However, Animal proteins are more complete and thus desirable. Knowledge of the nutrients and their function is essential to understanding the importance of good nutrition. As mentioned above, there are six nutrients. All vitamins are organic food substances that are found only in living things, plants and animals . It is believed that there are about twenty substances that are active as vitamins in human nutrition .
Every vitamin is essential to the proper growth and development of the body.
With a few exceptions, the body cannot make vitamins and must be supplied with them. Vitamins contain no energy but are important as enzymes which help speed up nearly all metabolic functions. Also, vitamins are not building components of body tissues, but aid in the construction of these tissues. It is impossible to reliably determine the vitamin requirements of an individual because of differences in age, sex, body size, genetic makeup, and activity. The RDA makes it's recommendations based on studies of consumption of the given nutrient.