In our talks to community groups, our audiences are almost always surprised by our observation that there is very little scientific evidence showing that organically-grown food is healthier than conventionally-produced food. There is some highly debated evidence that organic vegetables and fruits may have more nutritional value, such as higher Vitamin C, but the truth of the matter is that the type of food you're eating will have much more effect on nutritional quality than whether it was grown organically. For example, a Golden Delicious apple is going to have less vitamin C than almost any other type of apple you can ingest. And there is no real evidence that organic meat or milk are any better for you than conventionally produced. Similarly, organic food from the farmer's market may taste better than food from the grocery store, but that's because of the freshness, not the production method. Our audiences are surprised by these results because a) they want organic to be healthier ("Why am I paying more for this if it's not healthier?"), and b) we assume something produced in a more "natural" way would be healthier.
But organic describes a production method. For fruits and vegetables, for example, organic growers use a variety of techniques to introduce nutrients (primarily nitrogen) into the soil and keep critters from devouring the plant, thus eliminating the need to apply synthetic fertilizers and pesticides. Unfortunately, organic growers still use organic pesticides which may be just as damaging to people and the environment as synthetic pesticides. For animals, organic methods involve providing access to organically-grown feed and pasture and avoiding antibiotics and growth hormones. The bottom line is, however, that these methods have little to do with the internal chemical composition of the plant or animal, which is where the nutritional value of the food comes from. Most pesticides, after all, are applied to the exterior of the plant to deter insects and rodents from eating it, and are (supposed to be) washed off the fruit before we eat it.
Does the lack of scientific documentation for the health benefits of organics mean you are wasting your money and should quite buying them? No, for a couple of reasons. First, in many ways, scientific research into organic farming is closer to its beginning than its final definitive conclusions. Congress, for example, just started providing funding for organic research in 2007. (Funding was not provided in the Organic Food Production Act of 1990 because members of Congress on the Agriculture committees, who have traditionally had close ties with conventional farmers, did not want to suggest that there was anything "wrong" with conventional agriculture.) Buying organic sends a signal to farmers that you will make it worth their while economically to cut back on their uses of chemicals. Buying organic is a value statement about the "right" way we want our food to be produced.