  We study a twist decomposition of diffractive structure functions in the
diffractive deep inelastic scattering (DDIS) at HERA. At low Q2 and at large
energy the data exhibit a strong excess, up to about 100%, above the twist 2
NLO DGLAP description. The excess in consistent with higher twist effects. It
is found, that complementing the DGLAP fit by twist 4 and 6 components of the
GBW saturation model leads to a good description of data at low Q2. We conclude
that the DDIS at HERA provides the first, strong evidence of higher twist
effects in DIS.
