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The question

What's the healthiest oil to cook with?

The answer

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All cooking oils are healthy since they're made from plant sources.

Cooking oils are unsaturated and contain mainly monounsaturated or polyunsaturated fats. (Butter is predominantly saturated fat, the type that raises LDL blood cholesterol.)

Olive oil is the richest source of monounsaturated fat and has been shown to help lower blood pressure and LDL (bad) cholesterol and raise HDL (good) cholesterol. Olive oil also contains phytochemicals thought to help dilate blood vessels, prevent blood clots and decrease inflammation in the body.

Extra virgin and virgin olive oils are "cold pressed" from olives and, as a result, retain the more phytochemicals and nutrients compared to "pure olive oil", "olive oil" or "light olive oil", which have been refined.

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

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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.

Which oil you choose will depend on how you intend to use it. Heating oil can change its nutritional properties. Safflower, sunflower, canola, corn, grapeseed, peanut, almond, avocado, and refined olive oils have a higher smoke point and are well suited for high heat cooking. (The "smoke point" refers to the temperature at which a cooking oil starts to break down and burn.)

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; use them as a condiment or in salad dressings.

My advice is to keep a few small bottles of different healthy oils in your pantry.

Send dietitian Leslie Beck your questions at She will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail web site. Your name will not be published if your question is chosen.

Read more Q&As from Leslie Beck.

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The content provided in The Globe and Mail's Ask a Health Expert centre is for information purposes only and is neither intended to be relied upon nor to be a substitute for professional medical advice, diagnosis or treatment.

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