Q. A new carbonated soda has appeared on the market, advertised as containing 10 percent real juices. Does this make it nutritionally superior to the standard varieties? A There are two reasons why it is not significantly different from regular carbonated beverages. First, the amount of fruit juice concentrate is quite small, adding only three grams of carbohydrate to a six-ounce serving of the diet version of the soda. By comparison, six ounces of orange juice contains 20 grams of carbohydrate.

Second, the juices are listed in descending order of prevalence by weight. Neither of the first two (white grape and pear) is a nutritional powerhouse. The amounts of the third and fourth (lemon and lime concentrate) are too small to add appreciably to the Vitamin C content of the soda.

Thus, if you look on the nutrition-labeling panel, you will find that this newcomer, like all other carbonated beverages, contains less than 2 percent of the U.S. Recommended Dietary Allowances for protein and seven other nutrients.

Q. I have read a number of articles on weight control that talk about the importance of behavior modification. I still don't have a clear picture of what is involved. Can you fill me in?

A. According to Dr. Albert Stunkard, an expert on the use of behavior therapy for eating disorders, and his colleague, Dr. Howard C. Berthold, behavior therapy is better described than defined. In a recent article in the American Journal of Clinical Nutrition, they list five core characteristics of therapy.

One, there is the assumption that all behavior, abnormal or normal, is acquired and maintained according to certain definable principles. Two, people are better described by how they think, feel and act in specific situations (in other words, their behaviors) than by emotions such as hostility and insecurity. Three, the therapy itself specifies treatment measures as precisely as possible and uses the most objective measures possible to evaluate outcomes. Four, treatment is highly individualized, a characteristic not unique to behavior therapy but an indispensable element of it. Finally, there must be continuous and critical assessment of treatment.

In reviewing five widely read books on the subject, the authors found they could group the behavioral principles of weight loss into seven categories. The first three, the original elements of behavior modification programs, include stimulus control (measures such as shopping from a list, scheduling meals and snacks, and storing food out of sight), eating behaviors (doing nothing else while eating, putting down the fork between bites) and rewards (for example, planning specific rewards for specific behaviors). All are designed to limit the stimuli that might lead to excessive eating.

Later additions to the behavioral package include self-monitoring or detailed record keeping, nutrition education, physical activity and "cognitive restructuring." This involves helping individuals set reasonable goals and emphasize progress instead of shortcomings.

Q. Why do fats smoke?

A. Fats are composed of compounds called triglycerides, which contain three molecules of fatty acids attached to one molecule of an alcohol named glycerol. When heated to sufficiently high temperatures, some of the triglycerides begin to break down into their component parts. And with continued heat, the glycerol is actually dehydrated to a compound called acrolein, which has an unpleasant, pungent odor and is irritating to the eyes and mucous membranes.

The so-called smoke point, the temperature at which smoke rises continually from the surface, varies considerably from one fat to another. Butter and lard decompose rapidly, while oils like corn, sunflower, cottonseed, soybean and peanut are better able to withstand higher temperatures. This makes them the fats of choice for deep-frying. In addition, processing methods in general use in this country tend to maximize smoking points in cooking oils.

When frying fats are used over and over, several factors will change the smoke point. Overheating is particularly damaging, but free fatty acids accumulate even in fat that has not been overheated, and these continually lower the smoke point on subsequent heating. So, too, do food particles remaining in the fat.