Hello - thanks for asking your question.
If you had a colonoscopy last year and there was nothing other than the polyp, it is reassuring that there is nothing more serious. Being 29 years old, it is less likely that colon cancer is the cause.
Beets can certainly cause the blood-like appearance of the stool. Other possibilities would be a hemorrhoid or reappearance of the anal fissure, both of which could develop in the year since the colonoscopy.
I would continue to observe your stools for the next few days. If there continues to be blood, I would consider seeing a physician for an anoscopy to evaluate for any anal sources of bleeding (i.e. hemorrhoid or anal fissure). If that is negative and the bleeding continues, a flexible sigmoidoscopy may then be considered.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.