Yang is more compact, inward, hot, kinetic energy, which comes from the Earth, salt, minerals, animal flesh, eggs and cheese, baked foods, etc.
Yin is upward and outward focused, potential energy, which comes from the sun, sugar, fruit, raw vegetables, beverages, bubbles, alcohol, chemicals and drugs, etc.
Our body is best when it creates balance, which is easier to do when we do not feed ourselves extreme yin and yang. More at http://www.macrobiotics.tv