In trying to discover whether organic food is better, I think the first thing to recognise is that only careful and systematic research can answer this.
Some people believe that natural = good, so anything that has been treated with 'chemicals' must necessarily be worse. But this is based more on emotion and cultural values than evidence. For example, it might make no more sense to worry about pesticides than to worry because water has been chemically treated to kill bacteria, and runs through copper pipes. We just can't tell without decent evidence.
Decent evidence has to be more than anecdotal. It's no good saying, 'John felt much better when he started eating organic carrots.' Evidence has to come from research that eliminates problems such as placebo effects, demand characteristics, reconstructive memory, uncontrolled variables and so on. So: high quality research from people who know what they're doing.
And 'a study found that...' is little help either. A key feature of knowledge is replication. Science operates on a balance of evidence, and that takes a lot of studies, carried out by a lot of people, over a period of time.
So what have the reviews of research got to say about organic food? There have been a number of meta-analyses over the years. To my knowledge, they all say the same thing: there's very little evidence that organic food is any healthier.
For example, there was a big one last year:
After analyzing the data, the researchers found little significant difference in health benefits between organic and conventional foods. No consistent differences were seen in the vitamin content of organic products, and only one nutrient — phosphorus — was significantly higher in organic versus conventionally grown produce (and the researchers note that because few people have phosphorous deficiency, this has little clinical significance). There was also no difference in protein or fat content between organic and conventional milk, though evidence from a limited number of studies suggested that organic milk may contain significantly higher levels of omega-3 fatty acids.
The researchers were also unable to identify specific fruits and vegetables for which organic appeared the consistently healthier choice, despite running what Bravata called “tons of analyses.”
“Some believe that organic food is always healthier and more nutritious,” said Smith-Spangler, who is also an instructor of medicine at the School of Medicine. “We were a little surprised that we didn’t find that.”
Pesticide levels are lower in people who eat organic food, but there's no evidence as yet that this has any significance. It's worth bearing in mind that a lot of people worried about 'chemicals' in food are exposing themselves to a huge array of 'chemicals' - and in massively higher concentrations - when they wash their hair and deodourise.
Here's the link for the report on the meta-analysis: Little evidence of health benefits from organic foods, Stanford study finds - Office of Communications & Public Affairs - Stanford University School of Medicine