By Roff Smith, National Geographic

LONDON—Everyone’s done it: You reach into your fridge and pluck out something tasty that you’ve meaning to eat but had half-forgotten about, only to discover that its “best before” date passed a few days earlier.

What to do? If you’re like many people, you let out a resentful sigh and toss it — better safe than sorry —  and resolve to be more watchful, less wasteful, in the future.

But did you really need to throw away that perfectly good-looking (and good-smelling) wedge of manchego or container of ice cream?

Depending on what it was, and how well it was kept, probably not, says Emma Marsh, who leads Love Food Hate Waste, a U.K.-based group that’s dedicated to tackling food waste. “More than half of the food we throw out is food we could have eaten,” she says, referring to British consumers.

Food waste is a growing global concern, with 1.3 billion tons of food — as much as a third of the food that is produced on the globe each year, worth over $750 billion — going to waste each year, according to the United Nations’ Food and Agriculture Organization. Aside from the morality of such loss in a world where an estimated 800 million people go to bed hungry each night, the economic and environmental implications are staggering. More than a quarter of the world’s agricultural land is being worked to grow food that nobody eats.