In medieval Belarus (10th–18th centuries), urban populations consumed terrestrial animal products such as meat and milk as their primary dietary components, while rural populations consumed cereal crops such as rye, wheat, oats, and barley as their primary dietary components, with animal products serving as a supplementary protein source in rural areas.

People who ate mostly meat and milk had higher levels of nitrogen in their bones because animal proteins contain more of a heavy nitrogen form than plant proteins. People who ate mostly grains had lower nitrogen levels in their bones because plants have less of that heavy form. The body uses the nitrogen from food to build and repair tissues, and the type of food eaten leaves a clear chemical mark in the bones.