DEAR DR. BLONZ: Is there any valid concern about soy products affecting thyroid hormones? I need to take them, and have read that soy can cause problems. -- K.K., Chicago
DEAR K.K.: Thyroid hormones regulate the metabolism of every active cell in our bodies. If, for any reason, a person does not produce a sufficient amount of thyroid hormone, they can be given a medication to stimulate increased production by the thyroid gland, or they can receive a replacement for the hormone itself. (A thyroid deficiency can be diagnosed by your physician with routine blood tests.)
The essential element iodine plays an integral role in the synthesis of thyroid hormone. Isoflavones, a class of phytochemicals found in soy, have an ability to make iodine less available to the body.
Does this mean that having soy could be a problem for you? There are a couple of studies I like to turn to on this topic. The first is from the March 2007 issue of the Journal of Medicinal Food. This study reported that adding soy protein isolate, at a level of 9 milligrams of soy isoflavones per 10 pounds of body weight, did not significantly affect the thyroid function in a population that had an adequate iodine intake. (Isoflavone content can vary from product to product, but 1 cup of soy milk contains about 20 milligrams of isoflavones. The amount in this study would be the equivalent of 2 quarts of soy milk per day for a 180-pound person.)
Next we have the June 2008 issue of the Journal of Nutrition, which contained a review article on soy protein, isoflavones and thyroid function. This paper concluded that soy may reduce the efficiency of thyroid hormone function due to an effect on iodine utilization, but it does not appear to be a problem if soy is consumed as a reasonable part of a mixed diet.
There could be a concern with infants and children if soy products represent a large proportion of their diet. Regarding iodine, the Daily Value is 150 micrograms. There is additional information on iodine at tinyurl.com/27g35fq.
Be sure to follow the directions that came with your thyroid medication, as some need to be taken on an empty stomach to avoid potential interactions with foods, dietary supplements or other medications like antacids. Consult your family physician or a pharmacist if you have further questions.
DEAR DR. BLONZ: How many days after it is opened can sour cream be safely eaten? -- G.T., San Diego
DEAR G.T.: Assuming it was refrigerated properly and opened before the freshness date stamped on the carton, your sour cream could last from one to three weeks. When it's being used, the container should be resealed and returned to the refrigerator after any contents are removed; the fewer the openings, the better. Avoid returning leftover portions to the container, and use a clean utensil every time you take some out. These are general guidelines. It is outside our control whether the product was refrigerated properly along the way from production to your store.
You should toss the product if you find any strange growth or pinkish color, off flavors or odors. Be alert if you begin to discover variability in the quality and shelf life of refrigerated goods from a particular store; there may be issues with that store's equipment or handling practices.
In general, a grocery run to purchase refrigerated/frozen foods should be the last errand before returning home, in order to minimize these foods' time away from the fridge, and cold foods should be unloaded and stored promptly upon arrival home.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.