Americans toss out a lot of perfectly good food. In fact, it is estimated that 30 to 40 percent of the U.S. food supply is wasted. Those expiration dates printed on food packages are partly to blame, a new study suggests, especially when it comes to food that is stored in the refrigerator.

In the first study to use actual data from refrigerators in the homes of Americans, researchers at The Ohio State University examined why people discard food and hoped to identify opportunities to help reduce food waste. The State of the American Refrigerator web-based survey used information gathered from 307 initial survey participants and 169 people who participated in follow-up surveys.

Most people don't understand what the “Use by,” “Sell by,” and “Best by” dates on food packages mean. It is not necessarily unsafe to eat food after that date.

People who took part in the study were asked what fruits, vegetables, meats and dairy were in their refrigerator and how much of it they expected to eat. A week later, researchers followed up to find out what actually happened to the food. They questioned the participants about a variety of factors that could have led them to throw out food, such as the date on packages, odor, appearance and cost.

The participants usually thought they'd eat twice what they ended up eating. They expected they would eat about 97 percent of the meat in their refrigerators, but actually ate only about half. They anticipated eating 94 percent of the vegetables, but only ate 44 percent — less than half. They thought they would eat 71 percent of fruit, finishing only 40 percent, and predicted they would finish 84 percent of dairy, but only consumed 42 percent.

People who cleaned out their refrigerators the most wasted more food, and people who checked nutrition labels more often wasted less food. Younger people were less likely to use all of the items in their refrigerators, while those 65 and older were less likely to be wasteful.

Worries about the odor or appearance of food or the dates printed on food packaging were among the top factors that caused people to be concerned about the safety of food and contributed to their decision to toss it out.

According to Brian Roe, senior author of the study, approximately 43 percent of food waste happens in the home, not in restaurants, supermarkets or on farms. This makes consumers the biggest contributors to the problem of food waste, as well as the most difficult group to reach regarding changing their food practices.

“Our results suggest that strategies to reduce food waste in the U.S. should include limiting and standardizing the number of phrases used on date labels, and education campaigns to help consumers better understand the physical signs of food safety and quality,” said Megan Davenport, a graduate student who led the study.

Most people don't understand what the “Use by”, “Sell by,” and “Best by” dates on food packages mean. They are not an indicator of a food’s safety, but a general guide as to how long a food product will be at its best quality. It is not necessarily unsafe to eat food after that date.

Here's a guide to commonly used phrases and what they mean:

  • Best if Used By/Before — This date signifies when a product will be at its best quality or flavor.
  • Sell-By — This simply tells the store how long to keep the product on the shelf for inventory management.
  • Use-By — This is the last date recommended for using a product at its best quality. Exception: On infant formulas, it IS a safety date.
  • There is currently a proposal before Congress that would clarify date labeling rules and hopefully help to reduce food waste.

    The study is published in Resources, Conservation & Recycling.