Will eating black goji berries turn your stool black?

Consuming black goji berries may cause dark-colored stools; however, this discoloration can also result from iron supplementation or upper gastrointestinal bleeding.

1. Possible benign cause: Darkening of stool after consuming black goji berries is typically due to excessive intake. The anthocyanins and other pigments in black goji berries interact with gastric acid and intestinal food residues, leading to temporary stool darkening—a generally harmless and self-limiting phenomenon requiring no specific intervention.

2. Iron supplementation: If stool darkening persists after discontinuing black goji berry consumption, it may be attributable to recent use of iron supplements—such as ferrous sulfate or iron dextran. Unabsorbed iron ions react with sulfides in the gut, forming ferrous sulfide, which imparts a black color to stool.

3. Upper gastrointestinal bleeding: Persistent black, tarry stools (melena), especially when accompanied by epigastric discomfort or pain, may indicate upper gastrointestinal bleeding. Blood from lesions in the esophagus, stomach, or duodenum undergoes enzymatic degradation during transit through the intestines, resulting in the characteristic black, foul-smelling stool. Untreated, such bleeding may progress to complications including perforation.