does it literally say it "has nothing to do with"?
Ctrl-f tells me that no, it does not.

If a problem were solved, then the problem would be solved. But that doesn't mean that every problem is best described as a "solve the problem"-problem .

Indeed, if the mass that exits the body (including via respiration) is more than the mass that enters it, then the mass of the body decreases. This is obvious. If you think that people advocating different focuses don't believe this, I think you are for the most part mistaken.

When people say that something "is an <X> problem", I think they generally mean (something along the lines of) that the most useful way (or, one way among the more useful ways) to think about the problem, is to think of it in terms of <X> , or that <X> is important to think about when trying to solve or understand the problem.

So, when someone says "It is a hormone problem, not a calorie problem", they aren't saying that human bodies violate conservation of mass, they are saying that the best way to understand the problem is through hormones, and how the hormones influence the mass in vs mass out.

When someone is drunk, they tend to behave differently. Surely you understand this? When someone is hungry, they tend to behave differently.

"In the future, eat less and exercise more." Is not an atomic action that a person can take at a given time. A person in the moment makes a decision as to what to do in that moment, and this can include thoughts or other mental actions with the goal of influencing their future decisions.
But, if one's current "decision" to do something in the future is only a mental action with the goal of influencing the future actions, then to succeed in influencing those future actions, doing things that influence one's body chemistry and thereby influence one's future actions, can be helpful, and possibly more consistently effective than merely making some mental actions.

Suppose one wants to act in a professional and formal manner during a meeting which takes place in a few(?) hours. If one has this goal, then it may be helpful to currently refrain from drinking large quantities of alcohol.
If one has adhd and needs to be able to focus on some task later in the day, that may be a reason for them to not refrain from taking their prescribed medication.

Our decision making processes are not like a RL-agent simply getting data in and sending actions out, but always using the same process, but rather, our interactions with the environment can influence our decision making processes.
We can get drunk. we can consume caffeine. We can consume things that influence thought processes in more radical ways (like, hallucinogens or whatever). A railroad spike through the brain can drastically and in a long-term way alter someone's behavior.

If someone has an alien brain-slug on their head that compels them to punch spotted dogs that they encounter, the solution to this is not to tell them "stop punching spotted dogs", but to tell them to remove the alien brain-slug. This is true even if the former would result in them sometimes successfully resisting the compulsion to punch spotted dogs.

(?) : I don't actually know how long it takes for someone to become drunk or cease being drunk, as I've never really been around people while they have been drunk.