November 29, 2007
Thursday AM

Fans of eating organic have always believed that organic fruits and vegetables packed a bigger nutritional punch than conventionally grown produce.

But until pretty recently, hard scientific evidence has been lacking.

Studies that seemed to prove the theory often turned out to be poorly designed -- the organic and conventional crops weren't grown in the same area or weren't the same variety, for example. Or the samples were too small, the studies too short or they were flawed in some other way, according to food chemist Alyson Mitchell, an associate professor in the Department of Food, Science and Technology at the University of California-Davis.

Mitchell says it was just a few years back that her own studies that found higher nutrient levels in organic crops were dismissed as nothing more than wishful thinking, no matter how well done the science was.

Now, though, the scientific fulcrum is swinging. It seems like a week doesn't go by without a headline from university researchers somewhere in the world who have shown that organic tomatoes, corn or some other fruits and vegetables contain more nutrients, especially when it comes to vitamin C and other antioxidants.

"There's definitely a trend," Mitchell says.

Just this year, three European studies have reported the benefits of organic crops, including peaches in France and apples in Poland.

The biggest was a four-year European Union-funded study of organic and conventional crops grown in side-by-side plots on 725 acres near Newcastle University, in the United Kingdom. The study showed levels of antioxidants 20 percent to 40 percent higher in organic wheat, tomatoes, potatoes, cabbage and lettuce, according to news reports.

Also making headlines was a 10-year study by a UC-Davis team led by Mitchell, which looked at dried tomato samples collected over 10 years from side-by-side organic and conventionally farmed plots just west of the university. The results, published in the Journal of Agricultural Food Chemistry, were dramatic: The organic tomatoes contained 79 percent more of one antioxidant, and 97 percent more of another.

Another UC-Davis study this year showed similar results for polyphenols (the antioxidants in red wine and blueberries), vitamin C (an important antioxidant) and some minerals in organically grown kiwi as compared with conventional fruit. Earlier research showed similar results for marionberries, strawberries and corn.

Mitchell says her team's review of studies since 2000 shows that research techniques have improved, and that the "better studies demonstrate a trend of higher levels of flavonoids (one type of antioxidant) and vitamins in fruits and vegetables."

Results seem to vary widely in the size of any organic benefit -- or whether there is a benefit at all. Mitchell's team spent three years looking at solids (a reflection of sugar) and antioxidants in fresh tomatoes and bell peppers. The organic tomatoes had higher levels of both solids and antioxidants than the conventional, but the bell peppers showed no differences, Mitchell said.

She's looking at spinach now, curious if a leaf will show the same results as a fruit.

The trend would seem to be great news for shoppers. It should mean that consumers are getting a nutritional bonus when they ante up the extra for organic, along with avoiding pesticides and contributing to a cleaner environment.

"No," says Mitchell. It's just not that simple.

You can't just figure you're getting more nutrients by buying organic tomatoes instead of conventional, she says.

Where the tomatoes were grown, what kind of tomatoes they are, how ripe they were when they were picked, if they were kept cool or not, and how long they've been in the store all affect nutrient levels.

"Variety is critically important," Mitchell says. Different varieties of tomatoes grown in the same area, in the same way, with the same handling and same amount of time on the shelf, will still vary in their nutrient levels simply based on their variety.

"The consumer doesn't have a clue, except for apples, what variety they're buying," Mitchell says. Yellow onions, for example, can be a dozen different varieties throughout the year.

UC-Davis scientists have done any number of "market basket" studies -- comparing store-bought fruits and vegetables -- and "they've all failed miserably," says Mitchell. "It's very depressing."

A two-year study of market broccoli will never be published, she says, because good research proved impossible. "How do you make a comparison when the conventional broccoli is on ice and the organic isn't?"

Processing adds another wrinkle. Mitchell's team studied 10 tomato-based pasta sauces, half organic, half not, and "we saw really no difference." If the organic tomatoes had more nutrients to start with, the extra had disappeared by the time they hit the jar.

"I think we're losing a lot of nutrition in processed foods," she says.

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