The 8 Least Healthy Vegetable Oils, According To An MD

Butter is not always high on the list of health foods, but is it healthier than most vegetable oils? According to family physician and New York Times bestselling author Cate Shanahan, M.D., the answer is a resounding yes. 

During a mindbodygreen podcast episode, Shanahan says, "I think vegetable oils are the No. 1 cause of health problems in this country." Now, before anyone starts throwing away their cooking oils, Shanahan is only referring to eight specific types of vegetable oils. 

Eight of the most unhealthy vegetable oils, according to Shanahan, include:

These oils are deemed unhealthy by Shanahan for two reasons: They're highly refined, and they're high in polyunsaturated fatty acids (PUFA).

Though polyunsaturated fats are actually healthier than saturated and trans fats, (and have been shown to reduce "bad" or LDL1 cholesterol), Shanahan says they're highly unstable. Meaning, when they're exposed to chemicals in the refining process, they're stripped of their antioxidants, vitamins, and minerals. Over time, PUFA becomes stored in the body fat, which may lead to inflammation2.

Seeds, nuts, beans, fruit, dairy, and animal fats are all naturally derived and healthy to eat. Those are all good, Shanahan says, so the question becomes: What kind of added fats are safe?

"For all foods, we have to consider the nature of the fats," Shanahan says. Traditional added fats, like butter, are closer to whole foods than refined oils are. "You don't need high heat, you don't need complicated equipment, you don't need refining machinery," Shanahan says about butter. "You just let the cream rise to the top, skim it off, and then you start churning it around, and that's butter."

The same can be said of olive oil, coconut oil, and avocado oil when they're cold-pressed and unrefined. Traditionally, these oils are squeezed straight from the fruit, or the seed of the fruit, and are not stripped of their antioxidants and minerals. 

Not all fats or cooking oils are unhealthy. In fact, in their natural and unrefined state, fats can be healthy. When possible, Shanahan recommends avoiding or limiting these eight oils: corn, canola, cottonseed, soy, safflower, sunflower, grapeseed, and rice bran oils, which may lead to inflammation over time.