Is Your Cooking Oil Releasing Toxic Chemicals?

Even if you think you're using healthy oils when you cook, you could be doing damage to your body: Cooking certain oils at too high of a heat releases high levels of toxic chemicals linked to cancer, heart disease, and dementia, according to a new study from the U.K.

Researchers found that when fish and chips were fried in either corn or sunflower oil, the food contained up to 200 times more of the toxic chemical aldehyde-which has been linked with most major diseases-than what is considered safe. Olive oil, butter, and coconut oil on the other hand, yielded far lower (and completely safe) levels of aldehyde.

"High-heat cooking begins to oxidize oils, which not only changes the taste of the food, but alters the nutritional and chemical component of the oils," explains Manuel Villacorta, R.D, author of Whole Body Reboot: The Peruvian Superfoods Diet to Detoxify, Energize, and Supercharge Fat Loss, who was not involved in the study.

Unfortunately, there's no standard smoke point-the temperature at which oil begins to oxidize-for all oils. So how can you make sure you're not frying up the wrong one and leeching toxins into your dinner? Check out the best way to use four of our favorite oils. (Or try 8 New Healthy Oils to Cook With.)

Avocado Oil

Health Perks: Extracted from the flesh of the avocado, this oil is high in oleic acid, a monounsaturated omega-9 fatty acid; powerful phytonutrients like beta-sitosterol, which have been shown to lower cholesterol; and glutathione, which provides protection against certain types of cancer, Villacorta says.

Smoke Point: 375 to 400°F

Best For: Because it stands up to heat so well, avocado oil is great for grilling or baking vegetables. Off the heat, Villacorta loves the mild, nutty, and natural buttery taste in salads, salsas, fish marinades, and bread dips.

Canola Oil

Health Perks: Canola oil is high in oleic acid-and therefore monounsaturated fat-and is also the lowest in saturated fat of any common cooking oil. Together, these fat levels mean canola is great for your heart and one of the healthiest edible vegetable oils, Villacorta explains.

Smoke Point 468°F

Best For: With one of the highest heat tolerances of any cooking oil-plus its healthy fat profile, light texture, and neutral flavor-canola oil is ideal for super high-heat cooking, like frying or browning meat.

Olive Oil

Health Perks: Olive oil is the poster child for healthy oils-and rightly so. The antioxidants in it help reduce inflammation and improve insulin sensitivity, which stabilizes your blood sugar. The high concentrations of monounsaturated fat helps to lower "bad" (LDL) cholesterol, increase "good" (HDL) cholesterol, provide sustained blood sugar control, and keep your heart healthy, Villacorta adds. (Find out more benefits: Is Olive Oil Better Than We Ever Thought?)

Smoke Point: 365 to 400ºF

Best For: Pure extra virgin olive oil is best used raw, as in dressings, drizzles, or dips, but it can also be used at lower cooking temperatures, like to sauté vegetables, he suggests.

Coconut Oil

Health Perks: Derived from the flesh of coconut meat, coconut oil has long been used to promote good heath (along with healthy hair and skin). Plus, it has more beneficial triglycerides, which are the lipids found in your blood as a result of the calories your body doesn't burn right away. While most oils contain high levels of long-chain triglycerides, coconut contains a high percentage of medium-chain triglycerides (MCTs) which are more easily utilized as fuel with less effort from your body, thereby promoting weight loss, Villacorta explains. Research also shows that coconut oil helps keep your cholesterol levels healthy and reduce oxidative stress and combat free radical damage via the powerful antioxidants vitamin E and polyphenols.

Smoke Point: 350°F

Best For: Its lower smoke point and natural sweetness makes coconut oil a great choice for baking, particularly as a substitute for butter. (Need a place to start? Try one of 10 Tasty Coconut Oil Recipes.)