Lipids are composed of repeating fatty acid units, and we need a certain percentage of dietary fat and oil intake to sustain optimal health. The physical state of fat depends on both the length of the carbon chain and the hydrogen saturation level. Lengthier fatty acid chains that are saturated with hydrogen atoms and have single bonds between carbons tend to be solid at room temperature, and are usually called fats. Oils tend to have smaller fatty acid chains, and be unsaturated (containing double or triple bonds between carbons), and are usually liquid at room temperature. Trans fats are a type of unsaturated fat which has a “trans” (opposite) configuration on each side of the double bond as opposed to a “cis” (same side). We’ll come back to trans fats in a bit.