You'll find antioxidant claims made not just for dietary supplements, but also for everything from juice, cereal, and power bars to tea, chocolate, and even bottled water. "Antioxidant"—a substance that helps mop up cell-damaging free radicals—has become synonymous with overall good health and disease prevention.

A more recent trend is for companies to advertise specific antioxidant levels or "scores," or to compare their products to others in antioxidant power. For instance, new cereals from Silver Palate boast 7,300 ORAC units per 100 grams, while Mystic Harvest Purple Corn Tortilla Chips list 6,000 ORAC units (ORAC, which stands for oxygen radical absorbance capacity, is one of several measures of antioxidant status developed by scientists). A baobab fruit powder that you add to oatmeal, yogurt, or other foods lists an ORAC value of 1,400 per gram. And tea extracts from Green Cell Technologies claim to have ORAC scores of up to 1.7 million per 100 grams.

It's hard to say what all those numbers mean. But they probably don't mean a whole lot in terms of health. The science and significance of antioxidants is much more complicated than a single number on a package can convey. The FDA has issued warnings against Lipton and other companies for making misleading and illegal claims about antioxidants—but many other iffy ones slip through the cracks.

Alphabet soup

Despite all the label claims, there's no standardized method for measuring antioxidant status and no official definitions for antioxidant capacity, ability, activity, power, efficiency, or other words you might see on packages or websites. Rather, scientists have developed a variety of tests, all with four-letter acronyms—besides ORAC, there are TEAC, TOSC, FRAP, TRAP, and others. These don't necessarily measure the same things or provide consistent results. For instance, a 2009 study in Food Chemistry noted that TEAC, which is simpler and cheaper, underestimates the antioxidant capacity of some foods, compared to ORAC.