Q: Against my advice, my daughter insisted on following one of those low-carbohydrate diets. She lost a lot of weight at the beginning, but then found the pounds coming off much more slowly. Fortunately, she found the diet so unpleasant that she switched to a more traditional regimen and is continuing to lose weight slowly. But why did the low-carbohydrate diet produce such dramatic effects at first?

A: It's fortunate that your daughter decided, on her own, to adopt a more sensible program. By doing so, she has raised her chances for building the type of dietary habits conducive to long-term weight maintenance.

Here's why she had rapid weight loss early in her low-carbohydrate diet: First, the diet provides less carbohydrate than needed by the body, which draws upon a limited reserve supply in the liver. Called glycogen, this carbohydrate is stored with considerable water, as much as three to four times its own weight. As it is removed from storage so, too, is this water, producing a sharp drop in weight.

In addition, restricting carbohydrate to less than 60 grams a day causes a loss of the minerals responsible for maintaining fluid balance. This leads to further fluid loss.

Usually this rapid loss of fluid begins within 72 hours of starting the diet and lasts for about 5 days. After that, real weight loss -- shredding stored fat -- occurs by creating a deficit of about 3,500 calories for each pound lost. And as your daughter may have found out, the return to a normal diet is accompanied by a rapid gain in weight, the result of both the restoration of electrolyte balance and the restocking of liver glycogen stores.

Q: Is it true that some ceramic dishes are a source of considerable amounts of lead?

A: Yes, but the potential danger should be kept in perspective. Neither lead nor cadmium pose any risk if the glaze is properly formulated and if the ceramic to which it is applied is heated to a high enough temperature. The problem occurs when proper procedures are not followed, and especially if the container is used to store acid foods for long periods. The acid interacts with the substances in the glaze, accelerating the release of lead.

In 1969, a California family suffered acute lead poisoning from drinking orange juice stored in a pitcher bought in Mexico. After that incident, the FDA began setting limits for the amount of lead that can leach from ceramic ware used to prepare, serve or store food. Since 1971, when the FDA established these so-called "action limits" for cadmium as well as for lead, thousands of samples of housewares have been tested.

In 1980, levels were tightened, and now vary with the size and shape of the product. The FDA is currently reassessing whether the limits should be made still more stringent. It is considering banning the use of lead on glazes for interior surfaces or items that come into direct contact with foods, especially if they are likely to be used for storage.

Since the FDA began its surveillance of the problem, large pottery producers in the United States and other countries have worked to comply with the agency's lead limits, and the pottery industry has made dramatic improvements. But as the FDA admits, such compliance is by no means uniform, and there is no way to tell by looking at it whether the glaze is safe. At present there is no requirement that the use of lead be declared on ceramic products or for certifying that it meets standards.

Evidence suggests, however, that commercial earthenware is not a problem. Still, the FDA continues to test both domestic and imported pottery, especially from countries with a history of violations. Pottery ordered by mail or brought home by travelers escapes FDA surveillance.

The environment does contain other sources of lead, such as lead solder, once used to join copper piping. But to lessen the risk of unwittingly getting lead from pottery, the FDA suggests several measures. First, avoid using ceramic containers to store food. Second, beware of ceramic products purchased in foreign countries. If you are unsure of whether glazes contain lead, use the pottery decoratively, but not to store or serve food.

Do not use antiques or collectibles to hold food or beverages (unless you want to go to the expense of having them tested for lead). Finally, beware of ceramics made by amateurs or those who produce pottery as a hobby.

Q: Do pickles have any nutritional value? Also, how much sodium do they contain?

A: About the only thing that can be said in the nutritional defense of pickles is that most are low in calories. A medium sour or dill pickle, approximately 4 inches long and 1 1/4 inches in diameter, contains a mere 7 calories. The notable exception are sweet gherkins, which are rich in sugar. A large gherkin, about 3 inches long and 1 inch in diameter, contains about 50 calories. This is as many calories as you would get from a half-cup of orange juice, a cup of cantaloupe balls or a medium yellow peach, all of which provide far more vitamins than pickles.

Orange juice and cantaloupe, for example, are both excellent sources of vitamin C, and along with peaches are rich in carotenes, which the body converts to vitamin A. In contrast, cucumbers contain just a small amount of either one.

It cannot be denied that many people enjoy the crunch of a good pickle, its lack of nutrients notwithstanding. But the process that converts cucumbers to pickles by holding them in a brine solution transforms a very-low-sodium food into one richly laden with it -- as much as 2 grams in a single large dill or sour pickle.

It is recommended that we cut down on sodium intake as a measure of protection against hypertension. In light of this, it is probably better to eat pickles in their natural state, as cucumbers, and save moderate amounts of pickles for special treats.

Q: Is it true that water from wells is potentially dangerous to young infants?

A: Unfortunately, it can be. A case reported in the Journal of the American Medical Association illustrates how it happens. An infant girl who had been breast-fed at first, began receiving supplementary feedings made with powdered-milk formula mixed with well-water. Although the infant was judged healthy at the time of her first checkup at 1 month, the mother reported that she had noticed transient blueness of the infant's hands and feet and around the mouth earlier.

The mother also noticed that the child sometimes had trouble breathing and had diarrhea and vomiting. The infant was given progressively larger amounts of formula and her condition worsened. Sadly, the symptoms were not recognized and the child died.

The problem was traced to well-water on the farm where she lived. Concentration of nitrate in that water was 150 milligrams per liter, 15 times higher than the 10 mg-per-liter maximum contaminant level set by the Environmental Protection Agency (EPA). The nitrates, converted to nitrites in the intestine, are absorbed into the bloodstream. There they link up with hemoglobin, the oxygen-carrying pigment in red blood cells, to form methemoglobin, a pigment that cannot carry oxygen to the tissues. Infants under 4 months lack adequate amounts of an enzyme necessary to convert the methemoglobin to hemoglobin. When methemoglobin levels rise too high, the infant becomes cyanotic.

In rural states such as South Dakota, Minnesota, Nebraska and Iowa, a large proportion of the population relies on water from individual wells. Those 100 feet or more deep are usually safe. However, if the wells are poorly constructed or located improperly, surface waters contaminated with nitrates as well as with chemicals or other microorganisms may infiltrate.

This is especially true of shallow wells, which are sometimes contaminated during flooding, when runoff may contain fertilizers from cultivated fields, and after a heavy rainfall following drought. Boiling will kill harmful bacteria, but only serves to concentrate nitrates.

Consuming well-water contaminated with chemicals or bacteria is particularly serious for pregnant women and young infants. Yet the problem is entirely preventable. Wells should be tested annually to ensure safety, especially before a new mother returns home with baby. If any question exists about the safety of the water, an alternative source must be used.

Q: Is it true that methylene chloride is used in some water processes for decaffeinating coffee? Is this considered safe?

A: Yes to both questions. The safety of methylene chloride as a solvent for caffeine has been extensively studied. In 1985, the FDA's conclusion was that any risk associated with using it to extract caffeine was so low "as to be potentially nonexistent."

Several methods are used to decaffeinate coffee beans. In the water method, the beans are first steamed to add moisture. Then they are soaked for a long time in a mixture of water and coffee solids. That process removes 97 percent of the caffeine. Finally, they are dried and roasted. During the soaking, noncaffeine solids which enhance the flavor are also, inadvertently, extracted. So some manufacturers reuse this extract with the next batch of beans, and methylene chloride may be used for this purpose. However, after the caffeine is extracted, the solution is steamed to remove the solvent.

Caffeine may also be removed directly by using methylene chloride, ethyl acetate (a substance found naturally in fruits and vegetables), carbon dioxide, or coffee oil. After direct extraction with methylene chloride or ethyl acetate, the beans are steamed to remove any remaining solvent, then dried and roasted. Again, the extract is mixed with water to remove caffeine. Both the solvent and the water extract may be used over again.

Oil expressed from coffee grounds is yet another solvent. Its effectiveness hinges on the fact that caffeine is water-soluble. Finally, carbon dioxide under high temperature and pressure may be used to extract caffeine. By that method, the beans are steamed to add moisture and draw the caffeine to the surface before the beans are exposed to the carbon dioxide.