There are a lot of studies showing leaky gut induced by an introduction of a pathogenic bacteria to the microbiome. Also IGA, Host defense peptides, and pretty much every other antimicrobial defense protein has been shown to reduce intestinal permeability. I would say that mucosal immunity is the most important factor in leaky gut.
I agree with you on your assessment of this. Increase immune function and then use specific anti-microbials.
Colostrum, thymus extract, nutrient support (vit D from sun, vit A from food, vit K from food, vit C from food etc.), solid diet would all be helpful for increasing immunity.
Regularly drinking green tea (only high quality) is a good way to both stimulate weight loss as well as modulate the microbiome. There is an incredible amount of research showing green tea leads to very significant fat loss as well as lowering lps (endotoxins).
Green tea can often be high in flouride, as it accumulates it. This can negatively impact thyroid function. Fruit juices, whole fruit, coffee, chocolate, herbs, spices, specific safe vegetables, all have these plant compounds. There are studies for many of these foods protecting against lps, and modulating the microbiome. These plant compounds (polyphenols, flavonoids, alkyloids, etc.) are antibiotic to many pathogens, while semi-neutral/ bacteriostatic to the the supposed neutral species. Only certain bacteria seem to be able to use these compounds as a fuel source and they often convert them to other interesting compounds. We absorb a fraction of many of these compounds directly, instead they go to the large intestine and are fermented by specific species.