and blackberries grown in neighboring plots using different methods (including organically and conventionally) were compared for level of vitamins and polyphenols. Polyphenols are a group of secondary metabolites manufactured by plants that we’ve recently learned play an important role in human health and nutrition. Many are potent antioxidants, some play a role in preventing or fighting cancer; others exhibit anti- microbial properties. The Davis researchers found that organic and otherwise sustainably grown fruits and vegetables contained significantly higher levels of both ascorbic acid (vitamin C) and a wide range of polyphenols.

The recent discovery of these secondary metabolites in plants has brought our understanding of the biological and chemical complexity of foods to a deeper level of refinement; history suggests we haven’t gotten anywhere near the bottom of this question, either. The first level was reached early in the nineteenth century with the identification of the macronutri- ents - protein, carbohydrate, and fat. Having isolated these compounds, chemists thought they’d unlocked the key to human nutrition. Yet some people (such as sailors) living on diets rich in macronutrients nevertheless got sick. The mystery was solved when scientists discovered the major vitamins - a second key to human nutrition. Now it’s the polyphenols in plants that we’re learning play a critical role in keeping us healthy. (And which might explain why diets heavy in processed food fortified with vitamins still aren’t as nutritious as fresh foods.) You wonder what else is going on these plants, what other undiscovered qualities in them we’ve evolved to depend on.

Michael Pollan: The omnivore's dilemma, A natural history of four meals, Penguin Books, New York, 2006.