Some people just need less food to survive.
I’m actually most comfortable and happy on a fast: day 2-3 I feel best, day 4-5 I start to struggle a bit, probably partly because I always keep exercising on a fast (although I don’t hit it as hard as I do when I eat).
Yet others struggle hard to make it to noon before eating,
I have always fasted through my life, even as a teen I’d just randomly go all day without eating, sometimes into the next day, without even thinking about it. I think some people honestly just need less, if you consider the huge scope of dna in the human population doesn’t it make sense that a general calorie amount for everyone can’t really be calculated.