Butter melts in a skillet. (Sarah L. Voisin/THE WASHINGTON POST)

Are you prepared to temper your tallow consumption and swap shortening for safflower oil?

The federal government’s 2010 Dietary Guidelines for Americans urge us to reduce our intake of “solid fats” such as saturated and trans fats by replacing them with more healthful, unsaturated fats and oils. The former are believed to increase risk of certain chronic conditions and diseases, while the latter may help protect against them.

Robert Post, deputy director of the U.S. Department of Agriculture’s Center for Nutrition Policy and Promotion, says Americans are getting “far too many” of their calories from fat, especially solid fat.

“That leads to development of fatty tissue and weight gain,” Post explains, “which promotes hypertension, cardiovascular disease, coronary heart disease and chronic diseases related to the diet like diabetes.”

“Decrease the amount of certain fats in the diet,” Post adds, “and you potentially reduce the risk of those health outcomes and may even live longer.”

Setting aside the matter of disease risk, there’s compelling reason to keep an eye on the solid fats in your diet. Because solid fats are highly caloric, and because foods containing a lot of them also tend to have lots of sugar, reducing consumption is an excellent way to cut calories while leaving room for more nutritious foods on our plates. And that’s something most of us could use.

Kinds of fat

The fats we eat are made up of different combinations of three kinds of fatty acids: saturated, monounsaturated and polyunsaturated. Fats containing mostly saturated fatty acids or trans fatty acids (more about those in a moment) are solid at room temperature and are thus considered solid fats. Fats containing mostly unsaturated fats are liquid at room temperature and are called oils.

Saturated fats typically are found in animal-based foods, including meats and dairy products. Major sources of saturated fats in our diets, according to the guidelines, are cheese, pizza, grain-based desserts (think cookies, cakes and pies baked with saturated fats) and dairy desserts (such as ice cream). The dietary guidelines say we should limit saturated fats to 10 percent or less of our daily caloric intake.

Unsaturated fats include the essential (so-called because our bodies don’t produce them) fatty acids known as omega-3 and omega-6. Unsaturated fats usually come from plants (including avocados, seeds and nuts) but are also found in some fish and shellfish (such as salmon, mackerel and tuna). These fats are believed to promote cardiovascular and overall health and may even help ward off Alzheimer’s disease.

(Confusingly, a handful of plant oils — such as coconut, palm kernel and palm oils — are considered solid fats because they are semi-solid at room temperature and have similar effects on our bodies as saturated and trans fats.)

Trans fats are technically unsaturated fats. Although some trans fats occur naturally in the meat and milk of grazing animals such as cows, some of the trans fats in our diets are created through a process called hydrogenization. When trans fats are partially hydrogenated, most of their unsaturated fatty acids are converted to saturated fatty acids. The process is what makes them solid at room temperature — turning them into those unhealthful solid fats. In 2006 the federal government required food manufacturers to list the amount of trans fats on product packages; the use of trans fats has dropped dramatically since then.

Cholesterol is a fatty substance known as a lipid and is found only in animal-based foods. Our livers produce it, and it plays a key role in producing Vitamin D and hormones. Eating too many cholesterol-rich foods has long been blamed for raising blood cholesterol, which boosts cardiovascular disease risk. But some people seem to be able to enjoy foods with dietary cholesterol without affecting their blood cholesterol. The dietary guidelines suggest that saturated fat and trans fats may have a greater effect on blood cholesterol than dietary cholesterol does. Still, the guidelines call for most of us to limit cholesterol to 300 milligrams daily.

Calorie counts

“We do need some fat,” Post points out. Among other functions fats fulfill, our bodies need fat to benefit fully from the fat-soluble vitamins A, D, E and K. “If you eliminated it entirely, you’d have a deficiency issue.” But, Post adds, “our metabolic systems differ across our life span,” so we require different amounts of fat at different ages. Here’s a guide to the percentage of our daily calories that should come from fat:

—Ages 1-3: 30 percent to 40 percent.

—Ages 4-18: 25 percent to 35 percent.

—Ages 19 and up: 20 percent to 35 percent.

“If an adult on a 2,000-calorie diet devotes 400 to 500 calories to fat, that’s okay,” Post explains. Since a gram of fat has nine calories, that’s about 45 to 55 grams a day. Keep in mind that the total includes the healthful oils, too, which weigh in at 120 calories per tablespoon.

Tracking fat intake

When you’re keeping tabs on your fat intake, the Nutrition Facts panel is your best friend. That document, which appears on food packages, tells how many grams of total fat, saturated fat and trans fat and how many milligrams of cholesterol a serving contains, plus percentages of Daily Values (the amount of a nutrient recommended within a 2,000-calorie daily diet) for each kind of fat.

—Ingredient lists on food packages also provide useful information about the kinds of fats a food contains.

—Go easy on coconut oil, palm kernel oil, butter, beef fat (tallow), pork fat (lard), shortening and stick margarine.

—Embrace cottonseed oil, soft margarine, peanut oil, soybean oil, olive oil, corn oil, sunflower oil, canola oil and safflower oil.

Be fat savvy

There are obvious ways to literally trim “bad” fat from your diet: Remove visible fat from your steak before you grill it, for instance, and stick with skinless chicken breasts. Avoid stick margarines and shortenings containing partially hydrogenated oils. Choose low-fat salad dressings, or just drizzle your greens with vinegar and olive oil. Dip bread in a bit of olive oil rather than spreading it with butter. Saute or stir-fry in one of the healthful oils above. And switch to fat-free or low-fat milk.

Know the clues

Do restaurant menus have you baffled over fat content? You should know that there are some clues as to how fattening a dish may be.

More: For nutrition news, visit The Checkup blog, follow @jhuget on Twitter and subscribe to the Lean & Fit newsletter.