I was warned recently that eating beets can cause reddish-purple urine, which got me thinking.

Blood is filtered by the kidneys to produce urine, high school biology. So if a meal of beets can dye urine reddish-purple, due to betalain pigments from the beets making it into the urine, would that mean that the same betalain pigments also dye the blood itself reddish-purple?

I tried to find an answer online, but all the results for any search containing the most relevant words, 'dye', 'beets', 'urine', and 'blood', only seem to turn up results about beets changing the color of urine, not about beets changing the color of blood. Is this indeed the case? Is the effect of a large meal of beets noticeable upon, say, a blood draw?

  • 1
    The color of blood is determined by the red cells and not the plasma. Imagine how much plasma you would have to alter to affect a 10 cc draw. Dec 28 '17 at 16:19
  • I'm not a scientist, but I once tried to find an answer to this very question, by eating A LOT of beetroot the evening before donating plasma. It did not dye the plasma purple. What a disappointment.
    – Steph
    Oct 15 '21 at 4:43

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