Who isn't guilty of leaving a head of lettuce in the fridge until it turns brown, allowing leftovers to mold or finding green slime in the bottom of the veggie compartment?

The United States has a terrible food waste problem. A family of four here throws out up to 25 percent of the food and beverages they buy, some of which ends up in landfills and contributes to greenhouse gases, according to a British scientific journal. The estimated cost: About $1,365 to $2,275 worth of food every year.

From farm to fork, in fact, up to 40 percent of the food in the United States goes uneaten, according to a study from the Johns Hopkins Bloomberg School of Public Health. Meanwhile, one in six Americans go to bed hungry, according to the hunger-relief organization Feeding America.

So what can you do to save money and help the planet? Plenty, according to chefs, food entrepreneurs and other experts.

Related: 10 Surprising Ways to Help the Planet

Rethink the way you shop and cook

Professional kitchens are doing their bit in the war against food waste. Across the country, professional chefs are touting “root to stalk” cuisine – using every part of the vegetable to minimize waste and maximize flavor. University dining halls are tracking food waste through digital platforms such as Lean Path so they can devise strategies to avoid the waste.

Here are some tips from conscientious chefs and other food-waste experts that you can use in your own kitchen.

Buy less. Try to get over the mindset of filling your fridge to the brim, advises Jonathan Broom, author of "American Wasteland: How America Throws Away Nearly Half of Its Food (and What We Can Do About It)." If you shop once a week, leave a night or two open for repurposing leftovers. Also, replenish perishables only after you’ve finished what’s in the fridge.

FIFO your fresh food. FIFO stands for “first in, first out.” Move older produce to the front of the fridge when unpacking new groceries so you’ll use it up before it goes bad.

Load up on "ugly" fruits and veggies. "Buy something imperfect today," advises celebrity chef Alex Guarnaschelli. A few blemishes never hurt anybody and you'll save produce that otherwise might go unsold. In the United States, the organization End Food Waste is petitioning grocery chains and others to sell less-than-perfect produce in its Ugly Fruit and Veg Campaign, supported by food movement heavyweights such as food writer Michael Pollan and star chefs Alice Waters and Jamie Oliver.

Keep an inventory of what you throw out for a couple of weeks. In her forthcoming book "Waste Free Kitchen Handbook," scientist Dana Gunders, MS, recommends using your phone to take pictures of what you're throwing out, then adjust your buying habits as needed.

Befriend the freezer. If you don't think you're going to use up that extra tomato sauce or loaf of French bread, freeze it for future use. Label and date containers of sauces, soups and stews — which all freeze well — to jog your memory in the future. Consider buying more frozen fruits and veggies, too.

Check out "root to stalk" recipes. Veggie trimmings are getting a star turn: Carrot-top pesto anyone? How about candied fennel stalks? Sprouting all over the place are use-it-all cookbooks, including New York chef April Bloomfield's "A Girl and Her Greens" and food writer Tara Duggan’s "Root to Stalk Cooking."

"Finely chopped carrot tops in a salsa verde add just the right hint of bitterness, celery leaves give extra crunch to a salad and asparagus stalks make a perfect stock for asparagus soup,” says Duggan. But check first: Not all stalks and seeds are safe for eating. Rhubarb leaves, for example, are toxic if ingested. When in doubt, check with the American Association of Poison Control Centers.

Get creative with leftovers. Sure, you can always reheat mashed potatoes, but you can also turn them into potato pancakes or potato croquettes. Stale bread can find a new home in Sicilian tomato soup (pappa al pomodoro) or bread and tomato salad (panzanella). Leftover rice is crucial to many Chinese and Thai dishes. And classic French sauces "depend on meat stocks made from bones and scraps," notes Tamar Adler in her recent ode to sustainable cooking in the New York Times and her book "An Everlasting Meal: Cooking with Economy and Grace."

Reduce portion size. Erring on the side of generosity results in what food experts call "plate waste" — uneaten food headed for the compost bin or (shudder) the garbage. Try giving everyone small servings the first time around or serving dishes family-style, in which people help themselves.

Related: Does Your Diet Pass the MyPlate Test?

Learn how to use expiration dates. "Use by" and "sell by" dates may tell you when the food quality is best, but that’s not necessarily the "toss by" date, says Bloom. Milk, yogurt and eggs can often be used after the expiration date if stored properly, for example — eggs should last three to five weeks in the refrigerator regardless of the expiration date, according to the U.S. Department of Agriculture. Let your eyes, sense of smell and taste be your guide.

Discounts on surplus food? There’s an app for that

App developers have created easy ways for consumers to connect with grocery stores to buy excess edibles at a discount before they’re thrown away. One example: Pare Up of New York City, which promises to help eaters save money while "helping retailers keep good food from the trash."

Other apps come at the food waste challenge by matching restaurants that have extra food with hungry customers looking for deals. Leloca is one example. Potential diners get a hefty discount — typically 30 to 50 percent off — when there’s an open table, since uneaten prepped food in the restaurant could end up trashed. (With the exception of items like fish, fresh pasta and meats like lamb that are served medium or rare, almost all restaurant food is prepared in advance.) The only catch: You have to redeem the deal within 45 minutes.

Some apps match food donors with people who need food. Waste No Food, a nonprofit founded by a 12th grader in the San Francisco Bay Area, is an online marketplace to reduce food that’s wasted daily by farms, restaurants and grocery stores. The app allows nearby food pantries, homeless shelters, and other charities to claim the surplus edibles.

A similar app from Feeding Forward, a San Francisco Bay Area non-profit devoted to what the organization calls "solving the world's dumbest problem," helps volunteers deliver food from donors to recipients. Komal Ahmad, 24, the founder of Feeding Forward, remembers being shocked by the hunger she encountered among the homeless in her neighborhood — many of them military veterans — when she attended the University of California at Berkeley. "By reducing food waste we save resources and money,” she says. “And most importantly, we move toward a world where everyone has enough to eat."

Related: Don’t Bug Out Over Indoor Composting

Sarah Henry is a food writer who has contributed to Grist, Afar, Civil Eats, KQED, the Washington Post, the San Francisco Chronicle, the Atlantic and other outlets. She is a contributing editor at Edible East Bay and a regular writer for Edible San Francisco. She has also worked at Time Inc. and has a food blog called "Lettuce Eat Kale."