Stress makes plants nutritious.

Antioxidant vitamins, flavonoids and many other beneficial trace nutrients in fruits and veggies help defend plants from pests--and sometimes even the botanical equivalent of sunburn.

Food chemist Alyson Mitchell of the University of California, Davis and her colleagues reported February 13 that plants' varying capacity to generate these compounds may explain why certain varieties of nectarines, tomatoes and spinach offer diners a richer source of micronutrients.

The team's data also suggest an explanation for why organically farmed produce tends to make substantially more of these nutritious compounds than conventionally farmed produce. Relying on potent fertilizers and pest-control measures provides conventionally grown produce a relatively cushy life, diminishing the need to waste energy on defenses.

Selecting produce that is especially rich in stress-triggered micronutrients, including organics in some cases, might improve the nutrition of people who don't get the recommended servings of fruits and vegetables each day--which is most people, Mitchell concluded.