The belief that vegetable oil is heart-healthy rests substantially on early data that was confounded (muddied by other factors). The trials done since have not been kind to it.
Where the confounding came in
Older data was confounded because it lumped omega-3 polyunsaturated fatty acid intake in with omega-6. That mix misrepresented the health benefits of omega-6 specifically. Other work found that omega-6 PUFA increased death and coronary heart disease compared with animal fat. That work includes the Anti-Coronary Club trial.
A meta-analysis of almost 10,000 patients confirmed it. 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 (brain and mood problems). This includes 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 (blood) saturated fatty acids from dairy sources such as cheese and yogurt are inversely related to the incidence of type 2 diabetes. That means more of them goes with fewer new cases.
Neuroinflammation, mood and attention
Processed food, and specifically where its fat comes from, is associated with several neuropsychiatric conditions — neuroinflammation, anxiety, depression and attention disorders among them. The fat in processed food is mostly industrial seed oil. That 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 type 2 diabetes patient who did not have all three. The root cause of the obesity, prediabetes and type 2 diabetes epidemic is that combination. It is acellular carbohydrate, industrial seed oil and refined grain, arriving together in nearly everything ultra-processed.
Related reading
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed August 25, 2026
