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.

DEAR DR. BLONZ: I have a math issue regarding body weight and body fat. If a pound contains 454 grams, and there are nine calories per gram of fat, please explain how a pound of body fat is said to contain only 3,500 calories. You and many others use this figure but the math does not add up. -- D.L., Poway, Calif.

DEAR D.L.: There are indeed 454 grams in a pound, as you point out. So how do we come up with 3,500 calories from a pound of body fat when 454 x 9 = 4,086 calories? To start with, consider that fat is our most calorie-dense substance and it is capable of providing an energy equivalent to nine calories per gram. It is utilized as the primary form of energy storage because humans, like other animals, need to be mobile. Imagine the image of a human with energy stores in the form of carbohydrate or even protein; if such were the case our bodies would need to take up over twice the space they do now.

Getting back to the math problem, the answer rests with the fact that adipose tissue in the body is not 100 percent pure fat. This tissue contains a small amount of water and some structural material, accounting for close to 15 percent of tissue weight. It is this nonfat portion that helps explain why a pound of body fat is said to contain approximately 3,500 calories worth of stored energy.

DEAR DR. BLONZ: I was wondering what your thoughts were regarding the use of sports drinks as a beverage for active children. -- E.F., Oakland, Calif.

DEAR E.F.: I would not consider a sport drink to be a universal go-to beverage for children; water fits that description. Next might be a nutrient-rich 100 percent fruit juice, ideally one from any of a variety of berries. Sports drinks can be helpful for those involved with hour-plus workouts or athletic events, in that they can help replace the sodium and potassium lost through perspiration. A small amount of sweetener helps make the drink more palatable, and it provides a small boost of the type of fuel that is in short supply during an extended workout. You don't want too much sugar as that can work at cross purposes by slowing absorption. I also advise against giving exercising children any drinks that contain stimulants, such as caffeine.

The journal Pediatrics found that an effective beverage contained, per 8-ounce serving, 14 grams of sugar (6 percent carbohydrate) and 110 milligrams of sodium (18 mmol/l sodium). See tinyurl.com/h9nne for more information. This is the same formula found in Gatorade and some other sport drinks. Check the Nutrition Facts label on any products before you buy.

I recommend that you make your own sports drink from fresh juices. Such a beverage provides the same nutrients as store-bought sports drinks, but contains genuine flavors and the added benefits of the fruit's phytochemicals. My recipe can be found at tinyurl.com/krkj8mx. You know your child best, so you should adjust the recipe accordingly.

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: A friend of my daughter's has celiac disease and she will be coming for a holiday dinner. My question is: Do oats have to be eliminated from celiac diets, or is wheat the only problem? Is there any problem with the vinegar I might use in my salad dressing? -- S.P., Oakland, Calif.

DEAR S.P.: Gluten is a complex protein found in all forms of wheat, barley, rye and triticale, or any products that might be made from these grains, including modified food starches. Celiac disease, also referred to as celiac sprue, is an autoimmune disorder in which the body has an acute genetic intolerance to gluten. The intolerance is such that the presence of gluten causes severe intestinal inflammation, with the immune system damaging the small intestines in a way that prevents nutrients from being absorbed. Note that celiac disease is a different clinical entity from non-celiac gluten sensitivity, or gluten intolerance, where the body can experience transient negative gastrointestinal reactions to gluten without the severe intestinal tissue damage.

As regards oats and celiac, they were once on the prohibited list, but then there was some research indicating that individuals with celiac disease may be able to tolerate certified wheat-free rolled oats. There have been studies that conclude "yes" to oats, while others have concluded the opposite. There is then the issue of individual differences between celiac patients: Some tolerate oats while others cannot.

The essential element is that the oats have no cross-contamination from handling or processing in plants that also handle wheat or rye. Those with celiac disease should get assurances to that effect, either from the product label or directly from the manufacturer. Your acquaintance should talk about oats with the professional handling this aspect of her health care to decide whether an oat experiment may be in order.

As for vinegars, most tend to be made from other materials, including apples, corn, rice and grapes, and these have no gluten. One vinegar of concern is malt vinegar, as this has gluten-containing malt added. Again, you should check the label or with the manufacturer if you have questions.

For more information, check out the information page from the National Institutes of Health at tinyurl.com/385xee or the website of the Celiac Disease Foundation at celiac.org.

DEAR DR. BLONZ: Is it OK to mix soy and cow's milk together? I searched the Internet and found all kinds of conflicting answers. -- S.L., Moraga, Calif.

DEAR S.L.: Assuming no allergies are present, there's absolutely no problem that I am aware of. After reading your question, I did some Internet searches and found a lot of anti-soy misinformation on this matter, so I am glad you asked.

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.