Dried plums have a high antioxidant capacity due to high phenolic content.
A serving of dried plum (~5 plums/50 g) offers a complex of nutrients and other compounds, many of which provide more than 10% of the DRI. Especially notable are dietary fiber, vitamin K, copper, and boron. Its complex sugar content with high amounts of sorbitol is probably the reason that its glycemic index (29 for a 60-g serving) is so low for such a sweet food.7 Dried plums have a high antioxidant capacity compared to other fruits, dried or not, depending upon the assay used. The low values of carotenoids, ascorbic acid, and vitamin E point to their high content of phenolic compounds as the contributing factor. Yet their phenolic content cannot explain all of their antioxidant capacity.
TWO AREAS OF INVESTIGATION THAT HAVE BEEN A FOCUS OF CDPB FUNDING
The NAP recommended to the CDPB that they focus on particular areas of research and seek to develop the science in those areas. In retrospect, 2 areas have received the most intense funding. Gastrointestinal (GI) health, for obvious reasons, and bone health, which became an important area serendipitously. These studies are reviewed here with the objective that the reader sees the progression and type of studies funded, how other investigators not funded by CDPB become interested, and how paying close attention to the type of study needed as evidence leads to an official health claim.
Dried plums/prunes have been the subject of many a joke, especially in the United States. Seeking to reposition the fruit away from the jokes and to younger consumers, the CDPB applied to the FDA for a formal name change to dried plum in 2001, which was approved. Surprisingly little research has been published on the effect of dried plum or prune juice on GI function. There are 3 components of dried plum that could affect GI motility: sorbitol, dietary fiber, and phenolic compounds. The sorbitol content of dried plum (10–12 g/100 g or 2 servings) is uniquely high and is equivalent to consuming 12 sticks of sugarless gum or individual candies that can act as an osmotic laxative in high quantities.8 Whether one is affected by consuming high levels of sorbitol is highly variable and seems to be related to the ability to absorb it. Breath hydrogen studies indicated that 71% of healthy adults showed malabsorption after consuming 10 g of sorbitol and 20% reported symptoms of bloating, flatulence, and abdominal pain.9 However, a dose of pure sorbitol would enter the lower GI tract at a faster rate than found in an equivalent dose of whole dried plums.‡ Those with irritable bowel syndrome have a greater likelihood of having a lower absorption potential.8 Phenolic compounds are also thought to have an effect on GI motility.6
High sorbitol content is likely reason for dried plum stool softening effect.
The CDPB funded a number of human studies that evaluated bowel habit with dried plum supplementation at various doses. With these data in hand, the CDPB applied for a health claim to the European Safety Authority.10 After weighing the evidence on these studies and plausible mechanisms, the European Food Safety Authority stated “on the basis of the data presented, the Panel concludes that a cause and effect relationship has been established between consumption of dried plums of ‘prune’ cultivars (Prunus domestica L.) and maintenance of normal bowel function. In order to obtain the claimed effect, about 100 g (or about 2 US servings) of dried plums (prunes) should be consumed daily. The target population is the general population.”10
Details of Studies
Most of the following studies were funded by CDPB but not all of them. Subjects (41 men with mild hypercholesterolemia or 40 chronically constipated men and women) consumed 12 dried plums a day for 8 and 3 weeks, respectively, in the 2 crossover studies. Psyllium was used as the control in the second study. There was a notable lack of adverse GI effects and no increase in the number of bowel movements or decreased transit time. However, stools were softer and there was an increase in fecal weight.11,12 The study by Attaluri et al was the most impressive (not funded by CDPB). Forty constipated subjects consumed either 100 g (10–12) dried plums or 22 g of psyllium for 3 weeks in a crossover design with a 1-week washout. The number of complete spontaneous bowel movements per week and stool consistency scores improved significantly compared with psyllium.12 A 3-month study of 58 postmenopausal women (38 completers) randomized to consume 100 g (10–12) of dried plum or 75 g of dried apple (1.2 g sorbitol/100 g fresh apple) not on hormone therapy (bone health the major outcome) was also submitted to the European Food Safety Authority. Both groups experienced the same mean number of spontaneous bowel movements with the sensation of complete evacuation.13 Another study of 29 women consumed 84 g of dried plum or low-fat cookies for 2 weeks each in a crossover design. Notable was that during the dried plum intervention, subjects reported significantly softer stools.14 A more extensive study of bowel health was subsequently funded by the CDPB in the United Kingdom. A total of 120 healthy subjects were randomized to control or 80 or 120 g of dried plum per day; 14 GI symptoms were tracked over the 4-week period. Of the 104 subjects completing the study, for both doses, dried plum significantly increased stool weight and bowel movements but did not affect transit time. There was no reported diarrhea, but incidence of flatulence and/or reflux was higher in the dried plum groups compared with controls, but symptoms were rare and rated mild.15
We are beginning to explore the question, could dried plum consumption lower the risk of colon cancer by promoting a microbial population favorable to its prevention? We also would like to determine whether 1 serving (5 prunes) would also contribute to bowel health.
Exploring the role of dried plum on bone health seems to be an improbable leap. However, the scientific process is often serendipitous and personal. As I took on the role as NAP member for the CDPB, I noticed that dried plum had an unusually high boron content. I remembered that boron had been associated with strengthening bones in some early animal studies. A young faculty member, Bahram Arjmandi, in my department at the University of Illinois at Chicago had a model for overiectomized animals to simulate osteoporosis, so I suggested that he put in a proposal to study dried plums with his animal model. The NAP advised the CDPB that the proposal was low cost and scientifically worthwhile and CDPB funded the animal project although there was no previous evidence of a dried plum bone connection. To Arjmandi's surprise and ours, the dried plum–treated ovariectomized rats (a good model for postmenopausal osteoporosis) experienced less bone loss than their counterparts.16 Since that first experiment, a number of animal studies using various models of bone loss have been performed funded by the CDPB (as reviewed17). Previous bone loss was somewhat restored in the femur and tibia at a low dose of 5% dried plum powder (w/w), but it took a 25% dose to improve lumbar vertebra. Immobilization leads to bone loss and a dried plum diet performed as well as parathyroid hormone injections to restore bone during the reambulation period in bone mineral density (BMD), bone strength and bone structure.
A study in a rat male model of osteoporosis found that feeding 15% and 25% of the diet as dried plum powder (w/w) for 90 days postcastration prevented loss of BMD, whereas the 5% diet was effective only for the lumbar vertebra and femur. Again, male rats allowed to lose bone after castration showed reversal of that loss with either 25% dried plum or parathyroid hormone. Most interesting was a long-term study where adult (6 months) and old (18 months) mice were fed calorically adjusted diets of 15% and 25% dried plum (w/w) for 6 months. On the 25% diet, bone volume increased 50% in the adults and 40% in the old mice but the control groups lost 24% and 28% of their bone mass, respectively. The most recent study used lower doses (5%, 15%, and 25% w/w) of dried plum in growing mice and found increased cancellous bone of 12%, 36%, and 64%, respectively.18 These investigators observed the dried plum appears to disrupt the balance between resorption and formation with a net effect of more bone and this might be due to a suppression of proinflammatory cytokines.
Some of these studies have been funded by the CDPB and others have not. Almost all of them have used dried plum powder fed at 25% of the diet (w/w), a much higher dose than would be reasonable for human beings. Since these initial studies, efforts to find mechanism and the components of dried plum that are bioactive have led to understanding that dried plum phenolics are not the sole component19 and that dried plum has unique properties compared with other dried fruits.20
Three human trials have been performed. Three months of 100 g of dried plums a day (10–12 dried plums) improved the biomarkers of bone formation in postmenopausal women.21 A 12-month study showed that the same dose could prevent the normal loss of BMD in postmenopausal women. Dried apple had little effect. Both groups were supplemented with calcium and vitamin D.22 The third study assigned 48 osteopenic women to 6 months of either 50, 100, or 0 g of dried plums per day. All were supplemented with calcium and vitamin D. Both doses of dried plum preserved BMD compared with the normal loss experienced by the control group. Bone resorption appeared to be inhibited.23 The GI complaints of subjects were minimal in these studies. One study was funded by USDA, and the other 2, by CDPB. Because we want to be sure of the dried plum effect in humans, we have decided to fund a larger clinical trial by a different set of investigators, using a standard serving size (4–5 dried plums) and higher dose (10–12 dried plums) to characterize the effects on bone mass in this older population of women.
Human studies also show dried plum reduces bone loss.
The most interesting effect of a dried plum diet was recently published. Bone loss caused by ionizing radiation is a health concern for radiotherapy patients, radiation workers, and astronauts. Animals exposed to such radiation experience skeletal damage and an imbalance between bone building and bone loss. They rapidly lose bone mass. Mice were divided into groups and given a selection of antioxidant and anti-inflammatory candidates (antioxidant cocktail, dihydropipoic acid, ibuprofen, or dried plum 25% diet w/w). Various groups were exposed to gamma rays or simulated space radiation. Dried plum was the most effective in reducing expression of genes related to bone resorption and the prevention of cancellous bone loss. The authors concluded that “dietary supplementation with dried plum may prevent the skeletal effects of radiation exposures either in space or on Earth.”24
The effect of whole dried plum on various dynamics of bone growth and resorption is certainly intriguing and worthy of further research and holds great promise as a dietary component that may promote bone health, not only in the elderly but throughout the life cycle.
The experience of scientists with the CDPB may be informative in how such commodity boards listen to scientific panels and determine how to fund and promote scientific studies. Although there are grounds for concern when commodity boards and self-interested groups fund and then promote research that benefits the marketing of their products, great gains can be made with industry/academic partnerships that aid health and well-being. (1) Young faculty may find financial support for their first projects which then form the preliminary studies that aid in successful applications for National Institutes of Health or USDA grants. (2) Studies using whole foods are more difficult to control because of their variable and complex composition. Commodity board funding is essential to clarify the epidemiological findings that point to single foods or food groups as beneficial. (3) All academic institutions decline to enter into financial obligations with industry sponsors that do not allow their faculty to publish results from industry-sponsored research. Investigators are free to publish negative results. (4) The existence of independent scientific panels who direct the research programs of commodity boards is essential to guide commodity boards in the efficient and ethical use of funds set aside for research.
1. Siddiqi N. Publication bias in epidemiological studies. Cent Eur J Public Health
2. Nestle M. Corporate funding of food and nutrition research: science or marketing? JAMA Intern Med
3. Mugambi MN, Musekiwa A, Lombard M, Young T, Blaauw R. Association between funding source, methodological quality and research outcomes in randomized controlled trials of synbiotics, probiotics and prebiotics added to infant formula: a systematic review. BMC Med Res Methodol
4. Khan NA, Lombeida JI, Singh M, Spencer HJ, Torralba KD. Association of industry funding with the outcome and quality of randomized controlled trials of drug therapy for rheumatoid arthritis. Arthritis Rheum
5. Alexander N, Rowe S, Brackett RE, et al. Achieving a transparent, actionable framework for public-private partnerships for food and nutrition research. Am J Clin Nutr
6. Stacewicz-Sapuntzakis M, Bowen PE, Hussain EA, Damayanti-Wood BI, Farnsworth NR. Chemical composition and potential health effects of prunes: a functional food? Crit Rev Food Sci Nutr
7. Stacewicz-Sapuntzakis M. Dried plums and their products: composition and health effects—an updated review. Crit Rev Food Sci Nutr
8. Yao CK, Tan HL, van Langenberg DR, et al. Dietary sorbitol and mannitol: food content and distinct absorption patterns between healthy individuals and patients with irritable bowel syndrome. J Hum Nutr Dietet
. 2014;27(suppl 2):263–275.
9. Hyams JS. Sorbitol intolerance: an unappreciated cause of functional gastrointestinal complaints. Gastroenterology
10. EFSA Panel on Dietetic Products. Nutrition and Allergies (NDA); Scientific Opinion on the substantiation of health claims related to dried plums of ‘prune’ cultivars (Prunus deomistica
L) and maintenance of normal bowel habit (ID 1164, further assessment) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA J
11. Cheskin LH, Mitola AH, Ridore M, Kolge S, Hwang K, Clark B. A naturalistic, controlled trial of plum juice versus psyllium versus control for improving bowel function. Int J Nutr Wellness
12. Attaluri A, Donahoe R, Valestin J, Brown K, Rao SS. Randomised clinical trial: dried plums (prunes) vs. psyllium for constipation. Aliment Pharmacol Ther
13. Lucas EA, Hammond JL, Mocanu V, et al. Daily consumption of dried plum by postmenopausal women does not cause undesirable changes in bowel function. J Appl Res
14. Howarth L, Petrisko Y, Furchner-Evanson A, Nemoseck T, Kern M. Snack selection influences nutrient intake, triglycerides, and bowel habits of adult women: a pilot study. J Am Deit Assoc
15. Lever E, Scott SM, Emery PW, Whelan K. The effect of prunes on stool output, whole gut transit time and gastrointestinal symptoms: a randomized controlled trial. Proc Nutr Soc
16. Arjmandi BH, Lucas EA, Juma S, et al. Dried plums prevent ovarectomy-induced bone loss in rats. J Am Nutraceutical Assoc
17. Hooshmand S, Arjmandi BH. Viewpoint: dried plum, an emerging functional food that may effectively improve bone health. Ageing Res Rev
18. Shahnazari M, Turner RT, Iwaniec UT, et al. Dietary dried plum increases bone mass, suppresses proinflammatory cytokines and promotes attainment of peak bone mass in male mice. J Nutr Biochem
19. Léotoing L, Wauquier F, Davicco MJ, et al. The phenolic acids of Agen prunes (dried plums) or Agen prune juice concentrates do not account for the protective action on bone in a rat model of postmenopausal osteoporosis. Nutr Res
20. Rendina E, Hembree K, Davis MR, et al. Dried plum's unique capacity to reverse bone loss and alter bone metabolism in postmenopausal osteoporosis model. PLoS One
21. Arjmandi BH, Khalil DA, Lucas EA, et al. Dried plums improve indices of bone formation in postmenopausal women. J Womens Health Gend Based Med
22. Hooshmand S, Chai SC, Saadat RL, Payton ME, Brummel-Smith K, Arjmandi BH. Comparative effects of dried plum and dried apple on bone in postmenopausal women. Br J Nutr
23. Hooshmand S, Kern M, Metti D, et al. The effect of two doses of dried plum on bone density and bone biomarkers in osteopenic postmenopausal women: a randomized, controlled trial. Osteoporos Int
24. Schreurs AS, Shirazi-Fard Y, Shahnazari M, et al. Dried plum diet protects from bone loss caused by ionizing radiation. Sci Rep
*The Functional Foods for Health Program was a joint program between the Chicago and Urbana campuses of the University of Illinois that brought faculty and students from a variety of disciplines and industrial affiliates together for scientific meetings that included guest speakers and poster sessions and discussion groups. I was a founding member and I was the first Chicago campus faculty leader. At its peak, it had over 100 faculty and 35 industrial affiliates.
†The CDPB has written guidelines on treatment of applications for funds from current NAP board members. The same criteria are used for evaluation as any other proposal and board membersmay not be present during evaluation nor may they communicate with current board members concerning their proposal. This also covers submissions of protégés or colleagues of the proposal-submitting board member. This governing document is signed by all members of board each time the NAP convenes.
‡Sorbitol has Generally Recognized As Safe (GRAS) status and GRAS sets limits for percent that can be contained in specific food items but does not set a human limit. Very old references from 2 small studies find that ~20 g of pure sorbitol can produce diarrhea.Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.