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Articles June 2011 Issue

No Joke: Prunes Work Better vs. Constipation

Long the object of jokes, prunes may now have the last laugh. New research demonstrates that prunes (dried plums) are more effective than psyllium fiber in combating constipation.

In a randomized control crossover trial funded by the California Dried Plum Board but conducted independently at the University of Iowa, Satish Rao, MD, PhD, and colleagues recruited 40 constipated men and women, average age 38. Participants received a total of 6 grams of daily fiber from either 50 grams of dried plums (1.76 ounces, or about 5 to 6 prunes) eaten twice a day or 11 grams of psyllium (1 tablespoon, such as Metamucil) taken in water twice a day. Each regimen was followed for three weeks, with a one-week “washout” period in-between. Participants kept diaries of symptoms and their success in relieving constipation.

Although both supplements increased the number of complete bowel movements, the use of dried plums produced a greater increase than psyllium. Measures of stool consistency also improved more when subjects were consuming prunes.

Robert M. Russell, MD, professor emeritus at Tufts’ Friedman School, comments, “Prunes have been an old-fashioned remedy for a long time so I’m not surprised at these results.” Indeed, prunes’ reputation could have been a factor in the results, he cautions, since obviously the study could not be “double-blinded”—that is, participants had to know when they were getting prunes rather than psyllium. “Participants might have heard that prunes are good from their grandmothers and could have been influenced to think that they would be really a good remedy.”

In any case, the need for an effective constipation treatment that’s well-tolerated is no joking matter, according to Dr. Rao: “There is an unmet need for natural, safe alternatives. Dried plums (prunes) have been traditionally used for constipation, but they have not been scientifically studied for this effect.”

As recently as last October the European Food Safety Authority’s (EFSA) Panel on Dietetic Products, Nutrition and Allergies rejected a proposed health claim for prunes and bowel function, citing insufficient scientific evidence.

Study participants rated psyllium and prunes equally palatable, and both were safe and well tolerated. Psyllium, derived from plant husks, is commonly recommended by physicians for constipation relief and sold under a variety of brands. It’s a soluble fiber—meaning it dissolves in water—and must be taken with fluids. Psyllium is especially high in a type of fiber called mucilage, which absorbs and holds water, causing it to swell and supplying the necessary bulk for regularity.

Prunes, on the other hand, contain both soluble and insoluble fiber in roughly equal amounts. Insoluble fiber, which doesn’t dissolve in water but does also bind with water in the intestine, promotes movement of food through your digestive system and increases bulk.

Prunes also contain about 15 grams of sorbitol (a sugar alcohol found in fruits that’s sometimes used as a sugar substitute) per 100 grams; Dr. Rao notes that sorbitol has been shown to have a laxative effect. Every 100 grams of prunes also contain 184 milligrams of antioxidant polyphenols.

“Since we tested an equivalent dose of dietary fiber,” the researchers concluded, “it is likely that the clinical improvement observed with dried plums is most likely due to the other beneficial components of plums over and above its fiber content and /or the blend of soluble and insoluble fiber.”

TO LEARN MORE: Alimentary Pharmacology & Therapeutics, April 2011; abstract at dx.doi.org/10.1111/j.1365-2036.2011.04594.x. “The Facts on Fiber,” February 2009 Healthletter Special Report.

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