Q. The last time I had my hair cut the hairdresser suggested that the feel of my hair indicated some type of nutrient imbalance. She offered to send a sample, at considerable cost to me, for laboratory analysis. I said no, but have been wondering about it ever since. Should I be concerned? Are some hairdressers now being trained to check for nutrient deficiencies?

A. Some beauty shops, as well as some health food stores, chiropractors, "nutrition consultants," and other practitioners, promote hair analysis both to provide valuable "clues" for the diagnosis and treatment of an array of diseases and as a basis for prescribing supplements. In fact, there are at least eight good reasons why multi-elemental analysis of human hair is considered an inappropriate tool to assess nutritional excesses or deficiencies. It cannot serve as a basis for recommending nutritional supplements. Moreover, the quality of the performance of the laboratories that conduct these analyses may leave something to be desired.

In a recent issue of the Journal of the American Medical Association, Dr. Stephen Barrett, editor of the newsletter Nutrition Forum, reported on his evaluations of this service. Each of the 13 laboratories that do these analyses were contacted by a "doctor" interested in using the service. In response, literature and instructions for preparing samples were sent.

Hair samples were then taken from two apparently healthy teen-age girls. Under assumed names, two samples from each girl were sent to each of the laboratories. The reported levels of most minerals varied considerably between identical samples sent to the same laboratory and from one laboratory to another. For most minerals, several laboratories reported values of at least 10 times those found by other laboratories. Five of the 52 reports suggested that lead levels, for example, were abnormal in one sample but not in the identical sample presented under a different name.

Even if the measures had been more accurate, standards given for what was considered normal varied considerably.

Six laboratories recommended nutritional supplements. Their advice about them was bizarre, including mixtures of minerals, vitamins, nonessential food substances, enzymes, and extracts of animal organs. The reports recommended an average of 6 supplements and 18 doses a day. Most of those that made diagnostic suggestions said that these were not intended for diagnosis or treatment but merely indicated "trends or tendencies." Yet their suggestions, such as "excessive tendency to neuromuscular problems" to an apparently healthy young woman would certainly alarm anyone who took the report seriously.

Your instinct to decline the offer of hair analysis was clearly appropriate.

Q. Could you please explain how liquid oils are hydrogenated?

A. Understanding hydrogenation requires a little knowledge about the chemical makeup of fats. Nearly all fats are composed of compounds called triglycerides, containing three chains of fatty acids attached to an alcohol called glycerol. The fatty-acid chains are strings of carbon atoms to which hydrogen atoms are affixed. When the carbon chain holds all the hydrogen it can possibly take on, it is said to be saturated. In that case each carbon is attached to the next by a single bond. When there is a "vacancy" along the chain, two carbons are linked to each other by a so-called "double bond." It is here at these double bonds that hydrogen is added to the fatty acid.

The process involves several steps. First the oil is mixed with a catalyst (usually nickel) to speed up the reaction. Then it is heated to a fairly high temperature, and finally it is exposed to hydrogen under pressure. During this step the oil must be agitated to help dissolve the hydrogen, insure thorough mixing of the catalyst, and aid in getting rid of the heat generated by the reaction. When the desired degree of hydrogenation has been achieved, the oil is cooled and the catalyst is filtered out.

Q. Can you please tell me what the additive called "alginate" is?

A. Alginates (there are many different compounds in use) are part of a large group of water-soluble gums that are extracted from both land and marine plants. They are used by the food industry because they contribute to viscosity or gelling ability. As you might guess from the name, alginates are derived from brown algae, and, more specifically, the main commercial source is a particular type of giant kelp.

Alginate compounds are used in ice cream to add body and texture and to prevent the formation of large ice crystals. In baked products they enhance texture and gelling in cake and pie fillings, meringues and icings. They are used to thicken and stabilize the emulsion in some commercial salad dressings. In ultrapasteurized cream an alginate is used to help restore its normal properties and allow it to whip properly. And finally, an alginate may be added at low levels to beer to stabilize the foam.