Twice I have been on very extreme calorie counting regimens for months at a time combined with substantial weight lifting and cardio.
Both times I have observed that if I reduce calories the first thing that happens is I start to feel colder in the same environments. My body adjusts to my new caloric intake by reducing my metabolic rate it seems.
I learned about the idea of a “set point” fifteen years ago and I believe it’s related to what I’ve observed.
I have friends who can do something as simple as cutting out a morning cappuccino and they lose weight as a result. If I do that, there is no measurable difference unless I cut much deeper and substantially increase activity at the same time. Then the weight comes off for a bit and then plateaus again, sometimes for weeks or until I make another adjustment.
One of the times I went through this weight loss regimen I had an air displacement plethysmograph near the end of the weight loss that concluded I had 178lbs lean body mass. I had likely bulked up a little through all the weightlifting I was doing but have always had a fair bit of muscle so you might expect my resting calorie burn to be very stable and for small adjustments in calories to not impact resting metabolic rate, but that’s not what I observed in practice.