> 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.

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.

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.