Q. Is there any advantage to buying natural vitamins?

A. None. Vitamins are complex organic compounds that the body needs in minute amounts to perform countless essential functions. The original source of these nutrients is, of course, the food supply. And, for the vast majority of us who are in good health, the food supply should remain the major source of these nutrients.

When they were first discovered, all vitamins were extracted from food. Gradually, scientists identified their chemical structures and learned to produce them inexpensively in the laboratory. When a nutrient supplement is used, the body cannot tell whether the source of the compound is some exotic fruit or vegetable or the product of the chemist's laboratory.

Beyond that, it has been pointed out that while the label on a bottle of vitamins might state that the pills inside contain "rose hip vitamin C," only a small portion of the vitamin in that preparation may come from that source. The rest, like traditional vitamin preparations, is made in the laboratory. Yet the premium paid can be considerable.

Most of us meet our need for vitamins by eating a varied and balanced diet. However, for various reasons some people may want to take an additional multivitamin or multivitamin with mineral supplement. If you are in that group, you can rest assured that there is absolutely no advantage to buying vitamins advertised as "natural," despite any claim to the contrary.

Q. I have heard that including soup in a weight-reducing diet is a good idea, since it somehow helps with the process. Is that true?

A. It has been suggested that soup is a useful food because it may slow the eating rate and may help the dieter feel full. However, the decision to include soup in a weight-reducing diet is better made on the basis of personal taste preference than on any evidence that it promotes successful weight reduction.

A recent study compared the effects of including soup as part of a dietary plan in two groups of obese individuals who were given weight-reducing diets and taught behavior-modification techniques. Soup was a regular part of the diet plan for one of the two groups.

Subjects in both groups were weighed weekly and asked to keep food records weekly for six months. They also participated in 12 weekly and eight monthly one-hour group sessions.

After 12 weeks both groups had lost significant amounts of weight compared with a control group that had received no instructions to that point. The "soup group" lost an average of 17 pounds while the other group lost about 19 pounds. At the end of one year both groups had regained some weight, an average of about 2 pounds in the "soup group" and about 5 1/2 pounds in the other group, reducing the net weight loss for the two groups to 15 pounds and 13 1/2 pounds, respectively.

A number of soups contain very few calories, and for people seeking to maximize the volume of their meals at low-calorie cost, these can be pleasant additions to the diet. Unfortunately, many commercially available varieties are high in sodium. So if you do use these, it is a good idea to check nutrition labels and try to choose those that are low in both calories and sodium. Better still, make and freeze your own, relying heavily on herbs and spices and minimally, if at all, on salt for seasoning.

Q. Can you please tell me why sugar is used in such foods as bologna and frankfurters?

Q. Sugar serves two functions. It softens the harshness caused by the use of salt in curing meat, and in more mildly cured meats it intensifies flavor. Second, it helps stabilize color.

The amount of sugar used is actually quite small, and in most cases below the level at which a sweet taste is perceptible. It ranges from 0.1 percent to 3 percent of the finished product. That means that a one-ounce slice of cured meat would contain less than a gram, or under 1/4 teaspoon of sugar. In checking nutrient composition tables, it appears that most contain less than that amount.