• Question: With so many oils to choose from, which ones are the healthiest?

There are two main types of cooking oils - those mainly comprised of monounsaturated fat and those made up mostly of polyunsaturated fat. When to comes to good health, they both have advantages. Both can help lower blood cholesterol when they're substituted for saturated fat. But some cooking oils can do more.

Cooking oils high in polyunsaturated fat include sunflower, safflower, soybean, corn, grapeseed, hemp, flaxseed, and walnut.

Cooking oils made from monounsaturated fat include olive, canola, peanut, avocado and almond oils. Olive oil is the richest source of monounsaturated fat - 77% of its total fat is derived from this type of fat.

Adding monounsaturated fat to your diet can help raise HDL (good) cholesterol. Monounsaturated fat is also thought to improve how the body uses glucose among people with diabetes. Olive oil has received the most attention by scientists. Its monounsaturated fat helps lower blood pressure and LDL cholesterol and raise HDL cholesterol. Olive oil also contains phytochemicals that are thought to help dilate blood vessels, prevent blood clots, and decrease inflammation in the body.

But not all olive oils are created equal. Extra virgin and virgin olive oils are "cold pressed" from olives using minimal heat and no chemicals. As a result they retain the highest amount of phytochemicals and nutrients compared to "pure olive oil", "olive oil" or "light olive oil", which have been refined. Cold pressed oils retain their nutritional value as well as their natural flavour and colour. So there is no doubt that extra virgin olive oil is one of the healthiest.

• Question: Which other cooking oils top your list?

Polyunsaturated cooking oils high in an omega-3 fatty acid called alpha linolenic acid or ALA are good. ALA is an essential fatty acid that your body can't make on its own - you must get it from your diet. Studies suggest that higher intakes of ALA can protect you from heart disease, especially if your diet lacks omega-3 fats from fish.

The best sources of ALA are flaxseed oil, walnut oil, hemp oil and canola oil.

Women require 1,100 milligrams of ALA per day and men need 1,600 milligrams. One teaspoon (5 ml) of flax oil delivers 2,400 milligrams of ALA, a teaspoon of walnut oil has 470 milligrams and a teaspoon of canola oil has 419.

• Question: Can heating cooking oil change its nutritional properties?

Yes! So the oil you decide to buy also needs to be based on how you intend to use it. Some of the healthiest oils become unhealthy when heated above certain temperatures. The "smoke point" refers to the temperature at which a cooking oil starts to break down and burn. In general, lighter coloured more refined oils have a higher smoke point and are best suited for deep-frying, stir-frying and sautéing.

Safflower, sunflower, soybean, sesame, canola, corn, grapeseed, peanut, almond, avocado, and refined olive oils have a higher smoke point.

Unrefined oils such as extra virgin and virgin olive oil have a lower smoke point and are best used for salad dressings and marinades.

Flaxseed, walnut and hemp oils should not be used for cooking since heat destroys their essential fatty acids. These oils should be used as a condiment or in salad dressings and stored in the refrigerator.

Nut oils such as walnut, almond, hazelnut, macadamia, and pumpkin seed have a distinctive rich taste. Use them in dressings or to flavour light dishes at the end of cooking.

• Question: How long can you keep cooking oil? And how should it be stored?

Regardless of the oils you choose, buy only what you'll use within one year. Most cooking oils have a limited shelf life and turn rancid quickly if exposed to light, heat and air. If they smell rancid, throw them out. Rancid oils have an unpleasant taste and have diminished nutritional value. Store cooking oils in a cool, dark cupboard or the refrigerator.