A few decades ago, corn oil was king of the cooking oils, promoted by doctors as being the most heart-healthy of all. Saturated fats were bad and should be avoided at all costs. Kind of simple.

Now, we're are overwhelmed with choices in cooking oil, from extra-virgin olive oil to coconut, and are bombarded by advice from nutritionists and doctors about which one to choose. Is coconut oil good, or a villain? Olive oil? flaxseed?

To provide some clarity, Fox News asked Keri Gans, R.D. and author of The Small Change Diet to provide some facts on how to choose a cooking oil.

First, all oils are high in calories, regardless of which one you choose. All oils contain about 120 calories and 13 grams of fat in every tablespoon. The difference is the ratio of saturated fats, to monounsaturated fat (MUFA), to polyunsaturated fat (PUFA). The ratio determines the oils' basic characteristics: whether it's solid or liquid, how it reacts to high temperatures, such as frying, and what effects it has on the body, says Fox.

Fox suggests choosing "cold-pressed" or "expeller-pressed" oils because they retain flavors and nutrients that are destroyed by heat. If you're frying, choose an oil with a high smoke point, so the oil won't break down during cooking. Cook with MUFAs because they won't break down into body-damaging compounds as quickly as PUFAs.

For most cooking, Gans advises choosing oils that are mostly MUFA, including olive, canola, sunflower, sesame, and soybean.

You should also try to maintain a balance of omega-3 and omega-6 fatty acids, which are types of PUFAs. Researchers have found that our diets contain too many omega-6 oils, which are found in plant oils, and too few omega-3 oils, which are found in fish oils.

Some cooking oils contain omega-3s. "Ideally, it's best to seek out oils with a more favorable ratio of omega-3 to omega-6, like walnut, canola, and flaxseed," Gans told Fox.
Below is Fox's choice in oils:

Olive: 77 percent MUFA, 9 percent PUFA, and 14 percent saturated. Olive oils are high in polyphenols, which are antioxidant compounds that have anti-inflammatory properties and may fight heart disease and cancer, and give the brain a boost.

Flaxseed: 18 percent MUFA, 73 percent PUFA, and 9 percent saturated. High amounts of omega-3s, which are heart-healthy.

Canola: 61 percent MUFA, 32 percent PUFA, and 7 percent saturated. Great for all-around cooking since it has a high smoke point, and has more omega-3s than most plant oils.

Avocado: 71 percent MUFA, 13 percent PUFA, and 12 percent saturated. High in vitamin E, avocado has a high smoke point.

Walnut: 23 percent MUFA, 63 percent PUFA, and 9 percent saturated. Walnut oil has a good omega-6 to omega-3 ratio.

Fox puts sesame, peanut, sunflower, and palm fruit oil in their "second choice" category. Grapeseed, coconut, soybean, and corn oil fall into the "think twice" category.