Why do beets turn your poop and pee red?

After you eat beets, you may get a shock when visiting the restroom: Your poop looks slightly pink, or sometimes dark, berry red.

This rather unnerving experience may make you wonder, "why do beets turn your poop red?"

The answer lies in betanin, the reddish-purple pigment that gives red and purple beets their vibrant color, Whitney Linsenmeyer, an assistant professor of nutrition and dietetics at Saint Louis University in Missouri and a spokesperson for the Academy of Nutrition and Dietetics, told Live Science by email. The same pigment is not found in golden beets, which instead contain yellowish pigments called betaxanthins.

Betanin is not only a pigment but also a strong antioxidant, meaning it can neutralize reactive molecules called "free radicals" in the body. By stabilizing free radicals, "it may help prevent damage to DNA and other cells and is also considered to have anti-inflammatory properties," Linsenmeyer said.

Related: Nine benefits of antioxidants: From disease prevention to healthy aging

However, betanin has a low bioavailability, meaning little metabolized betanin enters the bloodstream, so the body can't make full use of the compound. The pigment is highly resistant to digestive processes, and only a fraction of the betanin we consume can get absorbed by the cells in the gut, Linsenmeyer said. Lab-dish and animal studies suggest that roughly half of the ingested betanin gets broken down, mainly in the intestines, according to a 2021 review published in the journal Molecules.

Betanin that is not broken down by the body passes through the digestive tract largely intact. That means it may end up excreted with poop, turning it red or pink as a result. "This is a normal reaction observed in about 1 in 10 people," Linsenmeyer said.

This widely cited statistic likely comes from a 1963 study, which suggested that 10% to 14% of people experience "beeturia," a phenomenon where beets turn your urine red or pink. Beeturia happens when unmetabolized betanin passes through the kidneys and into urine, but it's often accompanied by betanin turning a person's poop reddish, as well. So the two phenomena are closely linked.

"It is considered a benign condition that may persist for a few hours after the meal," Linsenmeyer said of beeturia.

Some studies initially suggested that a person's likelihood of experiencing beeturia might be linked to genetic factors or to iron deficiency, but more recent studies have concluded that the effect is more likely caused by the body's limited ability to metabolize betanin, according to the 2021 review.

"If you notice discolored urine several days later, however, this is not likely caused by eating beets and warrants a call to your doctor," Linsenmeyer said. Urine with a persistent red or pink color can indicate presence of blood, and according to Penn Medicine, bloody urine is a common sign of structural abnormalities or diseases within the urinary tract.

The exact time it takes for beets to turn your poop red can depend on how long it typically takes you to digest food. If you're concerned about your stool turning a reddish color, doctors can test a sample to rule out the presence of blood, and along with that exam, they'll likely ask if you've recently eaten something that might have turned your poop pink, according to the National Library of Medicine's MedlinePlus.

This article is for informational purposes only and is not meant to offer medical advice.