If starvation was a very big part of your setting, how would you model crunch to reflect that?  I would like starvation to primarily serve the purpose of spurring the players onwards towards desperation and perhaps even looting if others will not part with their blessings.

Would you model this in some kind of persistent crunch or just choose to apply penalty dice to certain activities if it's been awhile since they've eaten?  I suppose I could have them battle an effect by acquiring sustenance but it would seem quite lame to intermittently have the affect re-appear.  Thoughts?

If starvation were just one of many things in the setting and not the most important thing, then I'd probably go with the standard rules - no overhead in normal situations, but when the SG decides that food has become an issue, allow the characters opportunities to resolve it with different sorts of conflicts. The stakes at hand might concern anything from whether the characters will be weakened by hunger (Harm) to death or illness of secondary characters to outright death by starvation.

Doing it like above allows you to control the pace of the issue. In one scene you remind the players that supplies are running out, then in another one you tell them that they're out of food and will have to start fasting if nothing is resolved. The next time they'll start getting penalty dice for being weak from hunger and then you can start asking for annoying Endurance checks like "let's see if you're buff enough to crawl your way to that city in your weakened condition". Ultimately it will be no surprise to anybody when you lay down the extreme situations like "let's roll the dice to see which one of you guys is going to expire first".

Of course, through that arc you'd most likely offer different potential solutions to the problem, such as the characters selling themselves as slaves to some lizard people or whatever your genre's about. And if the characters prove ineffective on procuring food, you can turn these failures into Harm, which will then make the characters less effective in achieving anything else, either. Should the players simply not care about doing something to the starvation, it'll be a cruel and short life for their characters. Unless the situation requires the SG to do some dramatic coordination to save them despite their own failure to address the situation.

In summation, I handle food exactly the same as oxygen - normally it's not a problem, but when the situation says that it is, we use the normal rules to find out what happens. Should the setting be one where starvation is a constant threat, I'd reflect this with a teeny tiny slice of specific crunch. To wit:

Foraging (I)
Most citizens of the soon-to-be-starved-empire have learned to eke out a meager living out of digging for roots and collecting berries in the temperate woodlands near the once-magnificent cities. This is considered primarily women's work, but men go to it when they have to, even if it takes them longer and they might not recognize all food plants so well.

A range of different food-procuring Abilities can then be used to resolve those conflicts, such as whether a character happens to find food or not. You could even have an Ability for storing food:

Hoarding (R)
The primitives of the so-very-hungry-land are usually a short-sighted lot, but some special individuals understand to plan ahead. This Ability can be used to preserve food correctly, figure out how much to eat per day to make it last until the spring and secrete it away so that the barbarians can't find it. Obviously enough, a successful steadholder will need to have some inkling of these skills.

Alternatively, if you wanted to strike a real rift between the rich and the poor:

Secret of Full Belly
The character belongs in a fraternity that, generally speaking, does not starve on a routine basis. He is usually well-fed and gains a bonus die to any Ability checks related to health. As long as the organization itself is preserved intact and the character stays obedient, he does not have to worry about outright starving to death, even if he can't forage for himself.

Interesting, thanks for the response Euro.  I had not thought of having full blown conflicts which inflict Harm, could be somewhat elegant if used sparingly and clearly proliferated in the fiction.

We actually have a Survival ability which includes foraging and basic survival techniques.  Likewise, I'm not sure my players would be interested in Hoarding as an ability but I do kind of like the color.  The Secret is slick as well.  Will definitely have to run these by them.

Oh, the Harm thing should ideally be a standard part of your toolbox as the SG. It's one of my own weaknesses that I don't use Harm enough as a consequence in normal conflicts, but I've been working to improve. It should really be a routine step in your stakes determination - if the conflict actually, factually impacts the character's well-being in the fiction, reflect this by setting a suitable Harm consequence as well.

I'm tempted to use Effects to model all manners of environmental circumstances. That reminds me as an SG that I can use these to either hand out penalty dice or do some damage; in a limited way – repeating a certain environmental and thus faceless threat gets boring, and if the Effect is reduced to zero, it's importance for the story at hand has probably outlived it's usefulness anyway.

A step further would be to have 'Threats as Characters' such as

Draught
Pools
Vigor: 4
Instinct: 0
Reason: 0
Abilities
Starve(V) 2
Infect(V) 2
Kill(V) 1

Notes: Characters may be limited in their ways to attack the Draught. The Draught of course is able to chain abilities to get bonus dice for starving, infecting and killing. If could also generate "Starved" and "Infected" Effects which affect a group of people …

This may be a bit too abstract for some groups, but writing down elements of the game like this moves them out of full-fiat mode for me.

Wow Harald that's hot.  Would the Draught refresh its pool when the PC's refreshed theirs?

That depends on how resilient you want the threat to be.

Basically, the question on NPCs refreshing Pools, be they people or abstract concepts, is not covered by the rules at all IIRC, leaving it to the aesthetic requirements of a given game.

One exception is that if you choose a given NPC to have a refresh scene with, which obviously isn't feasible with the 'threat-as-pc' model, that NPC usually gets refreshed, too, as the standard refreshment requirements are mutually applicable. If you want more modeling as SGC, see these untested ideas:

Secret of Resilience
You cannot just ignore certain things and hope they go away. For every scene this threat is ignored, it recovers one Pool Point. For every session it is ignored, it gets one free Advance to advance Pool or Abilities. You cannot buy new Abilities nor open up 0 point Pools. Prerequisites: This Secret is only available to abstract threats.

Secret of Underestimation
Some things develop in unexpected ways when left unattended for too long. Abstract threats with this Secret may add new abilities or open up 0 point Pools with Advances gained through the Secret of Resilience. Prerequisite: Secret of Resilience, only available to abstract threats.