Ed Sammarco, age 12, of Youngstown, Ohio, for his question:

How does the body form fat?

When a reducing diet is recommended, a person is advised to cut out candy and starchy foods. This seems illogical. The basic food categories are fats, proteins and carbohydrates, which include starches and sugars. Surplus poundage is fat and cutting out the carbohydrate foods seems like the wrong way to reduce it. Nevertheless it works. It works because the body has its own complex system for remodeling different types of food.

Some of the fatty foods we eat are reduced to fine droplets and sent into the blood stream. The busy cells convert most of them into energy. Others are used to repair and build certain tissues. Some are exchanged with fats stored under the skin, around kidneys and in other normal fatty deposits. Some are stored to provide energy between meals. If we eat more food than the body can use, it converts the surplus carbohydrates and even proteins into fats. In this form, the surplus is easier to store. In case of diet or famine, this stored fat is converted to energy and used up.

All this fatty chemistry is called lipid metabolism    and lipid metabolism is a very complex operation. It is possible because foods are made of molecules and the atoms in molecules can be rearranged to make different molecules. To trigger these molecule miracles, the body uses hormones secreted by the glands, digestive juices and a wide assortment of other enzymes. The creation of body fat begins after the digestive system breaks down a meal into simple chemicals  ¬including amino acids and fatty acids, glucose and glycerol.

These simple ingredients are made mostly of carbon, hydrogen and oxygen atoms. The various starchy and sugary carbohydrates are made entirely of these three ingredients. The many types of sugar and starch differ because of the number and arrangement of atoms in their molecules. The body can separate these atoms and rebuild different molecules to suit itself. Fats have the same main ingredients, with more hydrogen. But a fat molecule has two parts. One part may be a molecule of glycerol, an arrangement of three carbon and three oxygen atoms amid eight atoms of hydrogen. On one side, three pairs of hydrogen and oxygen atoms are ready to complete the fat molecule. They form links with one, two or three of those fatty acids digested from the food.

This is how the body forms fat, molecule by molecule, from such foods as starches, sugars and proteins. There are many types of fat, depending upon which of the assorted fatty acids are linked to the molecules. The body needs many of them as fuel for energy. All surplus food matcrials are converted into fat and stored in special cells. Most of the fat deposits are under the skin. They form a tissue of thin walled cells. When stuffed full, the blobs of fat push the nuclei to the cell walls. As the body needs fat molecules, it uses those in storage and replaces them with newer ones. When the diet is reduced, there are fewer replacements and the stores of surplus fat are reduced.

Nowadays, it's stylish to be skinny and certainly the body is healthier without massive wads of surplus fat. However, crash diets put a big strain on the body. It deserves a slow and easy readjustment. Also, remember, a quota of fat is needed for many biological processes and normal fatty deposits act as insulators and cushions. Only the brain and parts of the central nervous system need no fat at all.