system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we need to consume fat if excess carbohydrates are ultimately stored as fat?

My understanding is that any carbs that aren't used for energy are converted and stored as fat. Hypothetically, could a human just survive off of protein and a lot of carbs?
gpt
Fat has two basic uses for the body: energy storage and ingredient for  stuff, like hormones. The second use can't be fulfilled by stored fat, it must be dietary (eaten) fat.

And no, you can't live without fat, there's even a thing caused "rabbit starvation", which is literally people starving to death because they only ate rabbit meat, which is VERY lean, for a long period of time.