Provided are: method of producing a sulfur-containing proanthocyanidin
oligomer by reducing the molecular weight of proanthocyanidin in plants
so that they can be readily absorbed through the intestine of an
organism; and a health food composition and a pharmaceutical composition
which contain the resultant sulfur-containing proanthocyanidin oligomer
as an active ingredient and which are useful for treating and preventing
various lifestyle-related diseases and brain diseases caused by
generation of active oxygen species as well as for preventing aging.