Another problem was that some seeds and carbohydrate sources are poisonous . Cyanogenic glycosides , which can be found in linseed , cassava , and manioc , amongst others , are made non-poisonous through cooking . The incorporation of toxins into the seeds and similar carbohydrate sources also affected the diet , as cyanogenic glycosides such as those found in linseed , cassava , and manioc are made non-toxic through cooking .