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The Role of Dried Plums in Digestive Health
Phyllis Bowen, PhD
University of Illinois at Chicago
History of Dried Plums
The dried plums we use today are produced from Prunus domestica, which came from the D'Agen region in France. This is a particularly sweet variety of plum that became popular in Europe in past centuries because it could be dried and kept through the long, cold winters. In fact, that region of France became wealthy because of its exports of dried plums to other northern European countries. The reference to dried plums in the famous poem, The Night Before Christmas - "while visions of sugar plums danced in their heads" - tells us that these fruits were considered a great treat and a delicacy. It is probably true that Europeans historically ate a great deal more dried plums on a daily basis than we do today.
Dried plums are one of first true functional foods. There are records that the Greeks and Egyptians considered them good for digestion and for mouth ulcers, and dried plums have been considered by cultures through the centuries as good for digestion and laxation.
Dried Plums Today
California presently process close to 70% of the world's dried plum supply, about 178 million kg per year. Other areas where dried plums are produced include Australia, Italy, France, Chile and Argentina. The California Dried Plum Board (CDPB) is a commodity board representing the state's growers, who participate in a check-off system for funds to support agricultural and marketing issues as well as scientific research. Around 1997 the Board decided to start looking at the nutritional aspects of dried plums as a marketing platform. A Nutrition Advisory Panel was assembled at that time to guide and systematically direct research, so as to ensure that the research was sound and that marketing was evidence-based. I was and still am a member of that Panel.
Our first action was to collect and review the scientific literature on both the nutritional composition and the health benefits of dried plums. Maria Stacewicz-Sapuntzakis, a plant physiologist at my laboratory at the University of Illinois, was key to this effort, in part thanks to her broad knowledge of languages. The result of that effort was a review paper called "Chemical Composition and Potential Health effects of Prunes: A Functional Food?", which drew from papers in many languages from all over the world. Since that initial effort, the CDPB's Nutrition Advisory Panel has funded 26 studies on dried plums, from which at least 18 publications have been produced.
Composition of Dried Plums
Like many other fruits and vegetables, dried plums are a very complex food. They contain 42 major nutrients and phytochemicals, 55 volatiles and 18 waxes. It is difficult to standardize their composition because it can vary with the growing season, the plant variety, even from plot to plot. As sugarplums, dried plums are sweet, composed of about 37% sugar of which 23% is glucose, but only a very small amount (about 0.6 g) is sucrose. By comparison, raisins are 67% and apricots 37% sucrose. Dried plums are distinct in that 15% of their sugar content is in the form of sorbitol. Raisins have only a trace of sorbitol, and apricots have about 5%. This differing sugar composition of different dried fruits may have implications for their health effects. Dried plums are also higher in dietary fiber at about 6%, fairly high in potassium, and very high in chlorogenic acid and neochlorogenic acid, both quite potent antioxidants. These antioxidants may account for the high ORAC rating of dried plums.
Potential Health Effects of Dried Plums
Dental health. There is evidence to suggest that sorbitol (comparable to the xylatol used in sugarless gums) may be less carcinogenic than other forms of sugar. Christine Wu at the University of Illinois is currently studying the carcinogenicity of dried plums as compared to other dried fruits.
Glycemic index. Because of the high sorbitol/low sucrose content of dried plums, the Nutrition Advisory Panel sponsored research to determine the glycemic index (GI) and found it to be in the moderate range, around 54, versus 100 for glucose. Two recent studies were conducted in athletes to determine whether a dried plum bar or dried plums themselves might be a good fuel for athletic activity, since dried plums appear to elevate blood sugar levels slowly and provide prolonged energy. In these studies, both forms of dried plums compared very favorably to Power Bars and other sports bars, with no side effects.
Laxation. Despite the folklore about the laxative effects of dried plums, there are no clinical trials on this health benefit. We will be sponsoring more studies on this issue to answer questions about the quantity of dried plums that produces laxative effects, and how this may vary for different people at different ages. Interestingly, in some Asian markets dried plums are consumed for the complexion. They believe that if you eliminate toxins from the body, your skin will be better. Once it was thought that dietary fiber was responsible for the laxative, but then it was discovered that prune juice produces the same effect, although it contains no fiber. The explanation for this is most likely sorbitol, which has been found to cause stool softening at intakes of 16-25 g. One cup of prune juice has about 25 g of sorbitol. It is also possible that neochlorogenic acid or chlorogenic acid may play a role, since it was found in another study that chlorogenic acid favored the dissipation of the sodium electrochemical gradient, possibly causing more glucose to pass from the jejunum to the bowel, enhancing microbial fermentation.
Microbial balance. Sorbitol is poorly absorbed, so more is likely to move into colon to become food for bacteria, which in turn produces more short chain fatty acids. In researching the folklore of dried plums, we found that prunes were used as a remedy against diarrhea, cough and mouth ulcers in traditional folk medicine and old medical texts. Infectious agents, bacteria and viruses could cause all of those symptoms. We also found a number of articles suggesting that prune juice and dried plums do have a mild antibacterial action, as compared with many other fruits and vegetables.
Because of the sorbitol content, dried plums act as humectants, and this makes them useful for binding in meat mixtures and particularly in meat substitute mixtures. It has been found that a 2.5% - 10% concentration of dried plum puree mixed into ground meats can significantly reduce bacterial growth. Whether this protective effect also exists in the body is not yet known.
Colon cancer. The CDPB Nutrition Advisory Panel funded study with Dr. Walter Willett of Harvard School of Public Health to determine any association between dried plum consumption and colon cancer in the Health Professionals Follow-up Study and the Nurses Health Study. Such an association was not found, but since 85% of the women and 76% men consumed prunes les than once a month, the study population consuming prunes and the levels of consumption were probably inadequate to provide truly informative data.
Probiotic effects. The Nutrition Advisory Panel commissioned Dr. George Fahey to study the probiotic capacity of 18 different dried plum preparations. Unfortunately, no probiotic activity was found.
In summary, a great deal of research on the health effects of dried plum consumption is ongoing, and a great deal is needed as well. Dried plums appear to be important for good health and can help Americans achieve the Dietary Guidelines for fruit intake and for meeting fiber goals. As well, their antioxidant and antimicrobial effects are beneficial to health and may be further elucidated by future studies.
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