Dec 06 2011

Organic Food, Pesticides, and Cancer

I recently received the following question:

My wife is worried about eating vegetables that have been treated with pesticides for fear that it increases risk of cancer. I have looked at some of the books she has read that pushes organic eating and I was not impressed with the authors credentials or citations. Is there any scientific evidence that supports the assertion that eating organic vegetables will reduce the risk of cancer?

Organic farming is a complex issue, and one of those issues shrouded with ideological belief to the point that it is often difficult to find objective evidence and opinion. There are also many issues within the organic farming framework. Is organic farming cost effective, more sustainable, capable of feeding the world, better for the environment, and better for human health? There is also the more fundamental question – what, exactly, constitutes organic farming? I find that often it is a catch-all phrase for any farming practice deemed to be more sustainable or environmentally friendly, or any practice considered “natural”. Unfortunately “natural” is a vague term.

Here is part of the USDA definition for organic:

“Organic agriculture is an ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. It is based on minimal use of off-farm inputs and on management practices that restore, maintain and enhance ecological harmony.

The devil, as always, is in the details – what, operationally, does this mean? Here there is agreement on some details but not on others. You can search the USDA site linked to above for more details.

My opinion is that farming practices should each be judged on their own merits, utilizing the best evidence available. I find this situation similar to the “alternative medicine” category, which is sweeping in its philosophy but with no clear operational definition, and eager to claim for itself practices which are solidly science-based (like legitimate uses of nutrition, physical therapy, or even exercise). Organic farming seems better than CAM as a category, but still represents a false dichotomy, in my opinion. Is any sustainable practice organic? What difference does it make what the source of a pesticide is?

I agree with many of the organic principles – like sustainability, low environmental impact, and food safety. Who would be against sustainability in agriculture? I would prefer, however, an evidence- based rather than philosophy-based (which, for organic farming, is essentially the naturalistic fallacy) approach to what works.

My big problem with the “organic” label is when it is applied to produce rather than farming practice. It is used as a marketing device, implying greater nutrition and safety. However, the evidence is simply not there to back up such claims.

A recent review of the published research from 1958-2008 showed that the evidence does not support the conclusion that there is any nutrition-related health benefit to eating organic food. Fifty years is a long time for organic food advocates to have made this case, but they haven’t. It also seems, however, that there hasn’t been a great deal of high quality research in this area, so it seems that the confidence in this conclusion of a lack of benefit is still open to better research.

Other studies look simply at the nutritional content of organic vs traditionally farmed produce.  The same researchers did a systematic review of this question and found:

On the basis of a systematic review of studies of satisfactory quality, there is no evidence of a difference in nutrient quality between organically and conventionally produced foodstuffs. The small differences in nutrient content detected are biologically plausible and mostly relate to differences in production methods.

Some studies have found small increases in nutritional content in organic produce. However, it is possible that this is mostly or even entirely due to the fact that organic produce tends to be a little smaller with lower water content, and so higher concentrations of measured nutrients. It is still not clear, therefore, that eating organic produce will deliver more overall nutrients than eating traditional produce, and if there is a difference if it is clinically relevant to health.

This brings up yet another issue – organic produce is more expensive. The USDA lists comparisons of organic and conventional produce prices and finds that there is a premium for organic produce. Looking through some of the tables is seems that organic produce is more than twice as expensive as conventional produce. Another USDA site, however, finds that 40% of organic farmers at farmers markets did not charge a premium for their organic produce, although this varied by season and crop.

Regardless of the reasons for the price difference, there is still a premium for most organic crops. Given the small, if any, nutritional advantage, it’s possible that higher organic food prices might result in a net decrease in consumption of fruits and vegetables.  In any case, the evidence for nutritional health benefits does not support paying a higher premium for organic produce (although there are many other reasons why someone might prefer organic and be willing to pay a higher price, but they are separate issues outside the scope of this post).

What about the issue of pesticides? Here is where the “organic” concept is most guilty of committing the naturalistic fallacy. The organic label does not mean pesticide free. It just means that “naturally derived” pesticides are used instead of “artificial” pesticides. There is no a priori reason, however, to assume that naturally-derived pesticides are safer. It mostly means that they are less well-researched, because of the false assumption that they are safer.

Again – this is a very complex area in itself. To summarize what I have found: pesticides are poisons, there is no question, and all efforts should be made to limit human and environmental exposure. This does not mean they cannot be used safely, but precautions need to be taken. There is no reason to assume organic pesticides are safe or safer than conventional pesticides. There is evidence that organic pesticides are often less effective, requiring greater amounts to be used, which can have a net negative effect on the environment. When studied it turns out that organic pesticides can also have carcinogenic effects.

Here is a good summary of the evidence.

While organic produce has lower levels of pesticides than conventional produce, there is no evidence that these low levels of pesticides pose any health risk. For those who wish to minimize their pesticide exposure, just in case, buying organic may not even be the best option. Washing your fruits and vegetables works quite well in reducing pesticide residue. It’s also cheaper than buying organic.


While the overall issue of organic farming is complex with many sub-issues, the question of health benefits is perhaps the easiest to answer at this time. After decades of research there is no evidence for any health benefits to eating organic vs conventional food. Nutritional value is either slightly higher or not significantly different in organic produce, but even with a generous interpretation is not clinically significant.

The issue of pesticides has not been completely resolved, but at present the levels of pesticides in conventional produce is likely to be below safety limits, and there is no real reason to conclude that “organic” pesticides are any safer. Further, the most effective means of minimizing pesticide exposure is simply to thoroughly wash your fresh produce.

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