system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that the stool is always the same brown color (almost) regardless of what we have eaten, and same thing with urine. But if we eat beetroot both feces and urine becomes red?

All day one eats food of different colour but the "outcome" is always the same, except in this case. Why is that?
gpt
The red coloring in beets (betanin) isn't digestible.  Mostly, though, the color of waste products is mostly not based on what you eat - it's a product of the breakdown of red blood cells.  Specifically, urine is colored yellow by urobilin and feces are colored brown by stercobilin, urobilin, and bile (a liquid produced by the liver which helps digest fats).  Stercobilin and urobilin are byproducts of the breakdown of hemoglobin.  Since your red blood cells are recycled at a set rate, there's relatively little variation in the color of excretion.