None of that matters, it's like jitter on a clock line. The timespans we are talking (months), these differences vanish. I'm sure there are tons of intricacies

None of that matters, it's like jitter on a clock line. The timespans we are talking (months), these differences vanish. I'm sure there are tons of intricacies in how metabolism works, but glycogen storage in a human is about 2000 kJ. Once your deficit surpasses that (and we'll happily allow a multiple to account for any error here), your body will either consume fat or you'll experience actual low blood sugar and drop dead.