The antioxidant-based O2 Diet is relatively simple. Instead of counting calories, dieters add up ORAC points, short for oxygen radical absorbance capacity.

The ORAC number reflects the potential antioxidant activity of a food, as defined by the U.S. Department of Agriculture. In general, berries, nuts and teas have high ORAC values.

But eating according to ORAC won't necessarily make you any healthier, experts warn. ORAC testing is not standardized across the industry, and it was never designed to compare two foods, such as cranberries versus blueberries. Everything from the variety and age of a fruit or vegetable to how it is stored can affect the score.

Most importantly, however, a higher ORAC value has little relevance to health because the score "compares antioxidant capacity in a test tube, which may or may not work in the body," said biochemist Barry Halliwell.

So while exotic and pricier "superfruits" such as acai, baobab and mangosteen may have a high antioxidant value, they don't necessarily confer more health benefits than an apple grown in your backyard.

"How an antioxidant works (in the body) is probably more important than the quantity," said Toren Finkel, of the National Heart, Lung, and Blood Institute.

Still, consumers will likely see more ORAC numbers in advertising and on labels. According to a presentation by the market research firm Euromonitor International, "antioxidant measure clearly printed on product packaging is the way forward!"