Supposing I take in 100- calories a day, this should be fine, right?

100 or 100 less. 100 less than you are eating now is probably just fine. Eating a total of 100 calories/day is starvation in a big way, not at all healthy.
For what purpose? His would be considered a starvation level intake for anyone if it were the only intake. It would neither be prudent or healthy.