Seed Oils’ Impact on Health

After over a half century of public health advice warning against diets high in saturated fat, the finger is starting to point toward oils rich in polyunsaturated fatty acids (PUFAs) as contributing factors in a range of adverse health outcomes. A paper published recently in Frontiers in Nutrition introduces a theory that puts refined, bleached, and deodorized (RBD) seed oils at center stage as causative agents in cancer and metabolic disease (insulin resistance and its sequelae). 

The oils implicated include highly processed oils, such as soybean, corn, canola, cottonseed, sunflower, and safflower oils. The author makes the case that high consumption of these oils leads to greater deposition of PUFAs in body fat and mitochondrial membranes, and this undesirable composition of membrane fatty acids leads to oxidative damage and mitochondrial dysfunction, which ultimately results in insulin resistance and an over-reliance on glucose for fuel (owing to reduced capacity to oxidize fatty acids)—a hallmark of the Warburg effect, associated with cancer cells’ insatiable appetite for glucose. 

Excessive intakes of sugar and refined carbohydrates typically take the blame for the rising incidence of type 2 diabetes and prediabetes, but this paper presented data showing a stronger correlation between per capita RBD seed oil consumption and incidence of these conditions in the US over the past sixty years. The author notes that RBD seed oils now account for 80 percent of the average American’s fat intake, and this is reflected in the composition of body fat: the percentage of linoleic acid in human adipose tissue doubled between 1955 and 2008. This evolutionarily novel change may have profound implications for our health, possibly leading to the following cascade proposed by the author: 

1. Replacing animal fats with RBD seed oil promotes cellular oxidative stress.
2. High seed oil diets produce high PUFA body fat and harm mitochondria.
3. Mitochondrial adaptation to increased oxidative stress may involve increased aerobic glycolysis.
4. Increased aerobic glycolysis profoundly disrupts glucose homeostasis, leading to insulin resistance. 

Previous research suggested that seed oils rich in PUFAs are much more plausible contributors to heart disease compared to saturated fats. This new paper suggests that these supposedly “heart healthy” oils may be increasing risk for type 2 diabetes and cancer as well.