  We perform a Nf = 2 + 1 lattice QCD simulation to determine the quark spin
fractions of hadrons using the Feynman-Hellmann theorem. By introducing an
external spin operator to the fermion action, the matrix elements relevant for
quark spin fractions are extracted from the linear response of the hadron
energies. Simulations indicate that the Feynman-Hellmann method offers
statistical precision that is comparable to the standard three-point function
approach, with the added benefit that it is less susceptible to excited state
contamination. This suggests that the Feynman-Hellmann technique offers a
promising alternative for calculations of quark line disconnected contributions
to hadronic matrix elements. At the SU(3)-flavour symmetry point, we find that
the connected quark spin fractions are universally in the range 55-70% for
vector mesons and octet and decuplet baryons. There is an indication that the
amount of spin suppression is quite sensitive to the strength of SU(3)
breaking.
