DEAR DR. BLONZ: These days, many of us who are getting up there in age are taking several prescription drugs, as well as dietary supplements. What's the total effect of all these substances? I have not been able to locate a resource where one can input all that he is taking to see how it may interact. Neither of my medical doctors have a clue, but they would also like to know about such a tool. Pharmacies can process this type of information, but only as it relates to prescription drugs. Throw in glucosamine, calcium, MSM, chondroitin and others, and it seems like no one knows! What are your thoughts? -- V.S., via email

DEAR V.S.: When prescription and over-the-counter (OTC) medications come to the marketplace, they have to go through FDA-mandated screening for potential interactions. Such is not the case with dietary supplements. In today's regulatory environment, what we have is a host of ongoing laboratory experiments where we are the guinea pigs. To be sure, not every combination is going to cause problems, but the risk is certainly there.

Consider that medications and dietary supplements -- even "natural" ones -- need to be metabolized and eliminated from the body. When multiple items are in the queue for processing, it can affect the way the body does its job, which can result in abnormal blood levels of medications that need to be tightly controlled. This, in turn, can lead to unexpected -- and possibly dangerous -- effects. Matters become even more complicated when multiple prescription medications, pre-existing health conditions, alcohol and who knows what else are also on the scene.

I am not saying that all supplements should be avoided, but the time has come when responsibility falls upon us, the consumers. My advice is to learn as much as you can. The Interactions Checker on drugs.com includes prescription medications and many dietary supplement ingredients. You can add your profile of products, and it will tell you where the red flags are. This is a good place to check before adding anything else to your regimen. Don't forget pharmacists, as they have the latest resources to help answer questions. Whenever you start a new medication, take the time to consult with your pharmacist to see if there are any issues with what you are already taking.

DEAR DR. BLONZ: My husband and I just turned 80 and we try to watch what we eat. After dinner, while we read or watch TV, we enjoy a small dish of ice cream. Is there anything wrong with this? -- H.L., Pleasanton, Calif.

DEAR H.L.: It is tough to provide specific dietary advice not knowing anything about the rest of your diet or health histories. With this as a qualifier, and making the assumption that you are in good health with a good lifestyle, there is absolutely nothing wrong with having ice cream; the key is the sum total of what we have for the entire day. With few exceptions, it doesn't pay to get worked up about individual foods. You are in the eighth decade of life, so you must have been doing something right. I encourage you to enjoy each other and enjoy your lives.

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: If I purchase tuna that is packed in water, will I get the same level of omega-3 fat that I would if I got the tuna packed in oil? -- M.M., Logan, Utah

DEAR M.M.: As a general rule, the oil used for canned tuna is either soybean or canola oil, not fish oil. Tuna in oil will contain extra fat, but little in the way of extra amounts of the healthful omega-3 fats. A 3.5-ounce serving of light tuna in water (drained) contains 0.8 grams of fat and 0.3 grams of omega-3 fats. Contrast this with light tuna in oil (drained), which contains 8.2 grams of fat and 0.2 milligrams of omega-3 fats.

For higher levels of omega-3 fats, use the albacore (white) tuna. A 3.5-ounce serving of water-packed albacore (drained) contains about 3 grams of fat, of which 1 gram is omega-3 fats.

Light tuna is made from the yellow fin and skipjack varieties, which contain less of the omega-3 fatty acids than albacore. One additional note about tuna: Because tuna is relatively high on the food chain, it can contain higher levels of contaminants such as mercury. It remains a flavorful, healthful fish, but it also makes sense to take steps to make good choices. When buying tuna, consider opting for tuna caught via troll, or pole-and-line. This will tend to be stated on the label. Check with the Seafood Watch (tinyurl.com/d464hdm) for more on the different types of canned tuna.

DEAR DR. BLONZ: What are the things in plant-based foods that prevent minerals from being absorbed? I'm concerned because my main source of calcium comes from vegetables and grains. -- R.R., Oakland, Calif.

DEAR R.R.: The compounds that limit absorption are known as chelators (KEY-late-erz) in that they bind, or chelate, nutrients -- in this case, minerals such as calcium and zinc. The two most common chelators are phytate, found in some whole grains, and oxalate, found in many fruits and vegetables, but most notably spinach and rhubarb.

Zinc deficiency was first described in people consuming a high-phytate cereal grain diet. It does not represent a problem when the grains are a part of a yeast-leavened bread, because yeast contains an enzyme that breaks the bond between the phytate and the mineral. That is not the case with an unleavened bread such as pita bread. Indeed, zinc deficiency tends to be prevalent in parts of the Middle East where pita bread accounts for about 85 percent of calories consumed.

There are plenty of reasons to enjoy spinach, such as its valuable phytonutrients, but its oxalate content means it should not be considered a good dietary source of iron and calcium (although it is high in both). Usually about 10 to 25 percent of the calcium in foods can be absorbed, but a study in the April 1988 issue of the American Journal of Clinical Nutrition reported that only about 5 percent of the calcium in spinach was actually absorbed. A second study two years later in the same journal reported that the calcium absorption in a low-oxalate vegetable, such as kale, was comparable to that found with dairy products.

If vegetables and grains are the core of your diet, make sure you include a wide variety of different food sources. Fruit and vegetable sources of calcium without significant quantities of oxalate or phytate include broccoli, turnip greens, collards, kale, mustard, figs and almonds.

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: Could you tell me if roasted or raw would make any difference with nuts, health-wise? What about the difference between oil roasting and dry roasting? One proponent of raw peanuts states that one half-cup of raw peanuts has 430 calories, but processed into peanut butter, a half-cup contains 780 calories. How can this be? -- S.S., Malibu, Calif.

DEAR S.S.: You are mixing volume with weight. There is space between those peanuts in the half-cup, which weighs about 73 grams. Contrast this with a half-cup of peanut butter, which weights 129 grams. If you were to look at similar weights of these two foods, the caloric content would be comparable.

When you roast nuts, or any food for that matter, it can bring about flavor-enhancing chemical reactions. With nuts, this can be accomplished with or without oil. Dry roasting requires specially designed ovens and utilizes hot air. Salt, paprika or other flavorings can then be added if desired.

Although dry-roasted nuts contain no added oils, there will only be a nominal difference in overall fat content as compared to oil-roasted nuts. This is because half the weight of the nut, and over 70 percent of its calories, come from its fat content. A honey-roasted nut will contain less fat per serving because some of the weight is taken up by the sugary coating. In terms of nutritional value, the high heat process will destroy some of the folate and thiamin (vitamin B1), but the other nutrients are unharmed.

Raw peanuts will have a different taste from roasted ones, but a comparable fat content. One item of interest is a study in the October 2000 issue of the Journal of Allergy and Clinical Immunology, which reported that raw peanuts provoked less of an allergic response in sensitive individuals than roasted peanuts. However, as there raw peanuts carry a slightly higher risk of microbiological contamination, they are not recommended for individuals with compromised immune systems. Raw peanuts should be stored in the refrigerator. Only buy them from sources that sell a lot of them, and avoid places where the raw peanuts might have been sitting around for a long time in a bulk bin.

DEAR DR. BLONZ: Can you explain why the vitamins and minerals in a dietary supplement expire? What is the best way to store these products? -- S.H., Arlington Heights, Ill.

DEAR S.H.: Vitamins are reactive compounds that play an integral role in the chemical reactions that comprise our metabolism. Although mineral supplements tend to be quite stable, vitamins can slowly lose their potency over time. The factors that encourage breakdown are humidity, temperature and light. Formulas that contain fat-soluble nutrients tend to break down the fastest. The best way to store products is in a tightly sealed container in a cool, dark place. Many supplements include moisture-absorbing capsules or packets to help maintain product quality. Product expiration dates indicate when the vitamins can be assured of full potency -- assuming that the product has been appropriately stored.

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.