I use My Fitness Pal to track my calories. I also frequent the forums there, and I see a lot of people posting about under eating - I mean not eating more because they're not hungry. I think these posts are inspired by a warning the website gives any time you eat less than 1200 calories in a day. I've experienced this myself, quite a bit. I have a calorie limit of 1500 per day. Most days I eat around 1300; some days it's more like 1600. But sometimes I only eat about 1000 calories, and I feel fine when I do this. Sometimes I'll even go a few days in a row only eating 1000-1100 calories. I often go over my calorie limit after doing that, but so long as my 7-day average is below 1500 I really don't worry about it.

The point is, it always bugs me when this question comes up because it seems so counter-intuitive to tell people to ignore their appetites and eat more. So what's the deal? Surely, Grok had times of famine and fasting. I don't doubt there were days (maybe even weeks) when he couldn't even average 1200 calories a day. There's all kinds of advice available about calculating the upper calorie limit. But the lower limit is 1200 for everybody? Where does that come from? What does the science say?