New research in mice shows that both polyphenol and carbohydrate components of dried plums (Prunus domestica) have prebiotic activity characterized by alterations in the microbiota and increases in short chain fatty acids, and contribute to improved bone microarchitecture, however, their structural and metabolic effects on bone differ over time.

Smith et al. investigated the contribution of polyphenol and carbohydrate components of dried plums on a bone model of postmenopausal osteoporosis to explore their prebiotic activity. Image credit: Smith et al., doi: 10.3390/nu14091685.

Dried plums are a rich source of polyphenolic compounds and have high antioxidant capacity far exceeding even that of apples, strawberries, oranges, or grapes.

They are also rich in vitamins A, C, and E, and beta-carotene and various mineral compounds.

In previous studies, dried prunes have been found to stimulate favorable gut microbiota changes and to protect bone health. Those effects have largely been attributed to the polyphenolic compounds.

However, the exact mechanisms and contribution of other important nutrients, such as carbohydrates, have been unclear.

“Both the carbohydrate component and the polyphenols within the prunes altered the gut microbiota and were associated with positive effects on bone, namely restoring bone,” said Professor Brenda Smith, a researcher at the Indiana University School of Medicine.

“By definition, prebiotics are substrates that alter the composition or activity of the microbiota and confer benefits to the health of the individual.”

In the new study, Professor Smith and her colleagues isolated the polyphenol compounds as well as the carbohydrates from dried prunes and fed them to two separate groups of estrogen-deficient, female mice with substantial bone loss for 5- and 10-week durations

For comparison, three additional groups of the mice were assigned to diets either containing whole prunes, a prune crude extract with both polyphenol and carbohydrate components, or a diet consisting of no prunes or prune components, which served as the control group. All diets were comparable in macronutrients.

Compared to the mice who did not consume any prune or prune component, those who consumed isolated carbohydrates, isolated polyphenols, prune crude extract, or whole prunes experienced restored bone previously lost.

These mice also showed a significant increase in short chain fatty acid production in their guts, as well favorable changes to their gut microbiota.

In particular, the researchers saw increases in short chain fatty acids n-butyrate and propionate, which are thought to be most effective at preventing bone loss by suppressing biomarkers associated with bone breakdown.

These observations suggest that prunes and prune components may affect the gut in a manner that contributes to improved mineral absorption, immune system processes, and the gut barrier’s integrity — all of which can affect hormones, metabolites, and immune cells that play a role in bone health.

The researchers also reported that carbohydrates independently showed the ability to restore bone early in the study while the effect of polyphenols on bone became evident and more important later.

“Even though we think they’re both having prebiotic activity, those prebiotics are probably occurring by different mechanisms,” Professor Smith said.

“Our findings make a strong case for consuming whole prunes because you’re getting some of the benefit from the carbohydrate in the short term, and the long-term benefit from the polyphenols.”

“The vitamins, minerals, and plant compounds in prunes may also contribute to the bone and the gut benefits,” she added.

“This research gets us closer to understanding the unique attributes of prunes while underscoring the importance of eating the fruit in its entirety.”

The study appears in the journal Nutrients.

Brenda J. Smith et al. 2022. Dried Plum’s Polyphenolic Compounds and Carbohydrates Contribute to Its Osteoprotective Effects and Exhibit Prebiotic Activity in Estrogen Deficient C57BL/6 Mice. Nutrients 14 (9): 1685; doi: 10.3390/nu14091685