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).