Americans throw away about 40 percent of the food they buy every year, at a cost of about $165 billion. And it's not in the form of uneaten table scraps. All of that food is wasted, according to researchers at Harvard University and the Natural Resources Defense Council, because of misleading, inconsistent labeling that is misconstrued by consumers.

Nutrition and content labeling is standardized at the federal level. But freshness labeling is done under 41 different state laws, while nine states do not require such labels.

In their study, the researchers said 90 percent of Americans regularly discard perfectly good food because they believe the "sell-by" dates on containers are safety warnings. Sell-by dates, the researchers said, actually are used by retailers for inventory control. Other date labels, such as "use by" or "best before" reflect manufacturers' estimates of peak quality.

Wasted food not only wastes potential nutrition, it wastes billions of gallons of water, petroleum, fertilizer and packaging. And since most of it ends up in landfills where it decomposes, it generates substantial amounts of methane and related greenhouse gases.

The researchers noted that the U.S. Food and Drug Administration and the Department of Agriculture have regulatory authority to standardize date labels. They should do so to clarify the meaning of the labels for consumers and to help reduce food waste. And, as recommended by the study, the labels should include a "freeze by" date to encourage preservation, rather than disposal, of perfectly sound food.