Cooking With Oils

In his letter, Edward J. Behrman indicates that thermal isomerization of olefins can play a role in the cis- versus trans-fat content in cooking oils and suggests that cooking with oils with no trans fat may not eliminate them from the diet (C&EN, Feb. 3, page 2). My recollection from organic chemistry is that thermal isomerization without the help of some catalyst would cause more degradation than isomerization.

Regardless, in an article titled “Heat Induced Cis/Trans Isomerization in Vegetable Oils and Oleic Acid” by John-Harwood Scott and Sarah E. G. Porter, they write: “The results indicate that heating canola, corn, and premium and generic olive oil to their smoke point for at least 15 minutes does not quantifiably increase their respective concentration of trans fatty acids” (http://blogs.longwood.edu/incite/2012/01/30/heat-induced-cistrans-isomerization-in-vegetable-oils-and-oleic-acid).

Cooking is typically not done near the smoke point of the oils because the taste of the food is dramatically diminished and it poses a fire hazard. So the health risk from a fire at those temperatures is probably much worse than any amount of trans fat that may occur and be ingested by consuming cooked oils.

Steve L. Aprahamian
Pittsburgh