In livestock we feed protein for body weight and add on more for growth.

We can access proteins and carbohydrates in plant material. How much depends on a couple factors: the age of the plant in its development and the processing.

We can not use tiny seeds very well via chewing so we grind these: chia, flax, corn, etc.

Many plants we eat young, when the lignans are not very developed. Think spinach, kale, and other leafy types.

We dont eat corn stalks, but cattle and horses can. Better results if it is ensiled first. But even the feed value of corn stalks, and hay is determined by the age and amount of lignans. First cut hay is very stemmy compared to second cut. My sheep love the second cut and hate the first cut. My horses love the second cut and pick away at the first cut. Humans cant eat either.

We eat the tender plants or young plants, before they are woody. OTherwise they need to be processed in some way. Perhaps crushed and steeped. Perhaps ground ( think bark of the cinnamon). Whatever size the particles are, the processing makes more nutrients available but we still cannot digest lignans, aka fiber.

( ruminants have a vast microbiome load that works on cellulose, very little uses lignans.)