DEAR DR. BLONZ: Is there more vitamin A in dark-colored vegetables than lighter-colored vegetables? There is a debate in our class. -- M.H., San Jose, Calif.
DEAR M.H.: There is no pre-formed vitamin A in fruits and vegetables; rather, plant foods have compounds that the human body can convert to vitamin A as needed. The key players are the carotenoids, a group of colorful compounds that range from yellow to deep red. Any food's vitamin A potential depends on the carotenoid present, as not all can end up as vitamin A. For example, lycopene (red), lutein and zeaxanthin (yellow-orange) do not get changed into vitamin A.
Let's look at a group of vegetables to see how much vitamin A they provide per serving, first on a weight basis (vitamin A per unit weight), then on a calorie basis (vitamin A per calorie). Our eight representatives are all examples of healthful foods and excellent dietary sources of carotenoids. They are: fresh spinach, basil, kale, carrots, and leaf lettuce; baked sweet potato; canned pumpkin; and dried pasilla peppers.
Taking portions of identical weights, they rate, from highest to lowest: dried pasilla peppers, sweet potato, carrot, pumpkin, kale, spinach, lettuce, basil.
Viewing this same list on vitamin A per calorie, the highest to lowest are: lettuce, pumpkin, carrots, spinach, kale, sweet potato, basil, dried pasilla peppers.
In both cases, there is a slight straying from any conclusion that dark equals more vitamin A. Perhaps the issue is that your discussion was limited to one known nutrient. Eating foods rich in natural colors is a great goal, and their presence tends to signify a richness of natural, healthful phytochemical compounds.
You can get additional information on the nutrient content of foods by visiting the USDA database at ndb.nal.usda.gov.
DEAR DR. BLONZ: I just read an article about potatoes, and I am a bit concerned. I just bought a bag of organic Russet potatoes, and they sprouted very quickly. I have been pulling the sprouts off, and the potatoes don't appear terribly green. Are these still harmful to consume? I would not prefer to waste five pounds of organic potatoes! -- K.S., via email
DEAR K.S.: You might consider returning them, especially considering that you "just" bought them. But if there is no green on the potatoes, and they are still firm, you can remove the sprouts and a bit of the sprout base and it should be fine. One issue with the alkaloids present in green potatoes (solanine) is the dose, so as long as they are only for a side dish, there should be no problem. Potatoes should be stored in a cool, dark place and you shouldn't get more than you would expect to eat in a week or so. One issue is that you don't know how long the potatoes were at the store before you bought them. Always give produce a good inspection before you put it into your cart.
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.