Stress somehow causes reduced immune system (Some born with reduced immune system or low serotonin levels too), then grows the harmful bacteria you eat/drink/breathe. Like Mycobacterium Paratuberculosis which comes free with industrialized city milk.
Then you get IBD or TB or intestinal TB and more stressed, less immune and it goes into a cycle..
How does, city milk get Mycobacterium?
It (Johnes disease=IBD of animals) is common in stressed industrial cows standing still all day long(stressed) and fed with optimal industrial food and antibiotics to grow better.
Just like us:)
That is why; antibiotics, probiotics, fresh air, yoga, ldn, dietzia, SCD, fecal transplant, pigworms, exercise helps some temporarily.
Some of these strenghten immunity, while others kill the bacteria (good and bad=mycobacteria).