Butter, olive oil and your body fat share one simple molecular shape
Almost every fat you eat or store is a triglyceride: one glycerol backbone with three fatty acid tails attached. Whether it sits as a solid block of lard or pours as olive oil depends mostly on how many carbon double bonds those tails carry, and the same chemistry turns linseed oil into hard paint.
Chemically a triglyceride is an ester, formed when glycerol condenses with three fatty acids and gives off three molecules of water. The three tails are usually different, and chemists label their positions sn-1, sn-2 and sn-3. If all three differ, the molecule becomes chiral. Long-chain versions carry fatty acids of 16, 18 or 20 carbons. Animals build only even-numbered chains, but bacteria can make odd and branched ones, which is why fat from cattle and other ruminants contains odd chains such as 15 carbons, courtesy of microbes in the rumen.
Saturated tails have no carbon double bonds; unsaturated ones have at least one. Double bonds lower the melting point, so tallow and lard stay solid while olive and linseed oils flow. The trade-off is that unsaturated fats react with air and turn rancid, a vulnerability that grows with each extra double bond and that antioxidants can slow. Industry's workaround is hydrogenation: a catalyst adds hydrogen across the double bonds, turning vegetable oil into margarine that resists spoiling, though the process can also create unwanted trans acids.
Nature does not assemble these molecules at random. Enzymes attach specific acids to specific positions, and in most vegetable oils the saturated tails sit at the ends while an unsaturated one takes the middle. Cocoa butter is a striking case, made from only a handful of triglycerides, which helps explain why it melts so neatly, whereas most fats are messy blends that soften over a wide range of temperatures. Even olive oil varies, its oleic acid share ranging from 64 to 86 percent.
Energy content drops slightly as unsaturation rises, by roughly 0.6 percent per double bond. In the body, triglycerides form most stored fat and much of skin oil, and they circulate in blood to shuttle fat and glucose to and from the liver.
Source: Triglyceride
