system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do grains have so many more carbs than other plant foods, like nuts or lettuce?

Googling isn't helping, because the results are all from health and diet pages. I'm trying to find a science answer.

\[Request\] Please try and actually explain this to a 5-10yo. I have a kid in that age range who's the one actually asking the question. I can do my best to bring an "I graduated high school" answer down to his level, but I might struggle to bring an "I've completed some college and have a basic background in biochemistry" answer to his level. Thanks!
gpt
Grains and nuts are both seeds that store energy differently to support a newly sprouted plant.

Grains store energy as starch that gets converted into sugar. Both starch and sugar are carbohydrates. This helps a grain seed grow quickly into a grass plant.

Nuts store energy as fat. Fat can store more energy than carbohydrates for the same weight and helps the seed grow into a mini tree.

Lettuce and other greens are the leaves of a plant. Leaves try to maximize surface area against volume to absorb the sun with the least amount of material. That's why they cook down very easily. They also are high in fiber from the support structures in the leaf.