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How does hydrogenation change unsaturated vegetable oils into more solid fats?

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Synthesis of palmitate — Fat Palmitic acid is one of the most prevalent fatty acids occurring in the oils and fats of animals; it also occurs naturally in palm oil. It is generated through the addition of an acetyl group to multiple malonyl groups connected by single bonds between carbons. This structure forms a saturated acid—a major component of solid glycerides.

Hydrogenation is a chemical process used to convert liquid vegetable oils into more solid, stable fats by adding hydrogen to the double bonds of unsaturated fatty acids.12

This process typically occurs in a pressure vessel where the oil is treated with a catalyst—often finely divided nickel—at high temperatures and pressures. By saturating these double bonds, the fatty acids become more stable and resistant to oxidation, resulting in a product that is more solid and spreadable at room temperature, such as margarine or shortening.312

Additionally, the process triggers isomerization, where some unsaturated fatty acids shift from their natural cis configuration to a trans configuration. These trans isomers have higher melting points than the original cis forms, further contributing to the hardening of the oil. Because these trans-fatty acids behave similarly to saturated fats, they can have negative implications for health.42