Epidemiological studies advocate that high-fiber diets decrease the risk of type 2 diabetes, while data on Mediterranean diets, fat quality, minerals, vitamins, micronutrients and phytochemicals are inconsistent in this matter. An increase in dietary fiber normally means more grains. However, most evidence favors soluble fiber from fruits and vegetables, while insoluble fiber, which is dominant type of fiber in grains, seems less beneficial
A possible drawback of whole grains and beans is their content of plant lectins. The best studied cereal lectin is WGA, while gliadin, which also has lectin properties, has barely been investigated. The wheat lectin binds strongly to the insulin receptor and activates it more intensively than insulin, and with a longer duration, a fact that suggests that it may cause insulin resistance. However, the significance of these findings for glucose tolerance is unclear.
Researches among birds show that cereals can influence glucose metabolism in a potentially negative way. Those species of birds that are natural seed eaters control their blood sugar differently compared with other birds, and can manage quite well after the insulin-producing process. Shortly after elimination, temporary insulin-dependent diabetes develops and insulin treatment is mandatory, but after a period of recuperation, insulin therapy is no longer needed to preserve normal blood sugar levels. In contrast, non seed-eating birds behave like humans and are frequently dependent on supplementary insulin after removal of the relevant cells. Now, why should seed-eating animals have this particular characteristic unless it is a defense against something in the seed that can eventually destroy their cells?