Dear Dr. Blonz: What is known about how our digestive system can renew itself? Can materials normally eliminated end up stuck for several months and cause various problems? There are “cleanse” services that provide colonics to unclog and resolve these issues, and I would like information about whether there are benefits to undergoing this procedure.

— F.S., San Jose

Dear F.S.: There is misinformation on this topic, often from those selling products or services that they claim address specific problems. The cells lining our digestive tract don’t last long. This is crucial, because they are constantly exposed to mechanical stress, digestive enzymes, microbial interactions or unwanted substances that have been consumed or formed from breakdown products, or medications detoxified by the liver and deposited into the digestive system for elimination. The ongoing renewal helps maintain gut integrity, optimize nutrient absorption and support our healthy microbiome.

Different sections of the digestive system have varying rates of cell renewal. The cells lining the stomach turn over every two to three days due to the wear and tear of its harsh, acidic environment. In the small intestine, we have cells (enterocytes) responsible for breaking down food and absorbing nutrients; these cells are replaced every two to five days. In the large intestine, where the microbiome calls home, turnover is slower and can take four to five weeks. This delay makes sense as we want more stability for our microbiome.

Claims that undigested waste and toxins can get stuck for months and need to be routinely flushed using colonics are based on pseudoscience, not objective evidence.

Now, there are specific medical conditions that can affect the ability of food to move through the digestive system, referred to as digestive motility. These are uncommon clinical conditions that require clinical diagnoses. (For a discussion of various health conditions affecting motility disorders, see b.link/ngpgfet.)

As a general rule, after food has been consumed, it will, under normal circumstances, exit the body within three days. Claims of months- or years-old waste typically come from detox product marketing or downright pseudoscience to encourage your interest in their colon cleanses or supplements. Conditions like severe constipation, intestinal obstruction or medications or conditions impairing motility could result in delayed elimination — but not monthslong accumulation in an otherwise healthy system.

Kensington resident Ed Blonz has a PhD in nutrition from UC Davis. Email him at cctimes@blonz.com