I mean, yeah, of course if you eat less than your body needs, you will lose weight, nobody is denying that. You can lose weight drinking only coca cola every day. Now, how _easy_ that would be, how much hunger one would feel, the effect on health, mental health, energy, what the rebound is after the diet is done etc., that's a completely different discussion. And another discussion is how much the weight loss is sustainable/maintainable in the long term.

So yeah, in a vacuum, with a perfectly spherical cow, it's not that far off.