The ongoing debate over the health benefits of organic food

Recently I wrote a post about a video by Dr. Aaron Carroll in which he described the results from a meta-analysis on the health benefits of organic food. He concluded that basically there were none (with a few minor caveats):

"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."

Imagine my surprise last week when I opened my Google News Health webpage and saw the headline "Large Study Shows Organic Foods Are Safer, Healthier than Nonorganic", and beneath that article was another with the subtitle "A new study claims organic fruit and vegetables can lead to better health". And so the debate continues.

First some background from my previous post: "Organic food is grown without the use of synthetic pesticides or fertilizers, antibiotics, or hormones. Organic food represents 4% of the food budget in the U.S. totaling $31 billion in total annual sales. It has become big business."

The new study analyzed 343 peer-reviewed articles and found the following (Telegraph):

"In one of the most comprehensive analysis to date researchers found that organically grown fruit and vegetables contain more of the antioxidant compounds linked to better health, along with lower levels of toxic metals and pesticides."

Vox.com examines these conclusions in greater depth and highlights some of the complicated and contradictory results in the literature. In this post I will focus on the statement about antioxidants.

The antioxidants in question are a class of chemicals called flavonoids. Flavonoids are polyphenolic compounds (e.g. phenolic acids, anthocyanins, and carotenoids) composed of two benzene rings joined together by a third ring. They are plant pigments and their primary function is to provide coloration for flowers and fruits. However they fulfill a variety of other roles including helping plants fight off pests that cause plant disease.

Indeed, one hypothesis is that "organic crops create more [flavonoids] since they're not protected by chemical pesticides and have to deal with more pests." The study mentioned above showed a 20-40% increase of certain flavonoids in organically-grown produce.

However the more important question is what is the evidence that flavonoids provide health benefits? The data are mixed. The two diseases which have captured the most attention are cardiovascular disease (CVD) and cancer. For CVD, some studies show a small modest reduction in relative risk caused by consuming flavonoids (link1) whereas others show no effect (link2). Likewise for cancer, the studies show either no benefit (link3) or only a small benefit (link4). The majority of articles conclude that the jury is still out and that more studies are needed. There are significant challenges interpreting the data because the studies are not randomly controlled trials (RCTs), the variety of flavonoids, the heterogeneity of people's diets, and confounding factors such as the fact that foods rich in flavonoids, i.e. fruits and vegetables, are generally healthful.

There are other reasons why scientists are skeptical. For example, it is not known whether flavonoids are absorbed by the body in physiologically relevant quantities, and by what mechanism they act to confer their healthful benefits. Indeed, more generally there has been controversy over the benefits of antioxidants as a class, not just flavonoids. A recent study in the New England Journal of Medicine (described in the Huffington Post) argued that antioxidant supplements do not reduce cancer risk.

Taken together, connecting the line from organic produce to flavonoids to health benefits is quite tenuous. More importantly, as Brad Plummer points out in the Vox piece, the bigger issue is getting people to eat enough fruits and vegetables which countless studies have shown to be healthful:

"By contrast, about 73 percent of the US population doesn't eat the recommended five or more servings of fruits and vegetables each day. For many nutritionists, that's a much more pressing concern — fixing that would swamp any of the health benefits organic food might have."

In other words, it is counterproductive to worry about whether an orange is organic or not if it prevents you from eating the orange:

"What's missing in this debate is the important fact that the best thing consumers can do is to eat lots of fruits and vegetables, period, regardless of whether they are produced organically or conventionally," says Carl Winter of the University of California, Davis. (He's also skeptical, by the way, that organic food is any healthier for you.)

One big reason why fruits and vegetables are healthy is because you can obtain a number of important nutrients including potassium, dietary fiber, folate (folic acid), vitamin A, and vitamin C without the fat and calories associated with meat or junk food. Indeed numerous studies have shown that a diet rich and fruits and veggies lowers your risk for cardiovascular disease, high blood pressure, and cancer [link].

Are you eating the recommended five servings of fruits and vegetables every day?

Figure 1. Organic or not, these fruits and vegetables look delicious and are quite healthy for you!