Eating beets and seeing your pee turn red could indicate deficiency of iron.
In one study, half of subjects with iron deficiency anemia had beeturia after eating a little more than a quarter cup of beets compared with 14% of healthy controls. The beeturia decreased substantially after correction of iron deficiency .
Tunnsessen and friends, in a similar study, achieved a similar response with iron repletion. They also rated the degree of beeturia in their subjects. Those with low blood iron and hemoglobin had the most severe beeturia .
Why does this happen?
Beets contain compounds called betacyanins, one which is called betanin.
Your body regulates iron status, in part, by changing the expression of iron transporters in your intestinal tract. If you have iron deficiency, your intestinal tract increases it’s ability to pick up more iron.
Apparently, betanin has no problem getting intimate with our proteins that help us absorb iron. The result is a greater influx of betanin than that which would normally occur. This extra betanin makes it’s way to your kidneys where you are given evidence of your earlier beet feast. More betanin, darker urine!
What does this mean for you? If you notice that your urine is much darker than normal after chowing down on some beats, you next want to ask if you are experiencing symptoms of iron deficiency.
Breathing difficulty on exertion?
If so, consider discussion of checking your iron status with your doctor!
 Watson, W. C., R. G. Luke, and J. A. Inall. “Beeturia: Its incidence and a clue to its mechanism.” British medical journal 2.5363 (1963): 971
 Tunnessen, Walter W., Charles Smith, and Frank A. Oski. “Beeturia: a sign of iron deficiency.” American Journal of Diseases of Children 117.4 (1969): 424-426