Countless kitchen squabbles go something like this: Someone looks at the date on the lettuce and thinks it has gone bad. The other person says it is perfectly fine. So who is right?

In the U.S., about 30% to 40% of all food is wasted, or about $161 billion worth of food, according to Agriculture Department estimates. While it is unclear how much of that is due to consumers misreading date labels, a recent survey of over 1,000 grocery shoppers by the Food Marketing Institute, a trade association for grocery stores, showed that...