I detect the sarcasm but others may not. As a thought experiment I present that any emotion can always be felt in the body.

If you feel nothing, no emotion or no sensation in the body then that is also a felt emotion in the body as a lack of feeling.

The human system really has only three inputs your conscious brain has control over (and they're almost all 'loose' controls). Loose controls meaning imagine feeding birds, you don't feed the individual birds you just provide seeds and let them figure it out. Your inputs to your body are rarely localized, you just provide signals and your body figures it out.

So, three inputs.

Energy input as food/drink, how fast you breathe in. Energy output as what you do in the world and how much your muscles exert themselves.

The third input to your body is your stress response as interrupted by your brain. Stress in this case can be pain and discomfort, but also any other input or thought from your senses.

Your body doesn't know that a lion jumping out of the grass is terrifying, it just responds to your brain throwing terror seeds at it.

Your body doesn't know that seeing "23 53 34 78 and bonus number 5" means you just won the Powerball lottery, it's just responds to the your brain throwing happiness seeds at it.

Like you said, mental health can be systemic, but having bad inputs can stress you out as well. If your problem is mainly bad inputs, then you can control your response, just in a loose way rather than a tight way that we humans seem to prefer.

I don't agree. Our perception of the world is colored in the gut and served to the conscious mind. When I was living in New York, the jingle of the ice cream truck draw me crazy, it was torture. But for kids, it was happiness because the gut microbes feeding on sugar send a message to the conscsious mind to buy the sugary stuff and they created an irresistible desire for it. This is all done in the guts. Some people can remain cool under any adverse situation because they have a healthy gut.