& Alan Titchenal Monday, January 18, 2010
The dark side of healthful 'superfoods'
Which is more important, eating healthful foods or consuming a healthful diet?
We often see popular articles with titles like: "The Top 10 Most Healthful Superfoods." It would be great if we could guarantee good health just by eating only these "health foods."
But for virtually every "health food," there are potential problems along with more commonly extolled virtues. Here are some foods frequently recommended as healthful superfoods:
Beans are a great source of carbohydrate, protein and dietary fiber and contain some essential vitamins and minerals. However, beans also are high in compounds that impair the absorption of minerals like iron and zinc. Over time, a diet too high in beans could increase the risk of mineral deficiencies.
Brazil nuts are an excellent source of selenium. Many of us don’t get enough of this important mineral in our diets. However, the Institute of Medicine has set an upper safe limit for daily selenium intake that is easy to exceed if you eat too many Brazil nuts every day. The selenium upper limit for adults of 400 micrograms per day can be exceeded with just five Brazil nuts that contain over 500 micrograms. Selenium toxicity can lead to fingernail brittleness, hair loss, intestinal disturbances, skin rash, fatigue, irritability, and nervous system problems.
Olive oil provides a variety of beneficial components that may be lacking in other oils. However, olive oil is quite low in the two key essential fatty acids, the most important components of dietary fat. To meet the recommended adequate daily intake of these fatty acids requires about 2,000 calories of olive oil.
Spinach is another healthful food mainly due to a variety of health-promoting phytochemicals. However, spinach often is incorrectly promoted as a good source of calcium and iron. Unfortunately, other components of spinach prevent the absorption of most of these minerals. Also, due to high levels of oxalic acid, too much spinach could increase the production of kidney stones for some.
Almonds, like other nuts, can be a healthful component of the diet. Like all nuts, however, they are rich in calories, so moderation is the key.
Green tea is widely extolled for its beneficial content of polyphenols that are linked to reduced chronic disease risks. However, when consumed with other foods, these polyphenols reduce the absorption of important trace minerals. Too much tea (green or black) also can potentially supply excessive amounts of aluminum, fluoride, and can interfere with the function of a number of medications.
Choosing wholesome foods is important for good nutrition. But remember: "Moderation in all things, even "superfoods."
Joannie Dobbs, PhD, CNS and Alan Titchenal, PhD, CNS
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa.
Dr. Dobbs also works with the University Health Service
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