Nutrition columnist Carrie Dennett provides some tips on caring for your healthful oils.

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When it comes to what to eat, fat is a complicated topic. Any discussion of dietary fat and health should go beyond how much fat to eat and what types. It should also consider best practices for purchasing, storing and using fats and oils.

The most healthful high-fat foods include fish, nuts, seeds, olives and avocados and some of the healthiest oils come from these foods. I advocate buying the best quality you can afford of any food — from carrots to cookies — but this is especially important with fats and foods that contain them.

Choose organic, unrefined, cold-pressed oils whenever you can. Many pesticides are fat-soluble, which means they accumulate in fat. In addition, many mass-produced vegetable oils are subjected to chemicals and high heat during processing.

High-quality oils are more than just fat — they contain many of the healthful compounds that were found in the fruit, nut or seed they came from. How you store and use these oils is important, because light, air, heat and time can degrade them, destroying their nutrients and turning them rancid.

When oil goes rancid, because of overheating or poor storage conditions, healthful antioxidants in the oil also degrade. This can turn them into unhealthful — even dangerous — free radicals. (It’s even worse if you reheat and reuse vegetable oils.)

Store oils in a cool, dry place away from direct light, and sniff before using to check for unpleasant or “off” odors. If the oil is rancid, throw it away.

Oils and fats don’t respond the same way to heat. Ironically, oils that are less-refined and higher in healthful compounds are the worst choices for high-heat cooking. Here are my top picks for which oils to use.

High heat. Not many healthful oils will stand up to these temperatures. Unrefined avocado oil is sturdy with lots of “good fats.” A refined high-oleic sunflower oil isn’t my top pick because it’s so refined, but it’s better than regular sunflower oil. If you want to cook on high with olive oil, you need a refined “light” olive oil.

Medium-high heat. Heart-healthy virgin olive oil, rich in monounsaturated fat, is a go-to here. So is macadamia nut oil, which is even richer in monos than olive oil. Almond oil, peanut oil and refined hazelnut oil are other good choices.

Low or medium heat (including baking). You can use extra-virgin olive oil (it’s a little less refined than virgin olive oil). Virgin, unrefined coconut oil, which is solid at room temperature, contains “good” saturated fat. Grass-fed butter fits here too, and it’s a source of conjugated linoleic acid (a health-promoting fatty acid.)

No heat. Flaxseed oil is rich in a number of healthful compounds, including essential omega-3 fatty acids. This makes it fragile, so store it in the refrigerator and never heat it. Use it on salads or already-cooked vegetables. Treat healthful hempseed oil and unrefined hazelnut or walnut oils similarly.

Next time: Is vitamin B really an energy source?

Carrie Dennett:

Dennett is a graduate student in the nutritional-sciences program at UW; her blog is