RENEE MONTAGNE, host:
Now back to those flavonoids you mentioned, Robert. A farming experiment at the University of California Davis has found that organically grown tomatoes are richer in these particular kinds of antioxidants than conventionally grown tomatoes.
NPR's Allison Aubrey reports on one researcher who is determined to figure out exactly why that might be.
ALLISON AUBREY: Steve Kaffka stumbled upon organic gardening by accident. Back in the late 1960s, when he was a student at UC Santa Cruz, countercultural anti-war sentiments were high and there was word on campus that a bunch of students were digging out a brush covered hillside for a new organic garden.
Dr. STEVE KAFFKA (University of California-Davis): My girlfriend dragged me up there. I didn't want to go.
AUBREY: You weren't interested in farming?
Dr. KAFFKA: No.
AUBREY: But something clicked that day. Forty years later, a framed photo hanging on Kaffka's office wall at UC Davis shows him with a wheelbarrow at the center of the activity, running the show. He says he remembers that time well.
Dr. KAFFKA: Yeah. Well, I would've felt wonderful for doing the activity and overwhelmed because I was in charge and too young.
(Soundbite of laughter)
AUBREY: But it was a wonderful time?
Dr. KAFFKA: Yeah. You could do a thing that was both a craft and intellectually satisfying, and it was physical.
AUBREY: Kaffka went on to get a Ph.D. in agronomy. And one of his latest interests is to figure out if the way we grow things can actually make food more nutritious.
Dr. KAFFKA: Up here, we have two rows here. Probably be about 10,000 plants per acre.
AUBREY: On some fields just west of Davis, California, Kaffka and his colleagues have been comparing organic and conventional tomatoes grown in neighboring plots. They found that the organic ones have almost double the concentration of two types of flavonoids, which are considered to be healthy compounds with potent antioxidant activity. When we visited the site, a tractor was turning over last season's cover crop.
Dr. KAFFKA: Today's the day.
AUBREY: So it's a good time to be here, huh?
Dr. KAFFKA: Yeah.
AUBREY: Over the next few days, thousands of seedlings tomato plants will be transplanted here, and all of them need nitrogen to grow. Kaffka explains a key difference between organic and conventional is how the tomatoes are fertilized. With the conventional plots, Kaffka's team applies a commercial fertilizer.
Dr. KAFFKA: With fertilizer you can have as much available as you put on.
AUBREY: But with the organic plots, the nitrogen comes from manure and composted cover crops. These have to be broken down by the microbes in the soil before the nitrogen's released.
Dr. KAFFKA: When you use organic materials like this, it has to go through those breakdown processes. It takes time, and it's not all instantaneously available.
AUBREY: So it's a slower feed.
Dr. KAFFKA: Yes.
AUBREY: With less nitrogen, the organic tomatoes may have more time to do things other than just grow, such as to make flavonoids. Kaffka's theory is that the difference in how the plants are fertilized may explain why the organic tomatoes over a ten year period contained 97 percent more kaempferol and 79 percent more quercetin. These are two common flavonoids.
It makes for a very interesting finding, especially for those who assume that organic is healthier. But Kaffka says it's not so clear cut.
Dr. KAFFKA: There are a lot of things when you do these comparisons that could confound the results.
AUBREY: The soil types could be different, moisture or irrigation may vary from plot to plot, and the variety of tomatoes grown could change the picture.
Dr. KAFFKA: Just calling something conventional or organic doesn't tell you that.
AUBREY: Kaffka says what he's trying to do is pinpoint cause and effect. If limiting the supply of nitrogen to tomatoes could consistently lead to more flavonoids, then perhaps conventional farmers could do this too. But there's much more work to do to test this theory.
Kaffka's personal views on eating well haven't changed much since he became a researcher. The scientist in him remains skeptical that organic food on the whole is any healthier, but the foodie in him loves to eat here.
Dr. KAFFKA: This is a combination of a food coop and a food kind of culture place.
AUBREY: At the David coop, he cruises past stinky cheeses, specialty meats, and rows of bright-colored produce.
Dr. KAFFKA: Purple, everything's purple, purple asparagus.
AUBREY: And you eat it all?
(Soundbite of laughter)
Dr. KAFFKA: Yeah.
AUBREY: And love it all?
Dr. KAFFKA: Yeah, sure.
AUBREY: Kaffka says he's got friends who farm organically and he likes buying their food to support their way of life.
Dr. KAFFKA: I think acting in ways that you find consistent with some good principle, how can that be bad?
AUBREY: But he says the research is important too. It can save us from our biases and help tease apart the consequences of different ways of growing food.
Allison Aubrey, NPR News.
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MONTAGNE: And did you know the label 100 percent natural has different meanings for cookies and, say, chicken fingers? Or that those cage-free chickens might not ever have seen the outdoors? You can find out how to decipher food labels at npr.org/yourhealth.