I think the point being made was that the enzyme used to break down cellulose is only made by bacteria, whereas the enzymes used to break down carbs, fats, and proteins are produced by the pancreas. Digestion is complicated though, teeth and stomach acid are also digesting in a way so it’s all an oversimplification
Your gut biome is the only way you can digest leafy things. Without them most of it would just stay in there, or go right through you.
Your gut biome is how you digest everything
I think the point being made was that the enzyme used to break down cellulose is only made by bacteria, whereas the enzymes used to break down carbs, fats, and proteins are produced by the pancreas. Digestion is complicated though, teeth and stomach acid are also digesting in a way so it’s all an oversimplification