Branching by double bonds
Fatty acids are chains of carbon atoms, and the primary branch point is how many carbon-to-carbon double bonds they contain. Saturated fatty acids have none, so the chain is straight and packs tightly, which is why they tend to be solid at room temperature. Monounsaturated fatty acids have one double bond, and polyunsaturated fatty acids have two or more; each double bond introduces a kink that lowers the melting point and tends to make the fat liquid.
Trans fats are a separate branch: usually industrially produced unsaturated fats whose double bond is in the trans configuration, giving them a straighter shape that behaves more like a saturated fat.
Chain length and double-bond position
Beyond saturation, fatty acids also differ by chain length, from short to long, which affects how they are absorbed and used, and by where the first double bond sits, which defines families such as omega-3 and omega-6. These structural details, not just the saturated-versus-unsaturated label, drive how a fat behaves in the body.
Industrial trans fats are widely recognised as harmful to cardiovascular health and have been restricted in many countries. This is general educational information about fat chemistry, not dietary advice; consult a qualified professional for personal guidance.