Good Calories, Bad Calories

In 2003, seven physicians from the Yale and Stanford medical schools published an article in JAMA that claimed to be the “first published synthesis of the evidence” in the English-language medical literature on the efficacy and safety of carbohydrate-restricted diets. These doctors concluded that the evidence was “insufficient to recommend or condemn the use of these diets,” partly because there had been no long-term randomized controlled trials that established the safety of the diets. Nonetheless, they did report the average weight loss from the trials that the authors had culled from the last forty years of medical research. “Of the 34 of 38 lower-carbohydrate diets for which weight change after diet was calculated,” they noted, “these lower-carbohydrate diets were found to produce greater weight loss than higher-carbohydrate diets”—an average of thirty-seven pounds when carbohydrates were restricted to less than sixty grams a day, as Pennington had prescribed, compared with four pounds when they were not.^*103

Accepting that high-calorie diets can lead to greater weight loss than semi-starvation diets requires overturning certain common assumptions. One is that a calorie is a calorie, which is typically said to be all we need to know about the relationship between eating and weight. “Calories are all alike,” said the Harvard nutritionist Fred Stare, “whether they come from beef or bourbon, from sugar or starch, or from cheese and crackers. Too many calories are too many calories.” But if a calorie is a calorie, why is it that a diet restricted in carbohydrates—eat cheese, but not crackers—leads to weight loss, largely if not completely independent of calories? If significant weight can be lost on all these carbohydrate-restricted diets, even when subjects eat twenty-seven hundred or more calories a day, how important can calories be to weight regulation? Wouldn’t this imply that the quantity of carbohydrates is at least a critical factor, in which case there must be something unique about these nutrients that affects weight but falls outside the context of energy content? Isn’t it possible, as Max Rubner suggested a century ago, that “the effect of specific nutritional substances upon the glands” might be a factor when it comes to weight regulation, and perhaps the more relevant one?

Look at this another way. When Bruce Bistrian and George Blackburn instructed their patients to eat nothing but lean meat, fish, and fowl—650 to 800 calories a day of fat and protein—half of them lost at least forty pounds each. That success rate held true for “thousands of patients” from the 1970s on, Bistrian said. “It’s an extraordinarily effective and safe way to get large amounts of weight loss.” But had they chosen to balance these very low-calorie diets of fat and protein with carbohydrates—say, by adding another 400 calories of “wonderful fruits and vegetables,” as Bistrian phrased it—they would then be consuming the kind of semi-starvation diet that inevitably fails: 1,200 calories evenly balanced between protein, fat, and carbohydrates. “The likelihood of losing forty pounds on that diet is one percent,” Bistrian said.

The bottom line: If we add 400 calories of fat and protein to 800 calories of fat and protein, we have a 1,200-calorie high-fat, carbohydrate-restricted diet that will still result in considerable weight loss. If we add 400 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.