For years, studies showed no nutritional difference between organic and conventionally grown food. That’s because scientists were looking at macronutrients — vitamins A, B, C, and so on.

But they’ve since learned that macronutrients are only part of the nutrition story. It turns out that there are all sorts of compounds like antioxidants and phytonutrients — known collectively as micronutrients — that fight cancer, impede aging, and maintain heart health.

And if organic and conventional food are roughly identical in macronutrient content, organic appears to be far superior in terms of micronutrients.

The latest evidence comes from a four-year study from Newcastle University in the U.K. The results are preliminary; they haven’t been published in a peer-reviewed journal yet. Here is The Independent:

An EU-funded investigation into the difference between organic and ordinary farming has shown that organic foods have far more nutritional value. Up to 40 per cent more antioxidants, which scientists believe can cut the risk of heart disease and cancer, could be found in organic fruit and vegetables than in those conventionally farmed.

Evidently, it’s the most extensive study of its kind yet completed. But other studies have shown similar results. In his New York Times column earlier this month, the distinguished food-science writer Harold McGee reported on a study showing that rats — unbiased by either food-industry marketing or by wild hippie health claims — prefer organic to conventional food:

A team of Swiss and Austrian scientists recently concluded a 21-year study of organic wheat production. As an ;integrative method” for assessing quality, they gave lab animals a choice of biscuits made from organic or conventional wheat. The rats ate significantly more of the former. The authors call this result remarkable, because they found the two wheats to be very similar in chemical composition and baking performance.

What can this mean? McGee posits that it’s all about the phytochemicals — chemicals that plants evidently produce to repel insects and other threats. Organically cultivated plants evidently produce more phytochemicals to survive without pesticides. Phytochemicals, McGee says, carry both flavor and health benefits.

What do phytochemicals have to do with flavor? Phytochemicals are chemicals created by plants, and especially those that have effects on other creatures. Plants make many of them to defend themselves against microbes and insects: to make themselves unpalatable, counterattack the invaders and limit the damage they cause. Most of the aromas of vegetables, herbs and spices come from defensive chemicals. They may smell pleasant to us, but the plants make them to repel their mortal enemies.

For evidence that organically grown plants contain more micronutrients, McGee points to a peer-reviewed study out of the University of California. The study showed significantly higher levels of antioxidants in organic tomatoes than in conventional.