Isolated pulsars are rotating neutron stars with accurately measured angular velocities Omega, and their time derivatives that show unambiguously that the pulsars are slowing down. Although the exact mechanism of the spin-down is a question of detailed debate, the commonly accepted view is that it arises through emission of magnetic dipole radiation (MDR) from a rotating magnetized body. The calculated energy loss by a rotating pulsar with a constant moment of inertia is assumed proportional to a modeldependent power of Omega. This relation leads to the power law (Omega) over dot = -K Omega^n where n is called the braking index. The aim of this work is to determine the deviation of the value of n from the canonical n = 3 for a star with a frequency dependent moment of inertia in the region of frequencies from zero (static spherical star) to the Kepler velocity (onset of mass shedding by a rotating deformed star), in the macroscopic MDR model. We use microscopic realistic equations of