DEAR DR. BLONZ: Regarding your answer about the ability to smell asparagus in urine, you had said “the ability to perceive the odor is determined by one’s genes.” Whose genes? The person producing the urine, or the person doing the smelling? Along this line, my wife seems to have “smell genes.” She accuses me of not bathing and wearing dirty clothes the day after I have eaten a salad with Italian dressing on it. How common are these “smell genes” in the general population? -- F.M.

DEAR F.M.: My apologies for any confusion. A sulfur compound gets produced in all who consume asparagus; it comes from a normal breakdown of the asparagusic acid found in varying levels in asparagus. Certain genes are needed for an individual to detect this odor.

As regards the second part of your question, several alterations can occur in the sense of smell, ranging from anosmia (loss of the sense of smell) to dysosmia (alteration or distortion in the sense of smell) to hyperosmia (enhanced sensitivity to odors). Attention should be paid when there are unexpected changes in the sense of smell (or taste). I’m unsure if the situation you describe is one you have always had to live with, or if it is something that recently emerged. If the former, then the two of you have to rely on your own strategy. But if a change in your wife’s sense of smell (or taste) is something that developed recently, then consider having it evaluated medically. A physician can determine whether it is the product of some event or ongoing process that needs to be better understood. More on this at b.link/taste81.

DEAR DR. BLONZ: I read your advice about the tolerable upper limits of copper and zinc. Currently, I am taking supplements called PreserVision AREDS 2 by Bausch + Lomb. Although I don’t have glaucoma or AMD (age-related macular degeneration), my mother had both. I do have medical issues with my eyes, just not those suffered by my mother.

I am taking one pill a day, though the directions say to take two. Each pill contains 40 milligrams of zinc and 1 milligram of copper. The main reason I’m taking the one pill is that it also contains 5 milligrams of lutein and 1 milligram of zeaxanthin, but now I wonder if the zinc isn’t too much. Should I stop taking them? -- C.E., Freemont, California

DEAR C.E.: A key issue with zinc and copper arises when one is present, and the other is not. This is made worse if one is present in excessive amounts in the absence of the other. The AREDS 2 supplement provides both zinc and copper, so that issue does not present itself.

I thank you for this question, and I hope this serves as a clarification of the point, so that others who might be taking this or similar products will not be concerned. Also, give a read to this article on vision supplements: tinyurl.com/yxmybl7r.

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: A close friend who went to college in China introduced me to goji fruit and leaves, and suggested I use them in various ways. She continues to praise their health benefits, all of which she learned about while there, and now grows goji berry plants in her garden. After all this, I began to notice that there are goji dietary supplements available for sale, which claim many positive benefits from this food. I have seen promotional statements about antioxidant powers to help the immune system, and nutrients that fight against cancer, among other things.

Do you have information about goji and any of these advertised abilities? -- S.F., Poway, California

DEAR S.F.: Goji fruit is a type of berry also known as the wolfberry (Lycium barbarum) and is a member of the tomato family that is native to China. Goji grows and matures in the sun, and contains several nutrients, including some vitamins, minerals, phytochemical antioxidants and fiber. The same, however, can be said for other berries, and many fruits, vegetables and even some grains. As a general rule, any plant that grows in the sun will need a combined arsenal of protectants, either physical or phytochemical, to allow it to thrive from generation to generation in the oxidizing solar rays. No surprise that berries tend to be such rich sources of antioxidants.

Fruits and vegetables are important dietary assets, but there’s no scientific evidence that goji products have unique powers to cure cancer, boost the immune system, increase longevity or improve other bodily functions.

There is always a risk of information bloat being used to promote new, so-called “exotic” foods. Mangosteen, acai and noni are other foods that have received similar treatment. We get stories of indigenous peoples who have not suffered the ills of Western civilization, and some people assume that specific local foods are responsible. These usually tend to be promotional statements put forth by people who stand to benefit from the sale of the products. There may even be the allure of making money selling the products while you get discounts on your own purchases.

We are open to persuasion by marketing techniques that target health situations that affect our lives. Rather than being skeptical and objective and asking “Why?,” we get cajoled into asking, “Why not give it a try?” When you want to believe something because you hope it’ll help you or someone you love, you become an easy target.

Our country is an amazing melting pot. I find it wonderful when we learn about foods used in other cultures. Goji fruit appears to be a very healthful food, and can certainly be enjoyed as such. That being said, don’t forget that there are many local fruits and vegetables of comparable merit.

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: My 25-year-old daughter eats about 4 to 5 ounces of canned tuna packed in water every day for lunch during the week. Should there be any concern about the mercury in the tuna? -- C.M., Los Angeles

DEAR C.M.: I also enjoy eating tuna. It offers great protein, and is a source of essential fatty acids (EPA and DHA). But doing it every weekday is definitely pushing it. Your tuna-holic daughter should probably be expanding her menu for lunchtime sustenance, and some additional information will help with this realization.

The Environmental Protection Agency posts a list of resources at b.link/fish22. Next, the Food and Drug Administration has a page on mercury levels in commercial fish and shellfish at tinyurl.com/y5s3prt4.

More articles can be found online, from various sources, on other tuna-related topics: the environmental impact of overfishing, for example, and the effects of mercury on the nervous system. Knowledge is power, so you should consider all this information. Even if your daughter switches to a lower-mercury fish, keep in mind that a “lower level” of mercury is still not “no” mercury. So the advice to rotate foods still makes sense.

DEAR DR. BLONZ: There are many patches that one can buy to place on the bottom of their feet to cleanse the body. Please advise me if these can really work to help detoxify the body. Various ones say they remove heavy metals, improve circulation, combat fatigue and stress, jump-start the metabolism and promote a better night’s sleep. There is even mention of some sort of FDA approval. I bought one, and according to the literature, you place one on each foot every other night for 30 nights, then use about once every three weeks. -- S.F., Chicago

DEAR S.F.: What, no cure for cancer, obesity, high blood pressure and arthritis? Based on the lack of objective evidence supporting such claims, these products are unadulterated garbage. The idea that those claims have any approval from the FDA is also nonsense. Check out the discussion about the “The Detox Food Pad Scam” at b.link/foot28.

DEAR DR. BLONZ: What is it in asparagus that makes urine smell? It is now in season, and both my husband and I enjoy it, but I always notice a telltale odor the next time I visit the bathroom. I notice it only after eating asparagus. My husband doesn’t have the same problem, and we both eat the same asparagus. -- G.A., Augusta, Georgia

DEAR G.A.: Asparagus, garlic and onions are members of the lily family. These vegetables all have sulfur-containing compounds that can give rise to distinctive odors. With asparagus, the peculiar odor isn’t noticeable in the raw vegetable. Rather, it comes from metabolic byproducts that are eliminated through urine after the asparagus is eaten.

While these harmless, yet odorous, compounds are produced in everyone, the ability to perceive the odor is determined by one’s genes.

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.