I am reading a lot about gut health lately too (I’ll have to watch that documentary). There are different types of gut issues (SIBO, IBS, Gluten intolerance, Candida overgrowth, etc.) and beneficial foods may differ depending on whether one has one of those issues.
For instance, leafy green vegetables are generally healthy, but they remain in the digestive tract longer and take longer to digest. Some people might also have a sensitivity to nightshade vegetables or lectins and some experts warn against using seed oils, which cause inflammation.
Everything I read says supplements don’t do anything but temporarily mask symptoms that won’t ultimately go away unless changes are made in what one eats.
Getting tested for food sensitivities is helpful in determining which foods to avoid. Also doing a food elimination/low FODMAP diet can help.