A recent review of 240 studies has concluded that:
The published literature lacks strong evidence that organic foods are significantly more nutritious than conventional foods. Consumption of organic foods may reduce exposure to pesticide residues and antibiotic-resistant bacteria.
Organic produce has become increasingly popular in recent years. There are several reasons that consumers might prefer organic produce, including the belief that organic farming is better for the environment and more sustainable. I am going to focus in this article about the health effects of organic produce. Environmental claims for organic farming are complex and controversial – I will just say that such claims largely fall prey to the naturalistic and false dichotomy fallacies. In my opinion, farming practices should be evaluated on their own merits individually, based on evidence rather than philosophy. Sustainable and environmentally friendly farming are certainly laudable goals and I support farming practices promote them, however they are labeled.
The alleged superiority of organically grown produce is a separate question. In a 2003 survey 68.9% of people who purchase organic food said they did so because they believed it to be healthier (more than any other reason given). However, fifty years of research has so far not produced convincing evidence that there is any health benefit to consuming organic food. Likewise, systematic reviews of nutritional quality of organic produce also reveals no difference from conventional produce.
The recent review is therefore in agreement with previous reviews – organic produce is not more nutritious or healthful, but it is more expensive.
Some studies that find small differences in the content of specific nutrients may be due to confounding factors. For example, organic produce is generally smaller than conventional produce, so if nutrient content is measured by mass (as opposed to the total for an individual vegetable or piece of fruit) organic produce may have a slightly higher concentration. This does not necessarily translate to more overall nutrients for the consumer. Further, many studies measure multiple endpoints (nutrients) and find some differences, but may not be properly accounting for multiple analyses. The researchers in the recent study found that results were “heterogeneous” – meaning that there were significant differences in outcome among the studies. This could indicate a lack of replicability of specific outcomes, indicating that differences were more artifacts of method rather than genuine.
One type of study that I have not seen is essentially the equivalent of an “intention to treat” analysis – what is the impact of buying organic food in the real world. Even if there are tiny nutritional advantages to organic food (although to be clear this conclusion is not supported by the evidence), is there an overall nutritional advantage to eating organic? Does the higher price mean that for many consumers fewer overall fresh produce will be consumed?
The recent review did find that organic produce had fewer pesticide residues than conventional farming. However, there is no evidence that these low levels of pesticides present any health risk. The review found:
The risk for contamination with detectable pesticide residues was lower among organic than conventional produce (risk difference, 30% [CI, −37% to −23%]), but differences in risk for exceeding maximum allowed limits were small.
So while there was a difference, this did not result in a significant difference in terms of exceeding safe limits. Further, studies looking at health outcomes did not find any significant difference between consuming organic vs conventional produce. These studies are limited in number and duration, however. Further, there may be a bias in how these studies are performed. Organic farming does use pesticides, but only “natural” pesticides are allowed. There is little to no evidence that these organic pesticides are less harmful for consumers or the environment. It is just assumed that they are based upon the naturalistic fallacy.
Even if we take the most pro-organic assumption – that there are more pesticides on conventional produce and that those pesticides have greater negative health effects than organic pesticides, it must still be recognized that simply washing fruits and vegetables effectively reduces pesticide residue. If minimized exposure to pesticide residue is your goal, thoroughly washing your produce is probably the easiest and cheapest way to achieve that end.
Differences in bacterial contamination were similar. There were no differences seen in E. coli contamination. There was a 33% greater chance of isolated a multi-antibiotic resistance bacteria on conventional produce, but no evidence this translates into a health risk. Again – even if we assume a difference in health risk (something not demonstrated by the data) this can be remedied by thorough washing.
The recent review of organic vs conventional produce agrees with previous systematic reviews that there is insufficient evidence to conclude that organic produce is healthier or more nutritious that conventional produce. Despite the scientific evidence, the alleged health benefits of organic produce is the number one reason given by consumers for buying organic. This likely represents the triumph of marketing over scientific reality.