A farming experiment at the University of California, Davis, has found that organically grown tomatoes are richer in certain kinds of flavonoids than conventionally grown tomatoes. And one researcher is curious to determine why this may be.
Stephen Kaffka cut his teeth in organic gardening when he was a student at the University of California, Santa Cruz, in the late 1960s. He was involved in running the now-renowned student garden there, a task that was both intellectually satisfying and physically challenging. "It was a great time," he recalls.
Kaffka went on to get a Ph.D. in agronomy. Now, one of his latest interests has taken him back to his organic roots — a desire to figure out if the way we grow things can actually make food more nutritious.
In Northern California, on some fields west of Davis, Kaffka and his colleagues have been comparing organic and conventional tomatoes grown in neighboring plots. It's part of a UC Davis study dubbed the "Long-Term Research on Farming Systems Project," which was begun in 1991 and is slated to last 100 years.
So far, the researchers have found that the organic tomatoes have almost double the concentration of two types of flavonoids — quercetin and kaempferol — which are considered to be healthful plant compounds with potent antioxidant activity. The 10-year mean levels of quercetin were 79 percent higher than those in conventional tomatoes, and levels of kaempferol were 97 percent higher.
The Answer in the Dirt
The increased flavonoid levels, Kaffka suspects, could stem from the difference in how organic and conventional tomatoes are fertilized.
On Kaffka's plot, the conventionally grown tomatoes get commercial fertilizer made with soluble inorganic nitrogen, a form of nitrogen the plants can take up very quickly. The organic tomatoes get nitrogen from manure and composted cover crops. These organic materials have to be broken down by the microbes in the soil before the nitrogen is released to the plants.
"It takes time," Kaffka says, and the nitrogen is "not instantaneously available."
With limited nitrogen, the organic plants may grow slower, says Alyson Mitchell, a food chemist at UC Davis. When this happens, she says, the plant "has more time to allocate its resources toward making secondary plant metabolites" such as flavonoids.
Though such findings are intriguing to researchers, Kaffka cautions that there are many factors that could confound the results: The soil types could be different, moisture or irrigation might have varied from plot to plot, and the variety of tomatoes might have played a role.
He points out that the few rigorous studies that have compared organic systems with conventional systems have returned mixed results. There is no consistent evidence to suggest that organic methods lead to more healthful foods. So Kaffka remains skeptical.
Because growing systems are so complicated, Kaffka says he needs additional research to pinpoint a cause and effect between fertilization and flavonoids. If future research confirms that limiting the supply of nitrogen to tomatoes consistently leads to more flavonoids, then perhaps conventional farmers could use this approach, as well.
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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.
(Soundbite of music)
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. Transcript provided by NPR, Copyright NPR.