Something else I want to mention is that I'm pretty sure that flood can't starve once they get a host seeing as between Halo 2 and Halo 3 they literally transformed high charity from this. https://content.halocdn.com/media/Default/encyclopedia/locations/high-charity/high-charity-thumbnail-708x398-bbdb0d86bcb947fbbb3da17850cbea2f.jpg To this http://static3.wikia.nocookie.net/__cb20080529200237/halo/images/2/2c/Flood_Charity.png And even inside it looked like this https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQTLFE-RsWtdgyLZlZLK3xVEdCHLchaj75J5B1G0p5VJq3qhHfhvw This would require more biomass then was actually in high charity, and as far as we know they never had a chance to get more. So this shows that the Flood can create more bio mass. Another showing was when they created a spore mountain. “The object rises fifty kilometers above the planet’s datum and measures four hundred kilometers across the base, at its greatest diameter. It intersects many Forerunner constructs and appears to have arisen at the center of a major city, which city is, if memory serves— if this is truly Uthera—” Bear, Greg (2013-03-19). Halo: Silentium (Forerunner) (p. 82). Tom Doherty Associates. Kindle Edition. (Note I know it doesn't reference it as a Flood construct but you can check page 82 of Silentium to see) This shows that the Flood have they ability to create biomass. Also of note is that the Flood were quarantined to 12 systems for 290 years by the Forerunners, whenever they escaped to another system the Forerunners would detonate the systems sun. If the Flood could still starve, they would have at this point.