DEAR DR. BLONZ: You always speak about the importance of eating whole foods, but I keep seeing articles about the fact that our soils have become depleted of minerals. This depletion makes our foods less adequate to provide the nutrients we need than they were in decades past. In the survey course I took in agriculture when I was in college, I do recall that plants require certain nutrients to grow to their proper size, shape, color, form and taste. If this is the case, then it would seem that all the produce I see at the marketplace would have to have had their essential nutrients or they would not have grown -- or at least they would not look very good. Are those articles based on solid information, or is what I recall from the class more correct? -- O.F., Carlsbad, Calif.

DEAR O.F.: Your class recollections are on solid ground. Plants act as miners, pulling the mineral elements out of the soil that they need to grow. If a mineral needed by the plant is unavailable, the plant will not grow. It is incorrect to think that today's fruits, vegetables or grains will provide any less of their essential nutrients than the same varieties would have provided in the past. Plants synthesize their own vitamins, so these will be there as the plant grows.

Another layer to this question is the fact that nonessential minerals present in the soil can also end up in a plant. Whole foods grown in iodine-rich or selenium-rich soils, for example, can have more of these nutrients than the same type of food grown in soils with lesser amounts of these minerals.

Aside from the essential elements, what gets pulled in can vary from plant to plant, and mineral to mineral -- even among different varieties of the same fruit, vegetable or grain. The plant's overall nutrient content can also vary according to the time of the growing season and the length of time the plant has had to grow. This means that a plant picked green may not have the same total nutrient content as one allowed to ripen "on the vine."

It is difficult to speak with any statistical certainty, because we don't have records of nutrient content from the produce of a hundred years ago. Based on what we know, however, it's likely that the amounts would be comparable. Nutrient data tables, such as those at the USDA database (ndb.nal.usda.gov), present an average of what would be expected in a particular food.

DEAR DR. BLONZ: If the body can only absorb a limited portion of the minerals in a supplement, say 50 percent, and a supplement claims to supply 100 percent of the RDA, does that mean that you have to take two times the dose to actually absorb the RDA? -- S.M., San Francisco

DEAR S.M.: Dietary recommendations take the body's efficiency of absorption into account. They reflect the average amount an individual should be eating every day to satisfy the requirement. If, for example, science determines that the average body should have 100 milligrams of a certain mineral every day, and research indicated that we only absorb about 50 percent this mineral when consumed orally, then the recommended daily allowance (RDA) for that mineral would be 200 milligrams per day.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Both of the organic half-and-half products at my store are ultra-pasteurized, while the standard brands (not organic) are just pasteurized. What is the difference? -- J.J., Santa Fe, Ariz.

DEAR J.J.: Pasteurization and ultra-pasteurization are both heat treatments designed to reduce -- but not eliminate -- the presence of potentially harmful microorganisms. The two differ in the amount and duration of heat used. Pasteurization heats a dairy product to 160 degrees Fahrenheit for 15 seconds, while ultra-pasteurization heats the product up to 280 degrees Fahrenheit for up to 3 seconds. The higher heat used in ultra-pasteurization eliminates more bacteria, and results in a more shelf-stable product. Once opened, however, both types of products require refrigeration. Ultra-pasteurization is not widely used because the high heat can affect flavor. The process is usually used on products such as half-and-half or whipping cream, but ultra-pasteurized milk can be found in remote areas, or in stores that don't sell a high volume of milk.

DEAR DR. BLONZ: I have been enjoying dried apricots with breakfast, cutting them up to have with my cereal. It was pointed out that the ones I typically use are soft because they have added sulfur dioxide, and that this is something bad. Is this something I need to avoid? The ones without the sulfur dioxide are dry, leathery and difficult to cut. What is sulfur dioxide, and what purpose does it serve? What other products contain it? -- C.R. Waukesha, Wisc.

DEAR C.R.: Sulfur dioxide belongs to the group of preservatives known as the sulfites. Other sulfite preservatives include sodium sulfite, potassium sulfite, sodium metabisulfite and potassium metabisulfite. All can be used to help keep fruits and vegetables looking fresh. They can prevent discoloration as well as the growth of unwanted bacteria, molds and yeasts. Sulfur compounds are also used to help sanitize containers that are used in fermented beverages.

Sulfites are routinely used in wines and in dried fruits such as apricots, raisins, dates and figs for their antimicrobial effects, which allow for a longer shelf life. Bacteria and molds need small amounts of water to grow, so, as you noticed, apricots without sulfites (or some similar preservative) need to be dried down to that leatherlike consistency to achieve a comparable shelf life.

Sulfites are not without negatives. Some individuals experience adverse reactions to these preservatives, with symptoms ranging from headache, hives and mild shortness of breath up to a rare life-threatening breathing difficulty. The FDA estimates that about 1 percent of the general public can react in some way, and as high as 5 percent of those with asthma. The FDA has banned the use of sulfites on fresh fruits and vegetables (except potatoes) and it has to be indicated on the label whenever a sulfite preservative is present. You have been enjoying your sulfite-preserved dried apricots, so this would not appear to be an issue for you.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: What is the propellant used in the nonstick cooking sprays, and how do the sprays work? Why are they more effective than merely spreading oil on the pan? I rely on these sprays when I stir-fry vegetables or when I roast a chicken. Is this practice as healthy as it's made out to be? -- S.T., New Orleans

DEAR S.T.: Nonstick cooking sprays contain a vegetable oil -- such as corn, soy, canola or olive oil -- plus lecithin, an ingredient from soybeans traditionally used to keep oil and water in solution together. Aerosol versions also contain a propellant gas. Although each uses oil, cooking sprays differ in their ability to form a thin, well-disbursed oil-lecithin film that stays between the cooking surface and the food. Some products also include very small amounts of a silicone compound and alcohol to prevent foaming and to facilitate the formation of the nonstick film.

Because the sprays use a minimum amount of oil, little fat is contributed to the meal. A one-second application -- an amount sufficient to cover a 10-inch skillet -- will contain less than one gram of fat. The Nutrition Facts label on many of these products have a "recommended serving" of a third of a second or less. Tough to pull off, but it does allow the manufacturer to claim the product supplies less than a half of a gram of fat per serving, which in turn allows the product to be labeled as "fat-free."

The ingredients should be clearly stated on the container so you can opt for a product that contains no more than the basic components. About the only safety issue would come from the fact that aerosol sprays require a compressed gas for a propellant. Some make use of hydrocarbons such as propane or isobutane, both of which can be highly flammable. Such sprays should only be used on cold surfaces and kept away from all flames. If a flammable hydrocarbon gas is used, there should be an appropriate warning label to this effect. You may be able to find a product that does not rely on flammable hydrocarbon gas propellants.

When using these sprays, shake well, as the ingredients need to be thoroughly mixed to work properly. An oft-ignored drawback from the use of these products is the waste contributed by the empty aerosol can. There are refillable pump sprays that limit this aspect, but the high pressure of the aerosol is what helps facilitate spray performance. If you go the homemade pump-spray route, you may have to experiment with oils, staying away from unfiltered oils with particulate matter that might clog the nozzle.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.