Why do doctors say don't eat so much white grain food?

Moderation. White grains (white rice, white bread, white pasta, etc.) are simple carbohydrates. This type of carbohydrate, when digested, turns into sugar quickly. This rise in blood sugar will cause a corresponding rise in one's Insulin level. The rise in Insulin can result in hypoglycemia, or low blood sugar symptoms of feeling sluggish, tired, shaky, and weak. Moderation is best.