If an effect refers to a Food, it means any Food artifact, not just a Food artifact token. For example, you can sacrifice Tough Cookie (an Artifact Creature — Food Golem) to activate Maraleaf Rider's ability (an ability with "Sacrifice a Food" in its cost).
If the target creature is an illegal target by the time Insatiable Appetite tries to resolve, the spell won't resolve. You won't sacrifice a Food.
You choose a target creature as you cast Insatiable Appetite, but you don't choose whether to sacrifice a Food until the spell resolves.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Nils Hamm
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