Human Nutrition, study of how food affects the health and survival 
of the human body. Human beings require food to grow, reproduce, 
and maintain good health. Without food, our bodies could not stay 
warm, build or repair tissue, or maintain a heartbeat. Eating the 
right foods can help us avoid certain diseases or recover faster 
when illness occurs. These and other important functions are fueled 
by chemical substances in our food called nutrients. Nutrients are 
classified as CARBOHYDRATES, PROTIENS, FATS, VITAMINS and
MINERALS, and WATER.

Dietary Supplements 

The use of dietary supplements has skyrocketed in recent years. 
Increasingly, people are taking herbs and other “natural” substances 
in addition to vitamins and minerals. Nutritional supplements are not 
as strictly regulated by the government as drugs, however, and to use 
them wisely consumers should know about the risks and benefits 
associated with supplements. A special feature in the October 1996 
installment of the Encarta Yearbook explored this issue.

When we eat a meal, nutrients are released from food through 
digestion. Digestion begins in the mouth by the action of chewing 
and the chemical activity of saliva, a watery fluid that contains 
enzymes, certain proteins that help break down food. Further 
digestion occurs as food travels through the stomach and the small 
intestine, where digestive enzymes and acids liquefy food and muscle 
contractions push it along the digestive tract. Nutrients are absorbed 
from the inside of the small intestine into the bloodstream and 
carried to the sites in the body where they are needed. At these 
sites, several chemical reactions occur that ensure the growth and 
function of body tissues. The parts of foods that are not absorbed 
continue to move down the intestinal tract and are eliminated from 
the body as feces.


When patients cannot absorb enough food through their intestines, 
for reasons ranging from coma to intestinal disease or injury, the 
patients’ nutritional requirements can be met by feeding through a 
vein. Currently, prepared solutions of synthetic amino acids, lipid 
mixtures, and other nutritional elements are available for health 
care workers to use in intravenous preparations. Intravenous 
nutrition can now sustain a person almost indefinitely. However, 
the balance of nutrients must be carefully monitored and, as with 
any intravenous therapy, there is a risk of infection and blood 
clots. Sixty years ago, health care professionals were just 
beginning to learn what substances are required in such an 
intravenous solution and in what proportion they should be 
delivered. A 1940 Scientific American article details the 
beginning of intravenous nutrition.