Sour cream stays fresh for three weeks, max
Q. I am wondering as to how many days after it is opened, but kept refrigerated, sour cream can be used safely.
D.G., San Diego, Calif.
A. Assuming it was refrigerated properly and opened before the freshness date stamped on the carton, your sour cream should last from one to three weeks.
A number of factors will influence where any given container will fall in that range. The time away from refrigeration should be kept to a minimum. A shopping trip to purchase refrigerated/frozen foods should be the last stop before returning home, and food should be unloaded and stored promptly.
When it's being used, the container should be resealed and returned to the refrigerator after any contents were removed; the fewer the openings, the better. Storage life decreases if contents are removed and then returned to the container after sitting at room temperature. It's also a risk if utensils used for other items are used to remove the sour cream.
A factor outside your control is whether the product was refrigerated properly along the way from production to your store. These are only guidelines. Any strange growth or pinkish color, off flavors or odors are grounds for immediate disposal. If you find great variability in the quality and shelf life of your refrigerated goods from a particular store, there may be issues with that store's equipment. The U.S. Department of Agriculture has a summary sheet of safe food handling at tinyurl.com/6cemnh.
Q. I have had problems with my thyroid and had a part of my thyroid removed. I now take thyroid medication and was wondering whether taking soy products like soy milk, etc., will affect the thyroid medication.
K., Tallahassee, Fla.
A. The hormones produced by the thyroid gland regulate the metabolism in every cell of the body. If, for any of a number of reasons, a person does not produce a sufficient amount of thyroid hormone, they can be given a medication that stimulates increased production by the thyroid gland, or one that serves as a replacement for the hormone itself.
Iodine plays a role in the synthesis of thyroid hormone, and isoflavones are a class of phytochemicals found in soy that can make iodine less available to the body.
A study in the March 2007 issue of the Journal of Medicinal Food 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. (Although it can vary from product to product, 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.)
The June 2008 issue of the Journal of Nutrition 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, where soy products represent a large proportion of the diet. Regarding iodine, the Daily Value is 150 micrograms. There is additional information on iodine at tinyurl.com/5ag27m.
Your issue is with thyroid medications, and some need to be taken on an empty stomach to avoid potential interactions with foods, dietary supplements or other medications, such as antacids. Always follow the instructions for this or any medication. Be sure to consult your family physician or a pharmacist if you have further questions.
• Ed Blonz, Ph.D., is a nutrition scientist and the author. Write him at "On Nutrition," Ed Blonz, c/o Newspaper Enterprise Association, 200 Madison Ave., New York, NY 10016 or ed@blonz.com. Due to the volume of mail, personal replies cannot be provided.