Space Marines can eat anything. Even their own recycled waste! But there was the original Space Marine novel, that had neophytes taking part in a banquet of exotic foods. Spoiler That included a dish made with Human meat! And considering how long SM live, if they make a sandwich it will either be wholely utilitarian or made to a high standard out of ingredients that can have lethal consequences for an un-enhanced human! It is a reference to how Astartes food usually has additives in it for their system. Like the minerals and ceramic-based substances to increase the strength of their bones. Though I am unsure whether these additives are actually toxic to humans? At least in the quantities full battle-brothers are required to consume.
