Christina Rivera hates to see food go to waste, so she is cracking down at her Silver Lake restaurant.

Rivera began weighing the trash generated by Gobi Mongolian BBQ House with an eye toward shrinking the pile of scraps, peels and other organic material. She put up signs noting that some 40% of the nation's food supply is thrown out each year.

Then she did something that put some patrons into a rage: On busy all-you-can-eat nights, the restaurant now charges an extra fee for any plate with leftover food.

One Yelp review calls the policy "cynical" and "insulting," referring to it as "transparent spin, which is obviously about their profit margin."

"It's had a mixed reception," Rivera, who co-owns the eatery, acknowledged. "Some people are really receptive to it; other people say we're doing it because we don't want to spend money buying more food."

Like Rivera, much of the U.S. food industry is starting to talk trash.

They're responding to studies showing that annual U.S. food waste has risen 30% in the last three decades. It gets worse during the holiday season, when Americans chuck three times more food.

Waste reduction used to happen mostly by accident. Some restaurants trimmed portion sizes to appeal to health-conscious consumers. Food drives and donations to soup kitchens helped prevent products from spoiling in pantries.

But sustainability rhetoric is at a fever pitch these days, fueling trends such as whole-animal dining, with restaurants offering offal and other exotic cuts shunned in the past. At Animal Restaurant in Los Angeles, pig heads are picked clean for the popular pig's ear plate and other dishes. The collar of the fish — a part often thrown out — used for the popular kampachi tostada dish is set aside and served as a special.

Experimenting chefs at establishments such as Thank You for Coming in Atwater Village change their menu daily to reflect whatever ingredients happen to be in the refrigerator and pantry instead of buying surplus. Chefs try to reduce food waste by pickling and dehydrating food while composting as much as possible.

Rivera's husband, Mike, runs the local Pazzo Gelato chain, where he tries to grate, garnish or boil fruit peels instead of tossing them.

In April, more than 100 restaurants — including Chipotle and Momofuku — signed on for New York's first Food Waste Challenge, promising to divert half their food waste from landfills. Advocacy group Feeding the 5000 saved about 1 ton of food from waste bins in September, inviting hundreds of New Yorkers to prepare surplus or blemished produce for a mass meal.

For many restaurant operators, reasons for joining the fight against food waste may be as much financial as philosophical.

Industry growth has been stagnant this year. Restaurateurs are worried about the effect of minimum wage hikes and healthcare reform on their balance sheets.

Ingredient prices are near record highs, pushed by volatile weather, inflation and limited agricultural resources. Many owners are hoping to scale back food costs, which typically use up a third of the average restaurant's revenue.

Losses from food waste don't help. The cost of wasted food around the world, excluding seafood, is about $750 billion a year — an amount equal to Switzerland's economy, the U.N. said. For commercial food operators, that amounts to $40 billion a year, according to the U.S. government.

"Restaurants are a tight-margin industry where any penny saved is good," said Scott DeFife, an executive vice president with the National Restaurant Assn.

Some have turned to Portland, Ore., company LeanPath, whose ValuWaste automated tracking system monitors trash in commercial kitchens. Its revenue surged after the recession, booming 54% two years ago, doubling last year and potentially heading for a repeat this year, founder Andrew Shakman said.

The system uses scales, cameras and touch screens to record items — trimmed meat, burned bread, dropped ingredients — as they're being discarded. Users spend a few seconds writing notes, which are sent wirelessly to a data center to be analyzed.

Some restaurants have invested in smart refrigerators that can predict — via mold sensors and scanned expiration dates — when food will go bad.