Prunes are widely recognized for their ability to promote bowel regularity, and they can cause diarrhea, especially when consumed in high amounts. This effect results from their unique nutritional composition, which includes compounds that draw water into the intestines and add bulk to waste material. Understanding these compounds and the physiological process they trigger helps to explain why this common side effect occurs.
Key Compounds Responsible for Laxation
The primary components responsible for the laxative effect of prunes are dietary fiber and sorbitol. Dried prunes are a concentrated source of fiber, containing both soluble and insoluble types that regulate bowel function. A 100-gram serving of dried prunes contains approximately 6.1 grams of dietary fiber.
The other significant compound is sorbitol, a sugar alcohol that is poorly absorbed by the small intestine. Dried prunes contain a high concentration of sorbitol, about 14.7 grams per 100 grams of the fruit. This concentration is significantly higher than in fresh plums because the drying process removes water, intensifying the presence of this sugar alcohol. Sorbitol’s classification as a poorly absorbed carbohydrate means that much of it bypasses digestion and moves on to the lower gut, where it exerts its powerful effect.
The Digestive Mechanism
The laxative action of prunes is a result of two separate, yet complementary, digestive mechanisms driven by these compounds. The unabsorbed sorbitol reaching the large intestine creates an osmotic effect. This means the sorbitol draws water from the surrounding body tissues into the bowel lumen to equalize the concentration gradient. The resulting increase in water content softens the stool and increases its overall volume.
In parallel, the fiber content of the prunes contributes to the bulk-forming mechanism. Insoluble fiber adds structural mass to the stool, which helps to speed up the transit time of waste through the digestive tract by stimulating intestinal activity. Soluble fiber absorbs water, forming a gel-like substance that further softens the stool and contributes to its bulk. The combined action of sorbitol’s osmotic pull and the fiber’s bulking effect accelerates the passage of waste, which, particularly at high doses, can result in loose stool or diarrhea.
Safe Consumption Guidelines and Related Side Effects
To benefit from prunes without experiencing excessive laxative effects, consumption should begin slowly and be kept within recommended serving sizes. A typical serving is considered to be about four to six prunes per day, which provides a gentle way to introduce the compounds into the diet. Eating too many prunes, such as 100 grams (about nine to ten prunes), may exceed the body’s tolerance for sorbitol and fiber, increasing the risk of diarrhea. Consuming 20 grams or more of sorbitol can lead to more severe cramping and diarrhea in some individuals.
Adequate hydration is an important part of consuming prunes, as both fiber and sorbitol require water to function properly and prevent constipation. Increasing fiber intake without enough liquid can actually lead to uncomfortable symptoms. Aside from diarrhea, other common gastrointestinal side effects include gas, bloating, and abdominal cramping. These minor symptoms occur when unabsorbed sugars, including sorbitol, are fermented by bacteria in the large intestine, a natural process that produces gas. Introducing prunes gradually allows the digestive system time to adjust, which can help to minimize these temporary side effects.