It’s true that more exercise OR less food will affect size.
Doing those things tend to be issues of habits, willpower, thought patterns (aka situations one has gotten oneself into).
I found that when I sorted out my thoughts and became more self-aware, I was more accurately aware of what I wanted to eat and how much, and lost lots of weight without exercising or dieting at all. I probably was eating less and better, and may have been a bit more active, but I wasn’t intentionally doing those things.
And more importantly, I got my life back, too.