I don’t think it does. Lettuce might provide some nutrients to us, but for fiber, which is what the gut bugs want, cooked or raw root or cruciferous type vegetables are far, far better. I think for the dark leafies including kale and herbs, it’s for the content and nutrients thst we eat them.
Well, I’m thinking there’s a distinction between soluble and insoluble fiber. Insoluble fiber is cellulose and passes through our digestive tract undigested. It adds mass but not energy. Soluble fiber is digested by the gut biome and is used as energy by the friendly bacteria. Those friendly bacteria are sort of the heroes of nutrition and don’t get the credit they deserve, at least for now, it would seem. But nutrition science seems to be pointing in the direction of appreciating those friendly little guys.