Good Calories, Bad Calories

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 Peña 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.”