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March 16, 2007 -- Think fresh fruits and vegetables are always the most nutritious? Think again.
If you can't grow your own produce and eat it within hours of harvesting, canned and frozen fruits and vegetables can be every bit as good for you as fresh ones, and in some cases even better.
That is the finding from a newly published review of the research, commissioned by the canned- food industry.
The review comes just one day after the CDC reported that fewer than a third of adults in the U.S. eat the recommended amount of fruits and vegetables.
"There is an idea among consumers that if it isn't fresh, it doesn't count," Christine M. Bruhn, PhD, tells WebMD. Bruhn is a co-author of the study and director of the Center for Consumer Research at the University of California-Davis.
"People need to be encouraged to eat more fruits and vegetables, whether they be fresh, frozen, or canned -- whatever form best fits their lifestyle and their pocketbook."
The U.S. government recommends that adults eat at least five servings of fruits and vegetables a day, including two or more servings of fruits and three or more servings of vegetables.
Bruhn says processed fruits and vegetables can help more Americans reach this goal.
Her review highlighted cases in which canned or frozen vegetables seem to be nutritionally superior to fresh, including the case of tomatoes and lycopene.
Lycopene is a carotenoid pigment found in tomatoes, believed to be protective against heart disease and even some cancers.
Fresh tomatoes have less available lycopene than canned tomatoes or tomato sauce.
According to one study included in the review, tomato paste has more than six times the lycopene of fresh tomatoes.
Another study from the late 1990s suggested that vegetables such as green beans and spinach lose about 75% of their vitamin C after being stored in the refrigerator for a week.
The research suggested that the canned or frozen versions of these vegetables may be more nutritious than their fresh counterparts that have been stored for many days, says Bruhn.
"People are probably not aware that some nutrients, like vitamin C, are actually quite susceptible to exposure to air," she says.
The American Dietetic Association weighed in on the fresh versus canned debate in a statement released in January of 2006, noting that "canned fruits and vegetables are good substitutes for fresh produce and sometimes may be healthier."
"Fresh produce is nutritionally better when it is used within a few days of picking," the statement read. "Canned produce is picked and canned at its peak, so even though the heating process destroys some vitamins, the majority of the nutrients remain."
The statement further noted that canned tomatoes, corn, and carrot products provide higher amounts of some (antioxidant) phytochemicals than their fresh counterparts as a result of the canning process.
The ADA recommended choosing canned products with little added salt or sugar.
Tufts University nutritionist Alice Lichtenstein, ScD, tells WebMD that while most canned vegetables are loaded with salt, salt-free versions are usually also available.
"You can also rinse your canned vegetables off, and choose fruits packed in their own juice," she says.
Lichtenstein points out that canned and frozen fruits and vegetables give people the opportunity to eat a variety of healthy produce year-round.
"The quality and variety of frozen fruits, especially, has really improved in recent years," she says. "These products can be very good, the cost is often better than fresh, and you don't have to worry about seasonal availability and spoilage."