Are “seed oils” actually unhealthy? • Stronger by Science

There must always be a nutritional “bad guy” –a macronutrient or ingredient that is vilified and presented as the main culprit behind bad health outcomes. Back in the day, it was carbs, then it was fat, then carbs again, and now we have the new kid on the block … seed oils *cue dramatic music.*

The term “seed oils” usually refers to vegetable oils like sunflower, soybean, and canola, which are high in polyunsaturated fats. By now, I’m sure that you’ve seen a plethora of claims about seed oils, how they’re poisonous, and that all they’re good for is inflammation and every disease known to man. But is that really the case when we look at the data? Or is this another case of a dietary fear-mongering fad that will fade and be replaced by something else in a few months?

We all know the answer here.

Turns out, seed oils are indeed the worst, and all those who claimed so were 100% right!

Just kidding.

A recent umbrella review, which looked at 48 systematic reviews and meta-analyses (!), examined the effect of vegetable oils on multiple health outcomes, including blood pressure, blood lipids, blood sugar, body weight, cardiovascular disease, and cancer. 

Oils rich in monounsaturated and polyunsaturated fats, which include many seed oils, generally improved or, at worst, maintained healthy lipid profiles when compared to more saturated fats. Canola oil lowered total cholesterol and LDL, with neutral effects on triglycerides and VLDL, while rice bran oil also lowered total cholesterol and LDL. Virgin or extra-virgin olive oil (shoutout Greece) lowered total cholesterol, sometimes reduced LDL, and often raised HDL. On the other hand, coconut and palm oils consistently raised total cholesterol and LDL, although they also tended to raise HDL, a finding that somewhat muddies the waters. 

When it comes to blood pressure and glycemic control, some seed oils actually appeared to be beneficial, with flaxseed oil producing small but meaningful reductions in blood pressure, especially diastolic pressure, possibly because of its high ALA content. Sesame oil showed modest reductions in blood pressure and improvements in fasting glucose and HbA1c in some cases, while olive oil and even coconut oil also produced small improvements in some glycaemic markers. 

As it pertains to inflammation, cardiovascular events, and cancer, data were limited but did not suggest increased risk. The same was true for body weight and body composition measures, where only very small changes were observed in a few studies.

It’s important to note that the overall certainty of evidence was mostly low, and oils are usually not consumed in isolation. Additionally, oils used in home cooking differ from those repeatedly reheated, as in many fast-food restaurant fryers. 

Regardless, the evidence we currently have by no means supports the idea that consuming seed oils as part of a healthy diet will lead to deleterious health outcomes, and in some cases, it may even lead to marginal improvements. As always, managing your overall energy intake and doing your best to consume mostly whole foods is what’s important. In that context, whether you consume some seed oils or not is unlikely to make a huge difference to your health.