Bill Lands, a retired biochemist living in Maryland, knows how to tell the difference. He created a free, albeit clunky, computer program called Keep It Managed that details omega fat levels in various foods. Kidney and pinto beans trump chickpeas, for example, and winter squash, spinach, broccoli, and cauliflower beat corn. Alaskan king crab and shrimp? More omega-3 than -6. So Lands, 78, eats seafood nearly every night.