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, accompanied by metaphorical cue cards for dramatic music.
The term “seed oils” usually refers to common vegetable oils like sunflower, soybean, and canola, which are high in polyunsaturated fats. By now, anyone following health and wellness trends online has likely seen a plethora of claims about seed oils, how they are supposedly poisonous, and that all they are good for is promoting systemic inflammation and every disease known to man. But is that really the case when we look closely at the data? Or is this simply another case of a dietary fear-mongering fad that will eventually 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 internet influencers who claimed so were 100 percent right!
Just kidding.
A recent umbrella review, which looked at an astonishing 48 systematic reviews and meta-analyses, has examined the effect of vegetable oils on multiple critical health outcomes, including blood pressure, blood lipids, blood sugar, body weight, cardiovascular disease, and cancer. The findings offer a much-needed breath of fresh air and empirical grounding in a landscape often dominated by sensationalized headlines and nutritional anxiety.
Looking closely at the metabolic effects, oils rich in monounsaturated and polyunsaturated fats, which include many common seed oils, generally improved or, at the absolute worst, maintained healthy lipid profiles when compared to more saturated fats. Canola oil, for instance, demonstrated an ability to lower total cholesterol and low-density lipoprotein, commonly known as LDL, while showing neutral effects on triglycerides and very-low-density lipoproteins. Similarly, rice bran oil also showed efficacy in lowering total cholesterol and LDL.
When looking at virgin or extra-virgin olive oil—deserving of a special shoutout to Greece—the data showed it lowered total cholesterol, sometimes reduced LDL, and frequently raised high-density lipoprotein, or HDL, which is traditionally viewed as the beneficial form of cholesterol. On the other hand, coconut and palm oils consistently raised total cholesterol and LDL, although they also tended to raise HDL as well, a finding that somewhat muddies the waters regarding their overall cardiovascular classification.
When it comes to blood pressure and glycemic control, some seed oils actually appeared to be genuinely beneficial. Flaxseed oil produced small but meaningful reductions in blood pressure, especially diastolic pressure, a phenomenon researchers believe may be connected to its high alpha-linolenic acid content, known as ALA. Sesame oil also showed modest reductions in blood pressure and notable improvements in fasting glucose and HbA1c levels in certain cases, while olive oil and even coconut oil produced small improvements in some glycemic markers as well.
As it pertains to inflammation, cardiovascular events, and cancer, the available data were somewhat limited but by no means suggested an increased risk from consuming these oils. The exact same conclusion was found for body weight and body composition measures, where only very small and clinically insignificant changes were observed across a few studies.
It remains important to note, however, that the overall certainty of evidence across these reviews was mostly low, and oils are typically not consumed in isolation by human beings. Additionally, oils used in home cooking under normal circumstances differ significantly from those repeatedly reheated at high temperatures, as is often the case in many commercial fast-food restaurant fryers, which can alter the chemical composition and degradation products of the fats.
Regardless of these nuances, the evidence we currently have by no means supports the idea that consuming seed oils as part of an otherwise healthy, balanced diet will lead to deleterious health outcomes. In fact, in some cases, incorporating them may even lead to marginal health improvements. As is almost always the case in nutritional science, managing your overall energy intake and doing your best to consume mostly whole, minimally processed foods is what truly matters for long-term health and well-being. In that broader context, whether you choose to consume some seed oils or not is unlikely to make a huge difference to your overall health trajectory.
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