The phrase "certain foodstuffs" means specific types of food or ingredients. It refers to particular kinds of food rather than all types of food. Full definition
This is probably due to hormonal changes, but could be indicative of a mineral shortage which the body tries to rectify by making certain foodstuffs (or non-foodstuffs) that contains this mineral, attractive to eat. (wehavekids.com)
These profiles may not be adequate in all cases since they, in turn, were developed from National Research Council guidelines, which assume complete bioavailability of the nutrients and leave no margin of error for breed differences, impaired absorption, reduced digestibility of certain foodstuffs, or changes in animal physiology in certain disease states. (cedarbayouanimalclinic.com)
I recalled the Wartime Foods allocations, called, appropriately — rations, (where rich and poor were treated alike here in Canada), and only permitted to buy certain foodstuffs, and only in basic controlled amounts through specific monitored timelines. (remonline.com)