Nutrients vary little among onion varieties
Q. Does the phytochemical content vary among different types of onions?
A. Phytochemicals are natural compounds found in plants that may offer protection from a variety of diseases, including cancer. Onions are major contributors to our consumption of the largest group of phytochemicals - flavonoids - that act as powerful antioxidants. Phytochemical content of plant foods always varies somewhat with growing conditions, but yellow and red onions tend to contain much higher levels of flavonoids such as quercetin, when compared to white onions, Vidalias and other sweet onions.
Like garlic and shallots, onions contain sulfur-containing phytochemicals that seem to provide protection at several steps during the process of cancer development. Researchers have not documented any differences in content of these sulfur compounds among different types of onions at this time.
You are best advised to choose your onions based on their intended use, rather than their phytochemical make-up. Yellow onions, by far the most common type, are full-flavored and great for cooking - especially when recipes require longer cooking times or when you want more flavor. Many chefs consider red onions best for use raw in salads or sandwiches, or for quick cooking recipes, like kabobs. White onions have a sweet flavor and are the classic choice for traditional Mexican cuisine.
Q. How much selenium do we need, and what foods supply it?
A. Selenium is a mineral and one of many antioxidants in our food supply that may help lower risk of cancer. While no dosage amount has been identified for its potential role in cancer prevention, the Recommended Dietary Allowance (RDA) for its role in normal cellular function is 55 micrograms (mcg) for adult men and women.
Seafood, meat and grains are the major dietary sources. You get 35 to 75 mcg in a 3-ounce portion of fish, about 25 mcg in a 3-ounce portion of poultry or meat, and 15-35 mcg in 1 cup of pasta or rice or two slices of bread.
Vegetables and fruits generally supply only small amounts that add up as you eat more; one exception is the 18 to 36 mcg in a cup of cooked mushrooms. Also note that you can get the entire RDA in one Brazil nut.
While most everyone in the U.S. gets well over the RDA, it's important not to overdo it. The National Academy of Science warns that too much selenium can cause nerve damage, hair loss and digestive disturbances. To avoid potential problems, the maximum amount of selenium (from food and supplements) considered safe is 400 mcg - a level only likely to be reached with excessive fortified foods and supplements.
Q. Which cocktail is lower in calories, a martini or a margarita ?
A. Each of those drinks can be made in many variations that change the calorie load. A small martini might weigh in with about 120 calories - slightly lower than a margarita - but even a small addition like lime juice can brings calories closer to 160. In addition, some people make margaritas with sweet and sour mix and extra juice, or martinis with extra flavors (chocolate liqueur, for example), all of which add calories. And don't forget that alcohol in itself is a concentrated source of calories, so increased portions make calories increase quickly.
Although one standard drink is defined as 1 ounces of 80-proof liquor, many drinks contain double that amount or more. Just because it's served in one glass does not mean it's considered "one drink."
For weight control (and other health and safety concerns) be mindful of what and how much you drink, perhaps alternating alcohol with club soda or other low-calorie, nonalcoholic options.
• Karen Collins, registered dietitian, writes this column for the American Institute for Cancer Research. To submit a question, please write to Ask the Nutritionist, c/o the Daily Herald, 1759 R St., N. W., Washington, D.C. 20009. Questions will not be responded to personally.