I lean towards it being the products of fermentation rather than the change in microbiome that's at work here--give mice acetic, butyric, or propionic acid, all three have been shown to have an anti-inflammatory effect, beneficial effects on glucose metabolism, etc. Gut bacteria are important, partly because they produce these short chain fatty acids, but a little harder to steer, subtle changes don't impress me much. Fermented foods are fine, but a bit of vinegar on your veggies might have a similar effect.