By Barbara Day, M.S., R.D., C.N.
The 2005 U.S. Dietary Guidelines, the American Heart Association and the American Cancer Institute agree on one important health strategy — Americans need to eat more fruits and vegetables, at least 4 ½ cups per day.
However, research has determined that this health strategy is not being followed most Americans.
Fruits and vegetables are known to be rich in disease-fighting antioxidants and high in vitamins, minerals and fiber, too. These superstar foods help to lower blood pressure, control weight, lower risk of several types of cancer, lower the risk of heart disease and stroke plus reduce the risk of type 2 diabetes.
In the past, “common perceptions include the notion that fresh is always best,” says Christina M. Bruhn, Ph.D. Bruhn and her team of investigators from the Department of Food Science and Technology, University of California–Davis, published a recent study in the Journal of Food Science and Agriculture which concluded all forms of fruits and vegetables — canned, fresh and frozen — can provide nutrients needed to maintain health ( www.mealtime.org ).
Bruhn said “this study shows us, however, that eating a variety of fruits and vegetables in all forms is important to a healthy diet.” Bruhn's team suggested that getting the most bang for your buck from fruits and vegetables is important, but how these foods are handled during storage and how they are cooked determined how many nutrients are available to be utilized by our bodies.
Eating fresh fruits and vegetables as soon as possible to preserve the nutrients in the food is the best strategy. Loss of nutrients in fresh products can be up to half of its original nutrient content prior to consumption if improperly stored and the overcooked. For example, fresh vegetables, such as spinach and green beans, lose up to 75 percent of their Vitamin C within seven days of harvest, even when held at the recommended refrigerator temperature. Vitamin C, a water-soluble nutrient, is sensitive to heat, light and oxygen.
Depending on the food, freezing and canning may actually preserve nutrient content. Most frozen and canned foods are processed within hours of harvest. The initial thermal treatment of canned products can result in a loss of nutrients, but nutrients are relatively stable during storage due to lack of oxygen. However, cooking the canned foods improperly can cause further losses as well. If you quick heat the vegetable and eat it versus cooking the vegetables over heat can result in a greater loss of nutrients. Canned foods are actually recipe ready.
Frozen products lose fewer nutrients initially because of the quick-cook blanching process, but they lose more nutrients during storage due to oxidation. Vitamin C is lost when frozen vegetables are blanched, but some fruits have ascorbic acid added to prevent browning, so the Vitamin C content may actually be higher. It has been reported between 10-90 percent of Vitamin C is lost during the canning process but the nutrient does not change significantly during storage of canned products.
B vitamins, thiamin, B6 and riboflavin are sensitive to heat and light so these nutrients would be lost during the canning process. In addition, because these nutrients are water-soluble, 20–60 percent of the nutrients are lost during the blanching process prior to freezing.
The good news is that mineral and fiber content are similar in fresh, canned and frozen fruits and vegetables. The fiber content is lower in canned or fresh fruits and vegetables if the skin is eliminated, such as in apples versus applesauce.
Fat-soluble nutrients such as vitamins A, E and carotenoids, including lycopene, are sensitive to heat, light and oxygen but because they are fat soluble, little is lost in the blanching process in frozen foods. In fact, research has determined that for some nutrients, like lycopene, canned products, such as canned tomatoes and tomato paste, are higher in lycopene than in fresh tomatoes.
By the time some fresh foods are consumed — canned, fresh, or frozen may be nutritionally similar. For example, if you purchase fresh corn and it sits in the refrigerator for a week or so and then you overcook it, throw the water out – it's likely to contain less nutrients that frozen or canned corn. When cooking vegetables in a large amount of water, some of the nutrients are being leached out of the food and these nutrients get thrown out with the water.
That's one reason I like to cook soups and stews for my family. You can add vegetables — fresh, frozen or canned to a crock-pot, cook the food over time and eat the soupy fluid, which is nutrient packed. You don't throw the nutrients out with the water.
The Take Home Message is canned, frozen and fresh fruits and vegetables can contribute nutrients to your diet. Don't disregard canned or frozen fruits and vegetables as a source of nutrients — especially if you can always afford to buy fresh.
Note: For kid-friendly recipes that adults will love to eat, too, check out the Cooking on the Go column.
