DEAR DR. BLONZ: A friend told me to take guarana pills for alertness, better concentration and faster learning. I've also heard that guarana is used as a cure for impotence. What can you tell me about it? -- D.P., Charlotte, North Carolina
DEAR D.P.: Guarana (Paullinia cupana) comes from the seeds of a South American climbing shrub. The claimed effects you mention, at least those associated with alertness and better concentration, relate to the fact that guarana has a high concentration of caffeine -- over twice that found in the coffee bean, the kola nut or cacao (cocoa). Coffee drinkers view their brew with a degree of reverence for its stimulating effects, but caffeine actually functions as a plant's phytochemical defense to dissuade animals from dining on its seeds.
As regards your statement concerning the other alleged use for guarana, there is no research to support the use of guarana or caffeine to treat impotence.
DEAR DR. BLONZ: I know this is the case with bananas, but do oranges get sweeter and improve in nutritional value as they age? What about color and storage? -- B.B., Baton Rouge, Louisiana
DEAR B.B.: There is no reason to "save" an orange in the hopes that it will improve in flavor or nutritional value. Some fruits, such as bananas or stone fruits, contain enzymes that remain active after harvest, and these enzymes break down complex carbohydrates into simpler, sweeter-tasting sugars. This, however, isn't the case with oranges, a fruit that is traditionally harvested at the peak of ripeness.
What that means is that when it is picked, the orange is as sweet as it's going to be. It is also the time at which the vitamin C content will be the highest. As for color, it may not always be a reliable indicator of ripeness and flavor, as perfectly ripe oranges sometimes carry a greenish tinge. The color of an orange tends to reflect the temperatures in the days prior to harvest.
Although they will keep for a few days at room temperature, it's best to keep oranges in the refrigerator. When an orange begins to shrivel, its nutrient value will have also begun to decline.
DEAR DR. BLONZ: I am hoping that you can weigh in on a debate my son and I are having. I told him that when vegetables are boiled, nutrients evaporate with the steam unless the lid is on. He has dismissed this, saying that all the nutrients stay in the cooking water. -- J.A., San Diego
DEAR J.A.: Your son is much closer to the truth. Although some nutrients are destroyed by heat, they do not evaporate and get carried away in the steam. Those nutrients that are water-soluble and heat-stable will remain intact in the cooking water. The nutrients that don't dissolve in water remain in the vegetable.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.