Peasants in different regions had differing diets and nutritional deficiencies. A monotonous diet of rice, for example, would lead to beriberi. A diet of maize would cause pellagra. Low protein and low energy diets would cause marasmus and kwashiorkor. There is abundant evidence in historical record and texts like Deuteronomy that these clinical entities occurred in the past. Source

Having said that, historical diets weren't necessarily as terrible as you might think. If you get most of your calories from wheat, for example, or potatoes, you won't have any shortage of protein in your diet.