Your stomach lining is only days old

The inner surface of your stomach is only days old. That does not mean the whole organ is replaced so quickly. It applies to the layer of mucus-making cells on the inside, the surface cells that face the contents of the stomach.

Those cells work in a harsh place. They are continuously exposed to hydrochloric acid and pepsin, a protein-digesting enzyme. Together these are capable of digesting tissue, so the lining has to cope with a mixture that could, in principle, break it down.

Its defences are a mucus and bicarbonate barrier, and a steady supply of fresh cells. Stem and progenitor cells in the stomach's tiny glands keep producing new cells. The surface cells among them migrate upward to the stomach's inner surface and are then shed into the stomach.

How long does a surface cell last? Classic estimates say the layer is replaced every few days, and one long-standing figure is about three days. A 2021 study of human cell turnover by Sender and Milo, published in Nature Medicine, put the average lifespan of these cells at 13 plus or minus 9 days. That is nearer two weeks, and the authors acknowledged wide uncertainty.

The fast renewal belongs to the surface layer only. Other cell types in the stomach lining, deeper in the gastric glands, turn over far more slowly. Most of them take about 40 to 70 days, and chief cells last at least six months. Those figures were measured mainly in mice.

For comparison, a red blood cell lives about 120 days, or about four months. The cells at the stomach surface are a fraction of that.

Because the surface cells last from a few days to about two weeks, the cells that lined your stomach a month ago have since been shed and replaced. The lining that met your meals last month is already gone.