Source: The Impossible Eye, pg(s). 88-89
Nephilim typically eat much more than humans do, but are hardy enough to subsist on a typical human's diet when food is scarce. They can live up to 600 years. Nephilim can breed with humans to produce half-nephilim offspring, who are nearly identical to humans but are all large, strong, and long-lived.
Since nephilim span the sacred line between mortals and immortals, they were cursed and hunted down by both mortals and gods. Over the years, most nephilim have been wiped out, but a small population remains and has kept their number steady (if not increasing). Most mortals feel intimidated by or hostile to nephilim, who are aware of this and tend to keep to themselves in wild or abandoned places, only occasionally allying with and serving as mercenaries to local rulers.