Good Calories, Bad Calories

commonly used.”

What additionally complicates any assessment of the role of carbohydrate restriction in reducing diets is that the composition of a diet is never quite so simple as merely being high or low in carbohydrates or refined carbohydrates. Proteins, fats, and calories assume different roles depending on the diet. Also, carbohydrates in these diets can be restricted, but the standard thinking is that they have to remain sufficiently high so that the brain and central nervous system derive all their necessary fuel from this dietary source of glucose. Nutritionists will often insist that 130 grams a day of carbohydrates are the minimal safe amount in a human diet.

Though glucose is a primary fuel for the brain, it is not, however, the only fuel, and dietary carbohydrates are not the only source of that glucose. If the diet includes less than 130 grams of carbohydrates, the liver increases its synthesis of molecules called ketone bodies, and these supply the necessary fuel for the brain and central nervous system. If the diet includes no carbohydrates at all, ketone bodies supply three-quarters of the energy to the brain. The rest comes from glucose synthesized from the amino acids in protein, either from the diet or from the breakdown of muscle, and from a compound called glycerol that is released when triglycerides in the fat tissue are broken down into their component fatty acids. In these cases, the body is technically in a state called ketosis, and the diet is often referred to as a ketogenic diet. Whether the diet is ketogenic or anti-ketogenic—representing a difference of a few tens of grams of carbohydrates each day—might influence the response to the diet, complicating the question of whether carbohydrates are responsible for some effect or whether there is another explanation. (Ketosis is often incorrectly described by nutritionists as “pathological.” This confuses ketosis with the ketoacidosis of uncontrolled diabetes. The former is a normal condition; the latter is not. The ketone-body level in diabetic ketoacidosis typically exceeds 200 mg/dl, compared with the 5 mg/dl ketone levels that are typically experienced after an overnight fast—twelve hours after dinner and before eating breakfast—and the 5–20 mg/dl ketone levels of a severely carbohydrate-restricted diet with only 5–10 percent carbohydrates.)

For fifty years after William Banting publicized William Harvey’s prescription for a carbohydrate-restricted diet in 1863, the primary clinical disagreements were on the role of fat in the diet. Banting’s original prescription was a high-fat diet, but then it was modified by Harvey himself and by the German clinicians Felix von Niemeyer and Max Oertel into lower-fat, higher-protein versions, and by Wilhelm Ebstein into a version featuring still more fat. “The fat of ham, pork or lamb is not only harmless but useful,” Ebstein wrote.

The notion of a carbohydrate-restricted diet based exclusively on fatty meat was publicized after World War I by the Harvard anthropologist-turned-Arctic-explorer Vilhjalmur Stefansson, who was concerned with the overall healthfulness of the diet, rather than its potential for weight loss. Stefansson had spent a decade eating nothing but meat among the Inuit of northern Canada and Alaska. The Inuit, he insisted, as well as the visiting explorers and traders who lived on this diet, were among the healthiest if not the most vigorous populations imaginable.

Among the tribes with whom Stefansson lived and traveled, the diet was primarily caribou meat, “with perhaps 30 percent fish, 10 percent seal meat, and 5 or 10 percent made up of polar bear, rabbits, birds and eggs.” The Inuit considered vegetables and fruit “not proper human food,” Stefansson wrote, but they occasionally ate the roots of the knotweed plant in times of dire necessity.

The Inuit paid little attention to the plants in their environment “because they added nothing to their food supply,” noted the Canadian anthropologist Diamond Jenness, who spent the years 1914–16 living in the Coronation Gulf region of Canada’s Arctic coast. Jenness described their typical diet during one three-month stretch as “no fruit, no vegetables; morning and night nothing but seal meat washed down with ice-cold water or hot broth.” (The ability to thrive on such a vegetable-and fruit-free diet was also noted by the lawyer and abolitionist Richard Henry Dana, Jr., in his 1840 memoirs of life on a sailing ship, Two Years Before the Mast. For sixteen months, Dana wrote, “we lived upon almost nothing but fresh beef; fried beefsteaks, three times a day…[in] perfect health, and without ailings and failings.”

None of Stefansson’s observations would have been controversial had not the conventional wisdom at the time been—as it is still—that a varied diet is essential for good health. A healthy diet, it is said, must contain protein, fats, and carbohydrates, the latter because of the misconception that the brain and central nervous system require dietary glucose to function, and the debatable assumption that fresh vegetables and fruit, which contain carbohydrates, are essential to prevent deficiency diseases.

Because it is still common to assume that a meat-rich, plant-poor diet will result in nutritional deficiencies, it’s worth pausing to investigate this issue. The assumption dates to the early decades of the twentieth century, the golden era of research on vitamins and vitamin-deficiency diseases, as one disease after another—scurvy, pellagra, beriberi, rickets, anemia—was found to be caused by a lack of essential vitamins and minerals. This was The Newer Knowledge of Nutrition, as it was called by the Johns Hopkins nutritionist Elmer McCollum; it dictated that the only way to ensure all the essential elements for health was to eat as many types of foods as possible, and nutritionists still hold by this logic today. “A safe rule of thumb,” as it was recently described, “is that the more components there are in a dietary, the greater the probability of balanced intake.”

This philosophy, however, was based almost exclusively on studies of deficiency diseases, all of which were induced by diets high in refined carbohydrates and low in meat, fish, eggs, and dairy products. When the Scottish naval surgeon James Lind demonstrated in 1753 that scurvy could be prevented and cured by the consumption of citrus juice, for example, he did so with British sailors who had been eating the typical naval fare “of water gruel sweetened with sugar in the morning, fresh mutton broth, light puddings, boiled biscuit with sugar, barley and raisins, rice and currants.” Pellagra was associated almost exclusively with corn-rich diets, and beriberi with the eating of white rice rather than brown. When beriberi broke out in the Japanese navy in the late 1870s, it was only after the naval fare had been switched from vegetables and fish to vegetables, fish, and white polished rice. The outbreak was brought under control by replacing the white rice with barley and adding meat and evaporated milk. Pellagra, too, could be cured or ameliorated, as Carl Voegtlin demonstrated in 1914, by adding fresh meat, milk, and eggs to a pellagra-causing diet, which in Voegtlin’s experiments constituted primarily wheat bread, cabbage, cornmeal and corn syrup, turnips, potatoes, and sugar. Nutritionists working with lab animals also found that they could induce deficiency diseases by feeding diets rich in refined grains and sugar. Guinea pigs were given scurvy in a series of laboratory experiments in the 1940s when they were fed diets of mostly crushed barley and chickpeas.

This research informed the conventional wisdom of the era that fresh meat, milk, and eggs were what the Scottish nutritionist Robert McCarrison called “protective foods” (which is how they were known before Ancel Keys and his contemporaries established them as the fat-rich agents of coronary disease), but it also bolstered the logic that a “balanced” diet, with copious vegetables, fruits, and grains, was necessary for health. Because diets of mostly grains and starches, or diets of refined grains, fish, and vegetables, such as the Japanese sailors consumed, might be deficient in a vitamin or vitamins essential for health, nutritionists considered it a reasonable assumption that this might be true of any such “unbalanced” diets, including those that were made up exclusively of animal products.

What the nutritionists of the 1920s and 1930s didn’t then know is that animal foods contain all of the essential amino acids (the basic structural building blocks of proteins), and they do so in the ratios that maximize their utility to humans.^*94 They also contain twelve of the thirteen essential vitamins in large quantities. Meat is a particularly concentrated source of vitamins A, E, and the entire complex of B vitamins. Vitamins D and B₁₂ are found only in animal products (although we can usually get sufficient vitamin D from the effect of sunlight on our skin).

The thirteenth vitamin, vitamin C, ascorbic acid, has long been the point of contention. It is contained in animal