Not long ago, ripe organic tomatoes were for sale at my market for $3.99 a pound. Across the aisle, nearly identical looking tomatoes were going for $2.79. Like most shoppers in these belt-tightening times, I found myself pondering the question: When it comes to nutrition, is organic really worth the higher price?

Isn’t a tomato a tomato, no matter how it’s grown?
Maybe not. How produce is grown—organically versus conventionally—can influence its nutrients, recent research suggests. For some fruits and vegetables, organic may have a distinct nutritional edge.

The most impressive findings come from a unique experiment underway at the University of California at Davis. In 1993, food scientists set aside a patchwork quilt of ten adjacent fields in the heart of California’s fertile Sacramento valley to compare farming methods, including organic and conventional. Although previous comparisons have been done around the world, many used fruit or vegetables from widely separated fields, grown under different weather and soil conditions.

“That’s like comparing apples and oranges,” UC Davis plant physiologist Adel Kader, PhD, told me. Different growing conditions can have a significant impact on nutritional content of produce. To create a level playing field, the UC Davis Long-term Research on Agricultural Systems project compares produce grown in adjacent fields with the same basic soil and the same climate.

The latest findings give champions of organic produce something to cheer about. Analyzing tomatoes grown over the past ten years in the test plot, UC Davis food chemist Alyson Mitchell, PhD, and her colleagues found that organically-grown tomatoes have consistently higher levels of vitamin C and other antioxidants, including flavonoids, which are naturally-occurring compounds in fruit and vegetables linked to lower heart disease and cancer risk. Organic tomatoes had 97 percent higher levels of a flavonoid called kaempferol, and 79 percent higher levels of another, called quercetin.

Because Mitchell’s results combine ten years of measurements, they are considered more reliable than single-year comparisons. And they match other findings. In 2003, Mitchell’s team found higher levels of key nutrients in organically grown corn, marionberries, and strawberries. Another UC Davis team, led by Kader, reported that organic kiwis have more flavonoids, as well as more vitamin C, than their conventional counterparts.

Related findings suggest that potatoes grown organically also have a nutritional edge. So do organic grapefruit, according to a 2007 study by experts at the USDA’s Agriculture Research Service in Weslaco, Texas, who compared Rio Red grapefruits from adjacent fields. The nutritional advantage makes sense, Gene Lester, PhD, the plant physiologist who led the USDA study, explained. “Plants produce antioxidants and other phytochemicals to protect themselves from insect infestations. Plants grown organically have to work harder to fend off pests.”

How crops are fertilized can also affect nutrient content. In conventional farming, growers apply nitrogen directly, which causes plants to grow rapidly. Organic farming, on the other hand, uses manure and compost for fertilizer, which results in slower growth. That favors the development of what plant biologists call secondary metabolites, the substances that make carrots orange and tomatoes red and also account for flavor and nutrient content.

But not all crops seem to be equally affected by growing method. Another UC Davis study found no difference between organic and conventional bell pepper, for instance. Wheat grown conventionally appears to be just as nutritious as the organic version. Different crop plants have their own unique complement of defensive compounds, which may explain why some respond more to differences in their environment.

Keep in mind: the nutritional advantage of some organically grown crops is often slight. And freshness may be even more important. Spinach grown organically may start out with higher levels of some nutrients, Alyson Mitchell explained, but after being stored overnight and then carted a hundred miles in an open truck on a hot day, it may end up having lower levels than conventionally grown spinach frozen soon after being harvested.

Nutrition aside, there are other reasons to favor organic produce, of course. Organics are less likely than conventional produce to have pesticide residues. Workers on organic farms are less likely to be exposed to chemicals. Organic farming creates results in healthier, more fertile soil, promoting sustainable agriculture.

All of that’s crucially important. But if the price of organic produce is beyond your budget, buy conventional. Most of us would be a lot healthier if we ate more fruits and vegetables, no matter how they’re grown.

Tags: fresh food, nutrition, organic farm, organic produce, organic vs. conventional