Rule of threes: three minutes without air, three days without water, three weeks without food. I feel like this rule is dated from a thinner time, so feel free to adjust for BMI.

There are lots of cases of obese individuals fasting for months with no ill health effects. Some even have gone over a year without food.

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.)

I personally have fasted for 28 days. The dangerous part isn't micronutrients, it's electrolytes. Fasting for an extended period can put you at a dangerously low level of certain electrolytes like phosphorus, which upon refeeding, are taken into the cells, which results in levels low enough to cause death. This is why extended fasting regimens should only be done with medical supervision.

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 believe the definition of micronutrient covers electrolytes (including phosphorus), but I see what you're saying. There would definitely be challenges!

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.

There is no way you have that from historical research. Afaik, that level of notes keeping and detail was not available at the time.

In general, in situation like these, the first to die are sick, old/kids and those suffering from malnutrition. It would be super safe to guess that Leningrad at the time and a lot of those (given general state of that country).

It's not from a research, but from the memoirs of those who survived. So it might be not accurate, indeed.

Maybe they're more likely to be eaten?