In general, the reason why we need to consume this large amount of food during our lifetime is clear. It is primarily intended to provide building materials. No matter how strange it may seem on the face of it, we continue to build up and rebuild our organism till well into old age.
Throughout his life man’s hair and nails are growing; the erythrocytes, the red blood corpuscles, live for only two or three months; then they die and are replaced by new ones. The cells of the squamous epithelium live for an even shorter period, not more than seven days.
The molecules of each cell in the body are continuously being replenished. Some molecules are completely destroyed and new ones are synthesized in their place, whilst others are partially rebuilt. Some of the building materials become waste matter and can no longer be used. For this reason all organisms continually need a supply of new building materials.
Trouble immediately begins if a deficiency occurs. Lack of copper or iron will result in anaemia. Even bones, which seem so firm, are continuously being built up. If the food consumed over a long time contains no calcium, bones which have sufficient calcium will start to give it up to supply the organism’s other needs and themselves become soft and pliable.