The fresh plum and its dried counterpart, the prune, are fundamentally the same fruit, yet they possess vastly different effects on bowel regularity. While plums are a healthy source of fiber and nutrients, prunes are widely known as an effective natural laxative. This difference in digestive power is not due to the creation of a new chemical during drying, but rather the result of concentrating the fruit’s existing laxative compounds.
How Drying Concentrates Active Ingredients
The transformation of a plum into a prune involves a controlled dehydration process, typically using hot air. A fresh plum consists largely of water, which dilutes the fruit’s solid components. The industrial drying process removes the majority of this water content.
This removal of moisture results in a significant concentration of all chemical constituents per unit of weight. The sugars, fiber, and laxative agents spread throughout the plum’s high water volume are now packed densely into the smaller, shriveled prune. This physical change is the reason why a small serving of prunes delivers a much higher dose of active ingredients than the same weight of fresh plums.
Sorbitol The Primary Osmotic Laxative
Sorbitol, a sugar alcohol naturally present in plums, is considered the primary chemical driver of the prune’s laxative effect. The drying process concentrates this compound, resulting in prunes containing approximately 14.7 grams of sorbitol per 100 grams of fruit. This is a far more potent dose than the highly diluted amount found in the fresh plum.
Sorbitol’s mechanism is classified as an osmotic effect, meaning it draws water into the digestive tract. Sorbitol is poorly absorbed by the cells lining the small intestine, allowing a large portion of it to pass into the colon undigested. Once in the large intestine, the high concentration of sorbitol creates an osmotic gradient.
This gradient pulls water from the surrounding tissues and bloodstream into the intestinal lumen, increasing the water content of the stool. The added moisture softens the fecal matter and increases its volume, which stimulates the intestinal wall. This combination of softer, bulkier stool triggers the body’s natural reflex to evacuate the bowels.
The Supporting Roles of Fiber and Phenolic Compounds
While sorbitol is the primary osmotic agent, two other classes of compounds concentrated by drying work alongside it to enhance the overall effect. Prunes are a rich source of dietary fiber, delivering about 6.1 grams per 100-gram serving, which includes both soluble and insoluble types. The insoluble fiber adds significant bulk to the stool, helping to speed its passage through the colon.
The soluble fiber dissolves in water to form a gel-like substance that further softens the stool and makes it easier to pass. Together, these two types of fiber physically contribute to the mass and consistency required for efficient bowel movements. Another element is a group of compounds called phenolic acids, such as neochlorogenic and chlorogenic acids.
Prunes contain substantial quantities of these phenolics, providing about 184 milligrams per 100 grams. These compounds are thought to have a mild stimulant effect on the colon, separate from the osmotic action of sorbitol. Specific phenolic derivatives, like dihydroxyphenylisatin, are believed to directly stimulate the muscles of the intestinal wall, increasing peristalsis. This combination of osmotic water retention, physical bulking, and muscular stimulation creates the unique laxative action of the prune.