In 1999, Meléndez et al claimed that the structure of glycogen is optimal under a particular metabolic constraint model, where the structure was suggested to be "fractal" in nature. However, research by Besford et al used small angle X-ray scattering experiments accompanied by branching theory models to show that glycogen is a randomly hyperbranched polymer nanoparticle. Glycogen is not fractal in nature. This has been subsequently verified by others who have performed Monte Carlo simulations of glycogen particle growth, and shown that the molecular density reaches a maximum near the centre of the nanoparticle structure, not at the periphery (contradicting a fractal structure that would have greater density at the periphery).