Are Organic Tomatoes Better? A farming experiment at the University of California, Davis, has found that organically grown tomatoes are richer in certain antioxidants than conventionally grown tomatoes. One researcher is on a quest to figure out why.

Are Organic Tomatoes Better?

Are Organic Tomatoes Better?

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Tomato on a vine

Is "natural" the same as "organic"? What about "100 percent organic"? Here's a guide to deciphering food labels: what's meaningful, what's dubious, and what's total fluff.

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.

Antioxidant Amplification

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.

Unanswered Questions

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.

Navigating Food Labels

Did you know the label "100 Percent Natural" has different meanings for chicken fingers, cookies and various other foods? Or that those "cage-free" chickens might not ever have seen the outdoors? Here's a guide to help sort out what's meaningful, what's dubious — and what's total fluff.


This is the gold standard among food-labeling terms. The National Organic Program is administered by the U.S. Department of Agriculture, and it permits the official organic seal only on products that meet strict requirements. In the United States, any manufacturer or marketer's claims of "organic" must be certified by an accredited third party.

* Crops — Certified organic crops generally cannot be produced using synthetic fertilizers, pesticides or genetically modified organisms, though some synthetic chemicals are allowed if they cannot be produced naturally and are not harmful.

* Livestock — Certified organic meat, milk and egg products must come from livestock raised without antibiotics or hormones. The livestock also must be fed organic food, not be genetically modified and be allowed access to outdoors. Products from animals that become sick and are given antibiotics cannot be considered organic.

* Other Food Products — There are different levels of organic labels:

  • 100% Organic: Contains only organically produced ingredients (excluding water and salt). Can display the USDA organic seal.
  • Organic: Contains 95 percent or more organically produced ingredients by weight or volume (excluding water and salt); all other ingredients must be on USDA's approved list. Can display the USDA seal.
  • Made with Organic Ingredients: Contains 70% or more organically produced ingredients. Cannot display the USDA seal.


For meat and poultry, the "natural" label applies to how meat is processed — not how animals are raised. The USDA defines it to mean that meat and poultry must be only "minimally processed" and cannot contain any artificial flavoring, color ingredients, chemical preservatives or artificial ingredients.

Producers sometimes use the label to reflect that animals did not receive antibiotics or hormones. But this falls outside the USDA's definition and can vary by producer. If you want to know specifics about how animals were raised, cattle specialist Mike Baker at Cornell University says many producers spell out their guidelines on their Web sites. Such claims generally have not been verified by a third party, however.

In all other instances, "natural" is a largely meaningless labeling term. The USDA defines it only in regard to meat and poultry, so what it means on granola bars is anyone's guess.

Farmers who choose to use the label "Certified Naturally Grown" are required to conform to national organic standards, but use of the label is governed by a nonprofit rather than a governmental program. These claims are certified by other farmers rather than the USDA. This alternative may be one instance in which buying "natural" foods is a good bet.


"Sustainable" implies that farms are managed to benefit natural resources and the local economy, says Dr. Anu Rangarajan, director of Cornell University's Small Farms Program. But no government agency or official third party verifies the claim. Some independent groups — including the World Wildlife Fund and Core Values — have created sustainability standards and their seals may be displayed on products that meet these guidelines. Companies such as Unilever also have created an internally imposed standard for "sustainable" products. Consumers should look for a label that tells who is verifying the claim.

No Hormones Administered

"Hormone-free" is misleading, as all animal products naturally contain hormones. The USDA allows the label "no hormones administered" on meat or poultry products to designate that the animals did not receive added hormones during their lifetimes. The USDA already prohibits the use of hormones in pigs and chickens, so a "no hormones administered" label on pork or poultry doesn't mean the producer took special measures. On other meat, the manufacturer or marketer applies this term; it is not independently verified.

No Antibiotics Administered

The USDA doesn't approve the term "antibiotic-free" but does allow "no antibiotics administered" or "raised without antibiotics," which mean that an animal did not receive any antibiotics during the course of its lifetime. The claim is not independently verified.

Free Range

The USDA defines this to mean birds are allowed access to the outdoors for more than half their lives. However, just because the cage door was open doesn't mean the birds actually spent time outside. This claim is not independently verified.


Both "cage-free" and "free roaming" are defined by the USDA to mean that birds can roam indoors, and don't guarantee that birds are allowed access to the outdoors. This claim is not independently verified.


Grass-fed animals produce meat that is higher in vitamins and omega-3 fatty acids and lower in fat than grain-fed animals. According to the USDA, the label means the animal consumed only grass or forage throughout its adult life, was fed no grain and had continuous access to pasture during the growing season. This claim is not independently verified.

Omega-3 Enhanced

In eggs, this USDA term means that the laying hens were fed a diet enriched with natural sources of omega-3 fatty acids, such as flaxseed. The FDA requires that the quantity of omega-3s per egg also be displayed on the label. But the amount of omega-3s can vary greatly among eggs and, in some cases, might not be much more than the amount in a conventional egg (about 37 mg, according to the USDA's Nutrient Database).