Q. Several months ago, you wrote that there is no reason to believe that a vitamin supplement prepared from specially compounded natural sources is in any way superior to the synthetic version. From my own reading, however, I find that there is considerable controversy over that issue. It would seem to me that you might have been more accurate to offer your statement as an opinion rather than hard fact. Do you agree?

A. Scientific reasoning leads us to stand by our original statement. We certainly agree that whenever possible it's more desirable to get all the micronutrients we need, including both vitamins and minerals, from fresh and lightly processed foods in our diet rather than by taking nutritional supplements. We do, after all, get a lot more than Vitamin C when we meet our requirement for that nutrient by eating an orange instead of taking a pill.

However, we do not agree that there is any nutritional justification for taking vitamins produced from "natural" sources. The reason is that vitamins are simply chemical compounds whose function in body reactions depends on their unique structures. There is no evidence whatever that when the ascorbic acid in a pill comes from an ascerola cherry it is one bit more useful to the body than when it is produced in a laboratory from simpler compounds. That is why we find it impossible to justify, on nutritional grounds, paying a premium for vitamin supplements from "natural" sources.

Q. Is there a limit to the amount of fat that ground beef may contain?

A. In most cases there is. Meat ground in federally inspected packing plants may contain no more than 30 percent fat by weight. Such meat is labeled with a USDA inspection mark. And meat ground in state-inspected packing plants must meet the same standards.

In point of fact, however, virtually all ground meat we buy is ground in local supermarkets and that meat is not subject to federal regulations for fat content.

Most states and cities do set standards for store-packaged ground beef. You can determine whether your community has such standards and what they are from your state department of agriculture office listed in the phone book. In general, meat labeled "regular ground beef" contains no more than 30 percent fat, "lean" approximately 23 percent fat, and "extra lean" about 15 percent fat. 1982 The Washington Post Co.