Composition of Foods a subject that has engaged scientists for thousands of years. The first serious attempt to classify nutrients was as part of the medical doctrine of the four humours, itself based on the theory that all matter was made of four elements, air, fire, earth, and water. This theory was developed by the Greek philosophers Pythagoras and Empedocles in the 6th and 5th centuries BC and elaborated by galen (2nd century AD). The doctrine had great influence until quite recent times, but was essentially philosophical rather than empirical and did not illuminate the question: of what are foods composed?
