When you don't have enough food on Christmas, what happens when you choose thumbs up?
Step back from the rules and think about it for a second. You don't get to feel good about giving out food if you don't give out the food!

"Do as much as you can" applies to effects (benefits), not costs (requirements). "Spend 5 food" is really a cost here. I would not permit that option to be picked since the result would make no sense.