Cheryl Holman., age 11, of Spokane. Wash., for her question:

What is protein?

Nutrition begins when we sit down to dine. Our eyes sparkle at the colorful salad, our noses savor the soup and our taste buds drool toward the ice cream. Our stomachs, however, are interested in the fat, carbohydrate and protein context concealed in these gratifying groceries.

The body uses protein rich foods to build and to rebuild its living cells. Young people need meat and dairy products to build growing muscles, and people of all ages need these protein foods to rebuild the body's tissues from day to day extra proteins  are used as fuel to provide us with peppy energy. However, we cannot see these basic food elements on the dinner table. They are invisible molecules among many other molecules in our food items.

Proteins are complex chemicals made by the plant world. There are many different types, but only about 20 of them are useful to the human body. Molecules are bundles of atoms, and all protein molecules contain atoms of nitrogen and carbon, hydrogen and oxygen. some also contain atoms of sulfur or phosphorus. Plants absorb these basic chemical elements from air, soil and water and assemble them into molecules.

These molecules are heavy more than l00 times heavier than molecules of sugar are simple fat. They are extremely complex  too complex to be made by scientists. each big protein molecule is assembled from smaller molecules of a few atoms. These smaller molecules.are chemicals called amino acids. When soaked in hydrochloric acid the big protein molecules break apart into these smaller amino acids.

The same thing happens whfn the body digests the proteins we eat in our foods. The tiny amino acids axe small enough to pass through the intestine walls to the blood stream. The daily quota goes to the tissuss where older chemical building blocks are exchanged for new ones. The body stores no protein and daily supplies are needed for constant tissue building and rebuilding.

Animals remake plant proteins into richer proteins that are more useful to the human body. Our best protein foods contain all of the 20 or so vital amino acids and most of these complete proteins are in lean meats, eggs and milk. some of the vital amino acids are lacking in even the most protein rich vegetables such as soybeans.

As the population graves, food becomes a major problem and the hardest problem is providing enough protein for the world of the future. experts say that we cannot supply enough meat, which is the best source of protein. Plans have been suggested for adding the missing amino acids to plant proteins. Concoctions made from soybeans and peapods, peanuts and coconuts, grasses and even water weeds could then be used as complete protein foods in the human diet.