The belief that vegetable oil is heart-healthy rests substantially on early data that was confounded, and the trials conducted since have not been kind to it.
Where the confounding came in
Older data was confounded by including omega-3 polyunsaturated fatty acid intake alongside omega-6. That inclusion misrepresented the health benefits attributable to omega-6 specifically. Other work, including the Anti-Coronary Club trial, found that omega-6 PUFA increased death and coronary heart disease compared with animal fat.
A meta-analysis including almost 10,000 patients confirmed that high intake of omega-6 oils from vegetable oils and margarines increases the risk of death and heart disease compared with saturated fat.
The ratio
The Standard American Diet has a greater than 20:1 ratio of omega-6 to omega-3. That distortion is associated with a range of neuropsychiatric dysfunction, including profound anxiety. Restoring a healthier ratio nearer 4:1 — even by supplementing omega-3 rather than removing omega-6 — appears to reduce that anxiety. (Buydens-Branchey L, Branchey M, 2007.)
Seed oil and type 2 diabetes
Processed seed oil is associated with type 2 diabetes. In the opposite direction, cohort studies find that plasma saturated fatty acids from dairy sources such as cheese and yoghurt are inversely related to the incidence of type 2 diabetes.
Neuroinflammation, mood and attention
Processed food, and specifically the origin of its fat content, is associated with several neuropsychiatric conditions — neuroinflammation, anxiety, depression and attention disorders among them. The fat in processed food is predominantly industrial seed oil, which is what makes this more than a correlation with processed food in general.
The unholy trifecta
Sugar, vegetable oil and grain. In more than twenty years of practice I have not seen a patient with type 2 diabetes who did not have all three. The root cause of the obesity, prediabetes and type 2 diabetes epidemic is that combination: acellular carbohydrate, industrial seed oil and refined grain, arriving together in nearly everything ultra-processed.
