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Ask the Bridge
Are fresh vegetables the most healthful to eat?
Actually, in terms of nutritional value, the benefits of fresh vegetables over frozen or canned are not necessarily significant, says Roberta Durschlag, a SAR clinical assistant professor of nutrition. That’s because it can take up to two weeks for fresh vegetables to reach the supermarket, during which time they lose some nutritional value.
“On the other hand, while vegetables used for freezing and canning are processed shortly after harvest,” she says, “they are subjected to heat treatment during processing, which also reduces the level of many nutrients.”
Regardless of whether vegetables are fresh, frozen, or canned, their nutritional value is affected by how they are stored and prepared in the home — exposure to water, oxygen, light, and heat, for instance, decreases nutrient content, Durschlag says.
Therefore, vegetables should be stored away from light and heat, cut into large pieces during preparation to limit the surface area exposed to water, oxygen, heat, and light, and cut and cooked as close as possible to the time they will be served. Furthermore, vegetables should not be soaked before cooking, as many of the nutrients are water-soluble and will leach into the water.
“Cooking methods that reduce the amount of water the food is exposed to as well as reduce the cooking time and temperature are preferred,” says Durschlag. “Baking and grilling vegetables tend to minimize nutrient losses because they involve no addition of water. Similarly, frying vegetables or ‘panning’ vegetables, where the food is cooked briefly in fat in an open pan and then covered to complete the cooking, lead to reduced nutrient losses.”
Boiling can cause significant nutrient losses, but these can be minimized “by leaving the skin on vegetables, decreasing the quantity of water used, cooking vegetables until just tender, and covering the pot to reduce cooking time,” Durschlag says. “Steaming vegetables eliminates the contact between the food and water and thus leads to nutrient retention. Microwave cooking should be done in the smallest amount of water necessary to reduce leaching of nutrients into the water. Since some loss of nutrients is inevitable with any cooking method, consumption of some raw vegetables is desirable.
“While it is recommended that people consume three to five servings of vegetables daily, only 45 percent of Americans are eating the minimum three servings each day, and one of these servings is white potatoes,” she continues, pointing out that a serving of vegetables consists of half a cup of cooked or raw chopped vegetables, one cup of raw leafy vegetables, or three-quarters of a cup of vegetable juice. “The most significant challenge therefore is to get Americans to consume the proper quantity of a variety of vegetables whether they be fresh, frozen or canned.”
“Ask the Bridge” welcomes readers’ questions. E-mail bridge@bu.edu or write to “Ask the Bridge,” 10 Lenox St., Brookline, MA 02446.
3
September 2004
Boston University
Office of University Relations