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 in modern society. Back in the day, it was carbohydrates taking the brunt of the blame, then it was dietary fat, then carbohydrates again, and now we have the new kid on the block: seed oils, accompanied by metaphorical cue cards for dramatic music in online wellness spaces.
The term "seed oils" typically refers to common vegetable oils such as sunflower, soybean, and canola oil, all of which are notably high in polyunsaturated fats. By now, anyone spending time on social media or health forums has likely seen a plethora of dramatic claims insisting that these oils are essentially poisonous, and that their regular consumption leads directly to chronic inflammation and every disease known to humankind. But is that really the case when we look closely at the empirical data? Or is this simply another case of a cyclical dietary fear-mongering fad that will eventually fade into obscurity, only to be replaced by a new villain 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% right! Just kidding.
To separate sensationalist social media narratives from actual scientific inquiry, a recent umbrella review looked at an astonishing 48 systematic reviews and meta-analyses to examine the true effect of vegetable oils on multiple critical health outcomes, including blood pressure, blood lipids, blood sugar, body weight, cardiovascular disease, and cancer.
When analyzing the biochemical data, oils rich in monounsaturated and polyunsaturated fats—which include many of the commonly vilified seed oils—generally improved or, at worst, maintained healthy lipid profiles when compared directly to more saturated fats. Looking at specific varieties, canola oil lowered total cholesterol and low-density lipoprotein (LDL) cholesterol, while showing neutral effects on triglycerides and very-low-density lipoprotein (VLDL). Similarly, rice bran oil also demonstrated an ability to lower total cholesterol and LDL cholesterol. Virgin or extra-virgin olive oil—a staple of the Mediterranean diet—lowered total cholesterol, sometimes reduced LDL cholesterol, and often raised high-density lipoprotein (HDL) cholesterol, which is traditionally viewed as beneficial for heart health.
On the other hand, tropical oils like coconut and palm oils consistently raised total cholesterol and LDL cholesterol, although they also tended to raise HDL cholesterol as well, a finding that somewhat muddies the waters for consumers trying to navigate saturated versus unsaturated fat guidelines.
When researchers evaluated outcomes related to blood pressure and glycemic control, some seed oils actually appeared to offer tangible metabolic benefits. Flaxseed oil produced small but meaningful reductions in blood pressure, particularly diastolic blood pressure, a physiological response that researchers suggest may be attributed to its high alpha-linolenic acid (ALA) content. Sesame oil showed modest reductions in blood pressure alongside improvements in fasting glucose and glycated hemoglobin (HbA1c) levels in certain cases. Furthermore, olive oil and even coconut oil produced small, measurable improvements in some glycemic markers as well.
As it pertains to broader health metrics such as systemic inflammation, major cardiovascular events, and cancer incidence, the available data were admittedly limited but did not suggest any increased risk associated with the consumption of these oils. The exact same conclusion applied to body weight and body composition measures, where only very small, clinically insignificant changes were observed across a few studies.
It remains important to contextualize these findings by noting that the overall certainty of evidence across the reviewed literature was mostly low, and culinary oils are rarely consumed entirely in isolation. Additionally, oils used in home cooking under standard domestic conditions differ significantly from those repeatedly reheated at high temperatures, as is often the case in many commercial fast-food restaurant fryers, where thermal degradation can alter the chemical composition of the fat.
Regardless of these variables, the evidence currently available by no means supports the idea that consuming seed oils as part of an otherwise healthy, balanced diet will lead to deleterious health outcomes. On the contrary, in some instances, their inclusion may even lead to marginal physiological improvements. As nutritional scientists have long emphasized, 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 lifestyle context, whether you choose to consume some seed oils in your cooking or not is unlikely to make a massive, noticeable difference to your overall health trajectory.
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