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Olive oil regarded for heart-healthy properties, but it may not be the best choice

As a dietitian in private practice, it's a question I am often asked: What's the best cooking oil to use? With so many varieties and brands crowding grocery store shelves, choosing the right oil can be a challenging – and daunting – task.

And just because olive oil is highly regarded for its heart-healthy properties, it's not always your best choice. Knowing which oil to buy and how to use it isn't so black and white.

Ultimately, the cooking oil you pick should be based on how you intend to use it and your personal health concerns.

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Not long ago, cooking oils were something we strived to use less of. We were told to eat less total fat in an effort to lose weight, lower cholesterol and ward off certain cancers. But over the past decade studies have determined that certain fats can help lower blood pressure, guard against Type 2 diabetes, and ward off heart attack – and the message has changed.

Today, a healthy diet can contain as much as 35 per cent of its calories from fat – provided, of course, you choose the right type. In fact, Health Canada advises we consume two to three tablespoons (25 to 40 millimetres) of unsaturated fats each day to reap their health benefits.

Fats are classified as saturated or unsaturated (monounsaturated or polyunsaturated).

Saturated fat is found mainly in animal foods such as meat, poultry, eggs and dairy products. A high intake of saturated fat can boost LDL (bad) cholesterol and may increase the risk of prostate cancer.

Tropical oils – palm, palm kernel, coconut – are also highly saturated. Although coconut and palm oil raise total blood cholesterol, this effect is mostly due to their ability to increase HDL (good), not LDL cholesterol.

The bottle of cooking oil in your pantry contains predominantly polyunsaturated or monounsaturated fat. Both types can help lower blood cholesterol when they're substituted for saturated fat.

Excellent sources of monounsaturated fat include olive, canola, peanut, avocado and almond oils. Olive oil is the richest source of monounsaturated fat – 77 per cent of its total fat is derived from this type of fat.

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Studies have shown that 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.

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

Polyunsaturated oils provide essential fatty acids called linoleic acid and alpha linolenic acid (ALA). They're essential because your body can't make them on its own; they must be supplied by your diet.

Most of us already get plenty of linoleic acid, an omega-6 fatty acid that's widespread in processed foods made with soybean and corn oils. We don't, however, consume enough ALA, an omega-3 fatty acid found in flax, walnut, canola and hemp oils. (Although canola oil contains mainly monounsaturated fat, one-third of its fat is polyunsaturated.) Our excessive intake of omega-6 fats and our low intake of omega-3's is thought to play a role in the development of heart disease, cancer and autoimmune disease by promoting inflammation in the body.

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Studies suggest that higher intakes of ALA are protective from heart disease, especially if your diet lacks omega-3 fats from fish.

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.

Some cooking oils are also a good source of vitamin E, an antioxidant that protects cells from the harmful effects of unstable oxygen molecules (free radicals). The richest sources of vitamin E include grape-seed oil, almond oil and avocado oil.

When it comes to nutrition, the healthiest oils are those rich in monounsaturated fat, phytochemicals, and alpha linolenic acid. Extra virgin olive, canola, peanut, flaxseed, walnut, hemp, avocado and almond oils top the list.

But which oil you choose depends on how you intend to use it. Heating oil can change its nutritional properties. 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, grape seed, 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.

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.

Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.

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