> Why only more vegetables? Isn’t fiber also in some other food?

Fiber is in some other foods, but not at the same ratio of fiber to calories; given that calorie surplus is also a common source of health problems in the developed world, vegetables are generally the best fiber source to add.

The amount of fibre in vegetables is enormous compared to most other foods, especially including “high in fibre” manufactured foods.

Fiber being a type of carb is also found in other high carb foods like beans, whole grains, potatoes (with skin), and popcorn. Beans are the best source of fiber by a mile in terms of quantity.

What makes beans better than psyllium husk, which has been shown to substantially lower cholesterol?

I don't think I said anything of the sort. Regardless, fiber is food for the microbes in the gut. Eating fiber from a diversity of sources is important as well as quantity.

What kind of beans, baked beans? Fava?

Black beans, kidney beans, white beans, garbanzo beans, lima beans, black eyed beans.... we can go on if you like. Don't forget the huge variety of lentils as well.

Any really. 1 cup of baked is 14g and fava is 9g.

There are two different kinds of fibers: soluble and insoluble. The insoluble one is the most important for your gut and the one in the article. This fiber you will only find in vegetables and fruits, in particular in sturdy ones such as beans, nuts and full grains.

Isn’t soluble fiber what feeds your gut bacteria?

Your gut bacteria are already getting plenty of food, but to digest the food efficiently, they also need something to hold on to. This is the function of the insoluble fibers.

Do you have a source on this? It doesn't match my understanding.

I get my fiber from oatmeal. Simple plain rolled oats, no sugary additives, roast with a bit of olive oil in a pan to unlock their full nutritional potential, then cover with enough water, add salt and let simmer. Consume with appropriate additions as desired, I usually go for plain yogurt.

You wrote: <<roast with a bit of olive oil in a pan to unlock their full nutritional potential>>

I never heard of this technique before. I tried to Google about it, but I cannot find any scientific studies about it. (I found plenty of pseudo science websites touting it.) Can you point to any scientific studies about this technique?

Personal observation is scientific.