DEAR DR. BLONZ: I am interested in your thoughts about my new method of storing sour cream in the fridge. After it has been opened, I put the top on tightly, but store it upside-down to prevent air from getting in. I keep the inverted container on a small plate to keep drips from making a mess on the refrigerator shelf. I can't tell you exactly how much this increases the storage life, but I haven't had to throw out any sour cream since I started doing this. -- L.S., San Francisco

DEAR L.S.: Air exposure is what needs to be controlled. Lids should provide a good seal after the inner liner has been removed prior to the first use. Turning the container upside-down in the manner you describe might make a better air seal, but there is that increased risk of leakage, and that could represent a tradeoff. Odors or other contaminants could be picked up and passed back to the sour cream using the seeped liquid as its conduit. The priority should be buying the right size container for your typical use pattern.

DEAR DR. BLONZ: Are canned beans as nutritious as dry beans? The canned kind is more expensive, but less work. -- C.C., Baton Rouge, Louisiana

DEAR C.C.: Canned beans are just as nutritious as the dry kind. Many commercial products have added salt, but giving the beans a fresh-water rinse will remove a lot of that sodium. There are also low- and no-salt varieties available.

DEAR DR. BLONZ: Isn't it a bit misleading for foods to claim to be "nonfat" when they can contain large amounts of sugar? Doesn't sugar just become fat in the body, anyway? -- T.T., Sacramento, California

DEAR T.T.: The body has a constant need for energy, but we eat only a few times per day. We typically take in more energy and nutrients than we need at the moment, so our human machine has a finely tuned ability to put excess calories away until needed. A very small amount of carbohydrate is stored in the form of glycogen, but the vast majority gets stored as fat -- the most concentrated form. Food labels deal with what is in the food, not what happens once it is in the body.

DEAR DR. BLONZ: I am a cat owner and know that taurine is essential for cats. But I keep seeing it in energy drinks, and wanted to know why. -- S.H., via email

DEAR S.H.: Taurine is a compound known as a sulfonic acid. You are correct that it is needed by cats, but it's not essential for healthy human adults, as our bodies are able to make what they need. (One exception is that there is preliminary evidence that high levels of taurine may provide some benefit for individuals suffering from congestive heart failure.) The presence of taurine in energy drinks lacks scientific justification, as it is the caffeine in these drinks that provides the kick. It is unclear what taurine provides aside from "curb appeal," especially given the small amounts present.

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 local natural foods store recently held a seminar on cooking oils. The talk favored olive oil over alternatives, but said that when you open any bottle of cooking oil, such as corn, safflower, canola or peanut, the oxygen in the air immediately begins spoiling the oil. They said this was a "hidden cause of disease." They advised refrigerating all cooking oils after opening. However, product labels make no mention of any need to refrigerate. What do you recommend? -- B.T., San Diego

DEAR B.T.: Of course it is true that air gets in when you open the bottle, and that the oxygen in the air participates in the oxidation reactions associated with spoilage. However -- and this is the key -- it's a slow process under normal conditions, and there is no basis or evidence to fear that your oil, or your body, is at risk.

You can keep oils at room temperature, but you should follow some simple guidelines: Stored oils should be kept out of the sunlight and away from heat. And always keep the container sealed when not in use. Avoid buying amounts in sizes greater than you typically use in three to four months. But if you do, consider splitting the large size into smaller portions, refrigerating the unused bottles until needed.

There's no problem with storing oil in the refrigerator, but if you decide to go that route, be sure to have a tight seal on the container to keep the oil from picking up any undesirable refrigerator odors. Some oils may become cloudy when refrigerated, but this disappears when they return to room temperature, and it's no reflection on the oil's wholesomeness.

Oils can go rancid if they are mistreated or stored in the wrong way. Rancidity does indeed occur when an oil reacts with oxygen, and aside from giving foods an "off" taste, the consumption of oxidized oil does represent a health risk. The greater the degree of unsaturation (double bonds), the greater the tendency to oxidize. Omega-3 oils, such as flax or fish oil, have more double bonds than other oils, so they are very susceptible to spoilage. This helps explain the nasty aroma of fish left at room temperature for an extended period of time.

Our body has to deal with unwanted oxidation on a regular basis, and we have a series of systems designed to handle it. There are antioxidants produced in our body, for example, which are supplemented by those we consume in our diet. Eating well makes it so that we don't have to sweat the small stuff.

DEAR DR. BLONZ: Since I began a new multivitamin, my urine has become very yellow. Is this normal? I drink plenty of fluids, so I am not dehydrated. Does the yellow urine indicate an excess of bilirubin, and is taking the vitamins a strain on my liver? -- T.F., Butte, Montana

DEAR T.F.: I will have to assume that you are in otherwise good health. You should be comforted by the fact that it is quite common for B vitamins to increase the yellowness of urine. It happens all the time. B vitamins are yellow, and they color urine as they pass out of the body via the kidneys. This is not a sign of strain on the liver or the production of excess bilirubin (a waste product from the breakdown of hemoglobin).

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: Do fruits and vegetables put in a blender have the same fiber value as if eaten normally? -- D.D., La Jolla, California

DEAR D.D.: There is no problem with the blender, as the fiber and nutrient values are the same. You are eating the entirety of the same foods that went into the blender. The physical breakdown that takes place in the blender may end up causing the food to spend slightly less time in your stomach, but the net effect of the fiber should be the same. The same could not be said for a juicer, in which the fibrous bulk gets separated from the food and is not a part of the final product.

DEAR DR. BLONZ: It was my understanding that there is a considerable difference between soybean oil and palm oil. A popular whole-grain cracker lists in its ingredients "soybean and/or palm oil." If there is a significant nutritional difference between these two oils, isn't this somewhat deceptive? The product even has a red heart symbol, saying it may help reduce the risk of heart disease. Why are they allowed to use this seal if one oil ingredient is of questionable health value? -- M.M., Humbolt, California

DEAR M.M.: There is nothing deceptive about an ingredient statement indicating that a product contains soy and/or palm oil. That red heart seal on the product is likely based on the fact that the cracker is made from whole grains, and that the food is low in total and saturated fat. The numbers on the Nutrition Facts panel would have to be accurate irrespective of the oil or oils used.

Your concern about palm oil is misplaced. Palm oil is about 49 percent saturated, 37 percent monounsaturated and 10 percent polyunsaturated. You may have been thinking about palm kernel oil. Although from the same plant, palm kernel oil is quite different from palm oil: Palm kernel oil is around 82 percent saturated, 11 percent monounsaturated and 2 percent polyunsaturated. If you enjoy these crackers, the either/or oil ingredient should not be a reason to cross it off your list.

DEAR DR. BLONZ: Is there a vitamin or mineral that can reduce the dark circles under my eyes? -- K.K., Sedona, Arizona

DEAR K.K.: Darkness under the eyes can be brought about by a number of factors. Perhaps the most common cause is a natural thinness in the skin under the eyes. The skin isn't darker in that area, but it is thinner, which makes it easy to see the vascular bed underneath. This trait can run in families, and it doesn't necessarily reflect any health problem. If one is fatigued, under stress, or affected by allergies, the skin can lose its natural vascular glow; when this happens, the thin skin under the eyes can take on a paler tone and make the underlying vascular bed appear more prominent. I am sorry to say that aside from any vitamins you already take for your overall health, I have seen no evidence that specific vitamins or minerals can eliminate this problem.

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.