Molecular modeling of lipids has been hampered by the size of these complex, biologically important molecules. Yet, understanding the structure and energy (enthalpy) of large molecules is critical to identifying their function in chemical equilibrium and transition state theory. In this work, we use both experimental data and G4 computed results, to show that cis polyunsaturated lipids have helical conformers. We present linear functions for the enthalpy of formation ΔfH°298 and the Gibbs free energy of formation ΔfG°298 as a function of n, where n is the number of carbon atoms in a linear carboxylic acid chain. Taking ΔfH°298 of a saturated acid as a starting point, we add the enthalpy of hydrogenation ΔhydH°298 at appropriate locations on the carbon chain to model polyunsaturated fatty acids. For example, taking eicosanoic acid (C20) as a saturated starting point, we add four enthalpies of cis-dehydrogenation (ΔhydH°298) to obtain arachidonic acid (eicosa-5Z,8Z,11Z,14Z-tetraenoic acid). We compare Gaussian-4 computational results, to show evidence of helical structure. We conclude that fatty acids can have helical conformers facilitating a broad range of biological functions. Keywords: G4 Calculations, Helix, Lipid, Molecular Structure, Thermochemistry