I thought most overweight Americans (I have sympathy, I'm one too) could fast for 3 weeks or a little more? People who fast usually say they're starting to feel good and energetic about day 3.
It turns out that all that fat really is like a giant extra-length fuel tank.
And many, many Americans have enough fat on them to break 3 months without eating a calorie. It might, in a bizarre way, save some of them.
(Micronutrients might be a problem but is much easier to solve than the calorie problem.)
Also, the initial onset of ketogenesis from fasting is very rough for people who aren't used to it. Most people's bodies are not used to it, and they won't be able to think clearly, they won't have much energy, etc.
I wonder suspect this would be alleviated if survivors managed to get like 300 calories a day of various foods, which seems more likely than pure starvation.