The "gut-brain axis" is mostly bullshit invented to cope with the fact that doctors have sent patients to shrinks for decades with real sicknesses. Everybody knows you feel bad when your digestive is out of balance. It's the same english word for "I'm sick" and "I feel sick" since forever. No magical newly found "gut-brain axis" needed.

Eating junk food, especially sweetened food is a drug. You can do a withdrawal and get the reduction of food noise reported with semaglutide without getting dependent on another drug with so far unknown long-term effects.

But the drug feeds the flora in your gut, which tells your brain to crave more of it.

Like if you completely cut off sugary foods for 2-4 weeks you won't crave them as much. Why? The gut flora that feeds off sugar specifically dies off and can't send as strong signals to your brain.

Thus: gut-brain axis. It's a thing and will become more important when we study it more. Your brain isn't as much in control as you think.