It´s interesting to know where that rule comes from. It helps judging it.
To my observation the poor may be affected less by a temporary interuption of food supplies. I know a few people who actually have only food for a day or two in their house (not counting the spare supplies on their bodies). None of them can be considered poor by any standards. They can afford to buy when the items are not on sale or go and eat in a restaurant (which may run out of food fairly quickly too).