Britannica Sources used in this answer

Why do trans-fat molecules have a more linear shape than cis unsaturated fats?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Trans fat Commercially manufactured foods, including cookies, doughnuts, and muffins, often contain trans fats.

The difference in shape between cis and trans unsaturated fats is determined by the orientation of the hydrocarbon chains around the double bond. Because double bonds prevent free rotation, they impart rigidity to the molecule, locking the adjacent groups into specific positions.12

In a cis configuration, the hydrocarbon chains connected to the double-bonded carbons lie on the same side of the molecule. This creates a "v" shape or a bend at the site of the double bond.34

In contrast, the trans configuration—often produced through the industrial process of hydrogenation—places the hydrocarbon chains on opposite sides of the double bond. This arrangement results in a single twist in the center of the molecule, which effectively straightens the chain. Consequently, the trans fat molecule adopts a linear structure that closely resembles the shape of a saturated fat.34