(From page 321-2) 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. 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 foods in such small quantities that nutritionists have considered it insufficient and the question is whether this quantity is indeed sufficient for good health. Once James Lind demonstrated that scurvy could be prevented and cured by eating fresh fruits and vegetables, nutritionists assumed that these foods are an absolutely essential dietary source of vitamin C. What had been demonstrated, they will say, is that scurvy is "a dietary deficiency resulting from lack of fresh fruit and vegetables." To be technically accurate, however, Lind and the nutritionists who followed him in the study of scurvy demonstrated only that the disease is a dietary deficiency that can be cured by the addition of fresh fruits and vegetables. As a matter of logic, though, this doesn't necessarily imply that the lack of vitamin C is caused by the lack of fresh fruits and vegetables. Scurvy can be ameliorated by adding these to the diet, but the original lack of vitamin C might be caused by other factors. In fact, given that the Inuit and those Westerners living on the Inuit's vegetable- and fruit-free diet never suffered from scurvy, as Stefansson observed, then other factors must be involved. This suggested another way of defining a balanced diet. It's possible that eating easily digestible carbohydrates and sugars increases our need for vitamins that we would otherwise derive from animal products in sufficient quantities.
Further on page 325:
Nutritionists would establish by the late 1930s that B vitamins are depleted from the body by the consumption of carbohydrates. "There is an increased need for these vitamins when more carbohydrate in the diet is consumed," as Theodore Van Itallie of Columbia University testified to McGovern's Select Committee in 1973. A similar argument can now be made for vitamin C. Type 2 diabetics have roughly 30% lower levels of vitamin C in their circulation than do nondiabetics. Metabolic syndrome is also associated with "significantly" reduced levels of circulating vitamin C, which suggests that vitamin-C deficiency might be another disorder of civilization. One explanation for these observations -- described in 1997 by the nutritionists Julie Will and Tim Byers, of the Centers for Disease Control and the University of Colorado, respectively, as both "biologically plausible and empirically evident" -- is that high blood sugar and/or high levels of insulin work to increase the body's requirements for vitamin C.
Aren't vitamin C levels low in people with MS, too? Much food for thought in Taubes' book!