“I’ve become very sensitized to this because my wife is a relatively small person and I’m a relatively big guy,” Mr. Vilsack said. “She gets the same portion size as I do when we go to a restaurant, and sometimes we take it home but often we don’t because it’s really not the kind of food you can take home.”

Image Public and private programs are working to put excess food to good use, often returning it to the earth as compost. Credit... Kalim Bhatti for The New York Times

Bon Appétit started working to reduce food waste in 2005 and within four years had cut enough to equal a reduction of ton in greenhouse gases.

The reduction came through changes in portion size and preparation. Instead of discarding carrot peels, for example, the company’s chefs might use them to make stock. Or they might be challenged to come up with ideas for using all of a pig instead of just its choicest cuts.

The company also started daily waste monitoring at its restaurants and a program that allowed diners to weigh the amount of food left on their plates at the dish return station.

It has also worked with its food service accounts and local governments to create programs to reduce food waste. At the Seattle Art Museum, for instance, grab-and-go sandwiches are labeled to tell diners which leftovers can go in the compost bin. A spiced, stewed tomato and chickpea salad that was unused during a recent museum open house was donated to Food Lifeline, a nonprofit working to feed the hungry.

Since November, Taste, the museum’s restaurant and catering service, has donated roughly 600 pounds of food that otherwise would have gone to waste. “Often when we have events, we have a lot of food that never even goes out to the buffet that is perfectly good,” said Kristin White, the general manager.

The Food Recovery Network, with chapters at almost 50 colleges, picks up leftovers from university dining halls to distribute to food banks and soup kitchens. “The biggest challenge is this perception that it’s either unsafe to donate surplus food or that they might be held liable for someone getting sick or that it would just be this extra cost,” said Ben Simon, the organization’s founder and executive director.