These kind of comments without more context really serve to confuse the situation. If you only ate 1400 calories a day (a brutal challenge for lots of people) and you didn't lose weight it's because your BMR is 1400.

So.. are you 5'2" female or a 6'3" male? 1400 is (potentially) appropriate for one and brutally low for another. Gained fat FAST after eating more? Well sure if you went from 1400 to 2800 and your BMR is 1400 that's gonna make anyone gain weight. Faster than your normally would because your metabolism changed based on your previous input? That doesn't track with conventional knowledge.

I was holding steady with probably a 3k/day diet before that. Abs visible, full-on six-pack if I had a really active week (went swimming a lot in a Summer week, stuff like that). Down from ~4k/day of pure junk food in high school (trim figure and maintained that just fine at that rate, TYVM—I do not know what teenagers do with all those extra calories, it's like magic). Not an athlete, so no Michael Phelps routine doing anything, just young-person metabolism and a lot of weight lifting.

I did the diet to try to make the ol' abs pop even more, the idea was that I'd get down to where I wanted to be fast then ease up a little and hold there (diet's the main thing that matters, everyone says, after all). It backfired badly. Two months of constantly feeling hungry, to no benefit. I'm sure my metabolism was on the way down anyway (early 20s at the time), but that diet killed it dead in just a couple months.

Weight lifting continues to be more effective for me than it "should" be according to common wisdom, even if I'm not doing enough to pack on more muscle. Whatevs.

[EDIT] Incidentally, I wish dieting worked as well for me as all those online calculators say, because I find it a lot easier than working out. Takes negative time, for one thing, and costs negative money. It's great.