What does the research say about seed oils and chronic disease?

Large-scale epidemiological evidence, reviewed by institutions including Harvard T.H. Chan School of Public Health and Stanford Medicine, consistently links higher polyunsaturated fat (PUFA) intake — including from seed oils — to lower rates of cardiovascular disease and type 2 diabetes, not higher rates. Harvard nutrition professor Walter Willett has noted that the idea of omega-6 fatty acids being pro-inflammatory is "propagated over and over again in social media," but that dozens of studies have examined this and found no supporting evidence in humans.

The biological mechanism most often cited — that omega-6 fatty acids produce arachidonic acid, which in turn produces pro-inflammatory mediators — does not translate into measurable chronic inflammation in human clinical trials. A systematic review published on PubMed found "virtually no evidence" from randomized controlled trials showing that adding linoleic acid to the diet increases concentrations of inflammatory markers in healthy adults.

The Academy of Nutrition and Dietetics cites two separate systematic reviews of RCTs confirming that higher linoleic acid intake had no effect on inflammatory markers. The claim that seed oils cause chronic disease relies on a mechanistic fallacy that breaks down when tested in actual human subjects, and is not supported by the weight of clinical or epidemiological evidence.