But why not call the body's bluff? Cut input further! And then cut it again. Be more stubborn than your body.
Not saying it would be easy. It would probably be really hard. Not sure if I could actually do it if I had to. But surely, it is possible?! What little physics I know seems to strongly support it.
People with health conditions that directly depend on them losing weight will need specific ways, adapted to them, to lose that weight. Telling them “just eat less dumbass” (which is an actual advice thrown at people, almost verbatim) is condescending, ignoring the complexity of dieting, and only looking at it short term when they are trying to change the rest of their life.
We wouldn’t throw “money in/money out” mantras at random bankrupt people (or do we? I can’t tell anymore), we shouldn’t do that to overweight people either.
The entire personal finance sphere is based around this advice. Make a budget, cut costs, get spending under income enough to pay off debt. So yes, we do distill it down to “money in/money out” for people who mismanage their money. Fortunately, when it comes to money it generally is that simple, provided the income is sufficient to maintain the basic necessities of life.
For people straight in the red, more often than not the advices I've seen applied IRL are akin to talking to one's bank to reevaluate the situation, checking with local institutions how they can help, reviewing tax declarations, giving up on too low paying jobs to completely change their status etc.
To me these changes are often more structural or complicated than just deciding where the money goes or to how much extent.