  We study the nature of the triadic interactions in Fourier space for
three-dimensional Navier-Stokes equations based on the helicity content of the
participating modes. Using the tool of helical Fourier decomposition we are
able to access the effects of a group of triads on the energy cascade process
and on the small-scale intermittency. We show that while triadic interactions
involving modes with only one sign of helicity results to an inverse cascade of
energy and to a complete depletion of the intermittency, absence of such
triadic interactions has no visible effect on the energy cascade and on the
inertial-range intermittency of the three-dimensional Navier-Stokes equations.
