Dear Dr. Blonz: I am hoping you will answer these questions about vitamins and minerals. Is it OK to take water- and fat-soluble vitamins at the same time? Should vitamin C be taken with foods that contain vitamin C, or is it just as effective taken alone or with water? Should calcium be taken alone or with other nutrients, such as vitamins E, C and the Bs? What's the best time of day to take vitamins? Thanks for all your help. -- G.T., Las Vegas

Dear G.T.: There is no problem taking water-soluble and fat-soluble vitamins at the same time. You can take vitamin C with or without C-containing foods. As a general rule, it is preferable to take supplementary vitamins and minerals at mealtime. When food is present, the body is more attentive to the digestive system, and its blood supply heads that way to pick up the incoming nutrients.

There are two key points to be raised here. The first is that it is more important that you get the nutrients than to be overly concerned about when during the day you get them. Second, and more on point, is the fact that it is the foods you eat that deserve the starring role. Supplements are just that: supplements. Taking supplements does not provide the equivalent of the whole-food symphony of substances produced by the plant for its growth, development and defense of the plant -- substances which then become available to benefit your body when you eat that food.

Dear Dr. Blonz: We found a couple of bottles of oil given as gifts that were tucked away in the cabinet. They have been on the shelf for approximately two years, kept away from heat and light. They are both top quality, extra virgin olive oils and have not been opened. Am I correct in thinking that they should present no problem when used? – O.S., San Jose, California

Dear O.S.: Unlike wine, oil does not improve in the bottle. An extra virgin olive oil will be at its best when first put in the bottle (or can), and it’s all downhill from there. Oils should be tightly covered and stored away from heat and light. An unopened container of a refined vegetable oil -- properly stored -- can maintain quality for about a year. Some oils, including extra virgin olive oils, claim they can last up to two years, so yours are certainly worth a check. But don’t wait! Given that they were stored properly after being opened, you have about six months. As a general rule, the more unsaturated the oil, the shorter the shelf life after being opened. Oils that have been sitting for questionable periods of time should get a sniff and taste test before being used. It is always best to buy your oil in containers that match an expected rate of use. To help you keep track, mark on the label the date of purchase, and the date the container was first opened.

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: Are bacteria used to make buttermilk, somewhat in the same way as yogurt? Is this what gives it the sour taste? If so, is it as good for your intestinal flora as yogurt? -- S.E., El Cajon, California

DEAR S.E.: Starting as a byproduct of traditional butter-making, “buttermilk” was the name given to the liquid left after all butter was churned out of fresh dairy cream. Old-fashioned churning was not a sterile process; the milk sugar, also known as lactose, came in contact with bacteria in the air and in the nonpasteurized cream. The bacteria would use the lactose as fuel and metabolize it into lactic acid, which gave the fluid its distinctive, tangy taste.

At present, dairy companies must follow a general recipe to call a product buttermilk, but there are different types and no requirements that specific bacteria must be used. Acidophilus and bifidus bacteria are often used to make yogurt and other cultured milk products, but these are not necessarily used to make buttermilk. They may be added to the product for commercial appeal, however. Check the label or call the manufacturer to find the culturing bacteria present in the buttermilk you’re considering.

Beneficial bacteria used to make any cultured product can have a positive effect on the intestinal flora. Given the fact that they subsist on the unabsorbed remnants from foods we eat, our flora tend to reflect our general food choices. Incidentally, while the “butter” in its name gives the impression that buttermilk is a high-fat food, most commercial dairies use skim milk to make their buttermilks. An 8-ounce glass of a typical buttermilk contains 92 calories and only 2 grams of fat.

DEAR DR. BLONZ: How does psyllium compare with oat bran as a source of dietary fiber to be used as a supplement? -- F.S., Oakland, California

DEAR F.S.: Psyllium comes from the seed of the Plantago plant, a native to India and the Mediterranean. Used as a laxative in India for centuries, psyllium is also the main ingredient in over-the-counter laxatives in this country. On a weight basis, soluble fiber makes up 75 percent of the psyllium seed -- compare this to oat bran’s 8 percent soluble fiber.

Studies have shown that the addition of psyllium to the diet can help lower elevated blood cholesterol levels. Shortly after these studies were published, psyllium began to appear in commercial breads and cereals -- similar to what occurred when the same effect had been reported for oat bran. Unlike oats, though, psyllium has little to offer besides soluble fiber. Oat bran is a good source of protein, magnesium, iron, zinc, thiamine and phosphorus.

Care should be taken when adding supplemental fiber, as there can be side effects such as bloating, cramps, diarrhea and gas. In addition, loading up on fiber can interfere with the absorption of nutrients. This is a particular problem with supplements such as psyllium, which provides no nutrients of its own. Medications may also be affected, so touch base with your doctor before you add large quantities of fiber to your diet.

Oat bran might be a slight favorite as a supplement. An optimal approach to increasing one’s daily intake of fiber is to make a gradual shift to a plant-based diet with plenty of fruits, vegetables, legumes and whole grains. Here, the fiber is a natural component of foods that have much more to offer.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 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 believe I heard, at some point in my schooling, that rinsing and draining canned vegetables reduces their sodium content as much as 25 to 30 percent. I have searched through everything I have (old textbooks, lecture notes, etc.) and cannot find a single reference. I can’t believe there isn’t something more recent than that! Do you know how much the sodium content is reduced when canned vegetables are rinsed? Are you aware of any research articles on this topic? -- L.K., Phoenix

DEAR L.K.: Salt, or sodium chloride, dissolves easily in water, so rinsing canned vegetables and beans will certainly reduce their sodium content. As for the exact formula or percent reduction for a particular food, it would depend on total sodium in the food, the amount of added salt and the volume of water exchanged.

There is no specific data that I am aware of that works for all products. But you should be assured that rinsing canned vegetables is an effective way to cut their sodium content -- perhaps as much as 40 percent in some cases. I hope this helps.

DEAR DR. BLONZ: I am a big fan of tomatoes, and understand they contain a healthy compound called lycopene. I know that cooked tomatoes contain more lycopene than raw, and it is recommended to consume cooked tomatoes (such as sauce with pasta or pizza). I also like sun-dried tomatoes. What is the comparable vitamin and mineral content of sun-dried versus fresh tomatoes? -- S.S., Sacramento, California

DEAR S.S.: Sun-drying reduces vitamin C and vitamin A, and, to a lesser degree, some of the other vitamins. But the mineral content will remain largely the same. As for the lycopene, it helps to understand that cooked tomatoes don’t contain any more lycopene than fresh. Rather, the lycopene is chemically bound inside the cell matrix of the fresh tomato plant, and the cooking process breaks the bond, thus making the lycopene more bioavailable (absorbed with greater efficiency). Given that lycopene is a fat-soluble substance, eating tomatoes with some fat can add to lycopene’s bioavailability.

Sun-drying isn’t the same as cooking, but from the standpoint of lycopene absorption, it’s probably better than having fresh. When the water is removed, the cells do shrink, and they can break, especially if heat is used during the drying process.

Go ahead and enjoy your sun-dried tomatoes, but be sure to give them a good chew. If the lycopene is what you’re after, eat them with -- or within an hour of -- a fat-containing meal or snack.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 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.