrate restriction had much in common. In both cases, our carbohydrate reserves are used up quickly, and we have to rely on protein and fat for fuel. When we fast, the protein and fat come from our muscle and fat tissue; when we restrict carbohydrates, they’re provided by the diet as well. “At a cellular level, the major characteristic of fasting is limitation of available carbohydrate as an energy source,” Bloom wrote. “Since fat and protein are the energy sources in fasting, there should be little difference in cellular metabolism whether the fat and protein come from endogenous [internal] or exogenous [external] sources.” And this turns out to be the case. The metabolic responses of the body are virtually identical.

And, once again, there is “little hunger” during prolonged starvation. “In total starvation,” Keys wrote in The Biology of Human Starvation, “the sensation of hunger disappears in a matter of days.” This assessment was confirmed in the early 1960s by Ernst Drenick at UCLA, when he starved eleven obese patients for periods of twelve to 117 days. “The most astonishing aspect of this study,” wrote Drenick and his colleagues in JAMA, “was the ease with which prolonged starvation was tolerated. This experience contrasted most dramatically with the hunger and suffering described by individuals who, over a prolonged period, consume a calorically inadequate diet.” As the editors of JAMA suggested in an accompanying editorial, this absence of hunger made starvation seem to be a viable weight-loss therapy for severely obese patients: “The gratifying weight loss without hunger may bring about the desired immediate results and help establish a normal eating pattern where other dietary restrictions may fail.”

The implication is that we will experience no hunger if we eat nothing at all—zero calories—and our cells are fueled by the protein and fat from our muscle and fat tissue. If we break our fast with any amount of dietary protein and fat, we’ll still feel no hunger. But if we add carbohydrates, as Drenick noted, we’ll be overwhelmed with hunger and will now suffer all the symptoms of food deprivation. So why is it when we add carbohydrates to the diet we get hungry, if not irritable, lethargic, and depressed, but this will not happen when we add only protein and fat? How can the amount of calories possibly be the critical factor?

In the early 1950s, Alfred Pennington noted the paradoxes engendered by a diet restricted in carbohydrates and relatively rich in fat and protein, and described them as a “mighty stimulant to thought on the matter.” But this is not how the medical-research establishment has perceived them. Rather, the accepted explanation for the success of carbohydrate-restricted diets is that they work via the same mechanism as calorie-restricted diets—they restrict calories, creating a negative energy balance. Either they so limit the choices of food that dieters simply find it too difficult to consume as many calories as they might otherwise prefer, or they bore the dieters into eating less, or both. “Many individuals spontaneously and unconsciously reduce their energy intakes by as much as 30% when placed on low carb diets,” Johanna Dwyer, a Tufts University nutritionist, explained in 1985. They do this “because there is insufficient carbohydrate permitted for them to eat many common and highly palatable foods in which they might otherwise indulge.” So where’s the paradox?

“The fact remains that some patients have lost weight on the low-carbohydrate diet ‘unrestricted in calories,’” the AMA Council on Food and Nutrition conceded in 1973 in a critique of such diets. “When obese patients reduce their carbohydrate intake drastically, they are apparently unable to make up the ensuing deficit by means of an appreciable increase in protein and fat.” By this logic, weight loss on a diet “unrestricted in calories” does not represent a refutation of the hypothesis that calorie restriction itself—creating a negative energy balance—is the only way to lose weight, because it suggests that a carbohydrate-restricted diet is a calorie-restricted diet in disguise. And the sensation of hunger isn’t an issue, because it can apparently be ignored.^*104

This rationale, which has been invoked frequently over the past four decades, is curious on many levels. First of all, it seems to contradict the underlying principle of low-fat diets for weight control and the notion that we get obese because we overeat on the dense calories of fat in our diets. One reason that bread has always been considered the ideal staple of a low-fat reducing diet, as Jean Mayer noted, is that it only has about sixty calories a slice. “If you put a restaurant-size pat of butter on your toast, for example, you triple the calories,” Mayer said. If we avoid the dense calories of fat in the butter, the argument goes, we will naturally eat fewer total calories and lose weight accordingly. (This was the fallback position in 1984 for the official NIH recommendation of a low-fat diet for heart disease: if nothing else, we’d lose weight on such a diet, and so that would reduce heart-disease risk.) To explain the peculiar efficacy of carbohydrate-restricted reducing diets, the circuitous reasoning is that if we avoid the not-nearly-so-dense calories of bread and potatoes, we will also not consume the dense calories in the butter. We could still eat the dense calories of meat, cheese, and eggs, and we could certainly increase the portion sizes to compensate for the now absent butter, but apparently we won’t want to do that, or somehow won’t be able to, if we don’t have the bread, potatoes, and pasta to eat as well.

Ironically, this argument is based almost exclusively on the research efforts of John Yudkin. “Yudkin showed that a long time ago,” as George Bray recently said. “We don’t generally slice butter off a dish and put in our mouth to eat. We like to put it on bread. That’s why lowering carbohydrates lowers calorie intake.” Yudkin was ridiculed for his advocacy of the hypothesis that sugar causes heart disease. Yet he is considered the essential source for the rationale that reconciles carbohydrate-restricted diets with the conventional wisdom of calories and weight, based