Observations of the vicinity of a variety of galactic gamma-ray sources have indicated a local suppression of diffusivity of cosmic rays (CRs) by up to three orders of magnitude. However, the impact of these low-diffusion zones on global properties of CR transport is, however, only poorly understood. Here, we argue that CR nuclear ratios, like the boron-to-carbon ratio and relative abundances of Beryllium isotopes are sensitive to the filling fraction of such low-diffusion zones and hence their measurements can be used to constrain the typical sizes and ages of such regions. We have performed a careful parameter study of a CR transport model that allows for different diffusion coefficients κかっぱ_disc and κかっぱ_halo in the galactic disc and halo, respectively. Making use of preliminary data from the AMS-02 experiment on the ratio of Beryllium isotopes, we find a 3.5σしぐま preference for a suppression of the diffusion coefficient in the disc with a best-fitting value of . We forecast that with upcoming data from the HELIX balloon experiment, the significance could increase to 6.8σしぐま. Adopting a coarse-graining approach, we find that such a strong suppression could be realized if the filling fraction of low-diffusion zones in the disc was . We conclude that the impact of regions of suppressed diffusion might be larger than usually assumed and ought to be taken into account in models of Galactic CR transport.