"When will you tell us the food value difference between frozen and canned and fresh fruits and vegetables?" asked the post card that arrived on my desk last week. Since the writer didn't include a name, phone number or address on the card, I'm responding here.
The answer varies with the type of fruit or vegetables, how they were handled or processed, which nutrients you're after and who you get your research from.
Around 1795, Napoleon offered 12,000 francs to anyone who could develop a method of preserving food as French soldiers suffered more casualties from malnutrition, scurvy and starvation than from battles. Nicolas Appert found success by packing food in bottles, corking them and submerging them in boiling water to stop spoilage. He was awarded the prize money by Napoleon himself, and canned goods have been an alternative to fresh food ever since.
Comparisons of canned and frozen versus fresh food are complicated, because "fresh" produce sometimes isn't that fresh. When it's been sitting around in warm temperatures, shipped and stored for a couple of weeks, or overcooked, it loses nutrients. Frozen fruits and vegetables, on the other hand, are usually canned or frozen right after harvest, when nutrient content is at its peak.
In 1998, the U.S. Food & Drug Administration granted the American Frozen Food Institute's petition to allow frozen produce to be labeled as "healthy." FDA stated that frozen fruits and vegetables are equivalent to fresh produce in regard to their nutrient profiles.
In 1995, the University of Illinois Department of Food Science analyzed a variety of canned, fresh and frozen fruits and vegetables. Although processing resulted in a small loss of nutrients, researcher Barbara Klein said "the effects are the same as what happens to a fresh vegetable when you cook it." (The study was conducted on behalf of the Steel Packaging Council, part of the canning industry.)
In 2000, University of Massachusetts nutrition professors did taste tests and a nutritional analysis of 13 "family-friendly" recipes and concluded that canned foods provided the same nutrition and taste as those made with fresh or frozen foods. The project was funded by a $200,000 grant from the Canned Food Alliance. Nutrition professor Kenneth W. Samonds compared protein, carbohydrates, vitamins and minerals in each dish.
Since this is a column and I can express my opinion, I personally can't help but be a little skeptical of studies funded by industry groups. I realize researchers have to get their money somewhere, but I just think there may be a chance for bias. (That's why I'm withholding judgment on Duke University's research this year praising high-protein, low-carb diets — it was paid for by the Atkins Foundation.)
"The Nutrition Bible," by Jean Anderson and Barbara Deskins, states that canned foods lose a little vitamin C and thiamin (vitamin B-1) in the heating process. If glass jars are used, the food also loses riboflavin (B-2,) a vitamin that succumbs to light. Fat-soluble vitamins A, D, E and K, and minerals and carbohydrates are fairly heat-stable, and protein levels also are not affected by canning. Another nutritional downside, according to the authors, is that most canned goods have added sugar or salt — although you can rinse much of it out with water.
Beta-carotene and lycopene, two antioxidant carotenoids that are thought to help prevent cancers, actually appear to be better absorbed by the body when the food has been cooked or canned. A report in the UC Berkeley Wellness Letter said that processing breaks down certain chemical bonds, and people eating cooked forms of these foods had higher blood levels of beta-carotene than those eating similar amounts of raw vegetables. Lycopene is found in tomatoes, so canned tomatoes and tomato sauce can be good choices.
An American Dietetics Association fact sheet states that canned vegetables and fruits generally supply a little less fiber than that found in fresh or frozen foods. Canned beans are the exception — they retain their high fiber content.
Since the nutrition label on canned and frozen foods lists the amounts of nutrients such as vitamins A and C, iron, calcium, fiber and protein, you can compare products when shopping.
In a perfect world, we would enjoy fresh-picked fruits and vegetables every day of the year. But most Americans don't get enough fruits and vegetables as it is. Canned and frozen foods are practical and convenient — they enable you to get dinner on the table quickly, to enjoy out-of-season blueberries at a reasonable cost, or to get the most of your salsa garden long after the frost settles. And if it comes down to opening a bag of chips or a can of peaches, it's pretty obvious which would win the nutritional nod.
E-MAIL: vphillips@desnews.com