Prunes, Prunes – They’re Good For Your Bones

Gratitude to my wife (and office manager) for sharing this interesting study, published in 2022, with me. 

Researchers at Penn State University randomly assigned 235 post-menopausal women to either eat 50 grams of prunes (aka dried plums) or not every day for a year. For context, 50 grams of prunes is about six prunes per day. After a year, they found that the women eating the prunes had better bone mineral density, and an accordingly lower estimated risk for bone fractures, than the women who weren’t. 

In other words, doing absolutely nothing other than adding six prunes per day to your diet might be a tool to keep your bones healthy, at least in post-menopausal women. 

You can read the full paper by clicking here.

Now as I usually do in research reviews, let me unpack this study a bit and examine its strengths and weaknesses. 

In terms of strengths:

• This was a randomized control trial, meaning a true experiment in which we can be reasonably certain that the only meaningful difference between the experimental group and the control group is that one was eating prunes and the other was not. Hence, it appears that the better bone health really was due to prune consumption, not some other unaccounted for variable. 
• When I first read the study, I wondered if there was something unique about prunes, or if any fruit (fresh or dried) would have had the same effect, but when I dug a bit deeper, it turns out the authors of this study were building on prior research in mice that indicated prunes have a compound in them that is uniquely protective against bone loss as compared to other fruits. This fact both strengthens the results (because they make sense in the context of what other studies have shown) as well as provide some helpful clinical information for patients (because we can be somewhat assured that there really is something unique to prunes, as opposed to other fruits, that is helpful for bone health). 
• The intervention itself is quite obviously a low-risk one. Meaning that if based on this study you were to start eating six prunes per day and it didn’t help your bones, there wouldn’t be much of a down side. Unlike with pharmacologic treatments, the cost and side effects of eating prunes would be pretty minimal, and there may be other benefits to prune consumption (fiber, polyphenols, etc) that would in other ways improve your health. Obviously, as with any medical intervention, you need to consult your own doctor and use your own judgement. Perhaps you hate prunes; have an allergy to them; find they give you digestive distress; or are a type 2 diabetic who gets very high blood sugar responses to eating dried fruit. In any of these cases, prunes may not be a good idea for you. But for the average person, adding prunes to their diet is unlikely to cause any major problems. 

Now onto some limitations of the study:

• Follow up was only for one year, but in the real world, bone loss is a decades long process. We can’t state with certainty that if the women in this study ate prunes for the next 10, 20, or 30 years, that they would continue to enjoy better bone health as a result. 
• Like a lot of studies, the studied outcome was a lab measurement (in this case a bone density scan, as well as some blood work), not the actual outcome we ultimately really care about, which would be a reduction in bone fractures. Studies are often done this way because it’s easier, quicker, and less expensive to study this kind of outcome, rather than waiting years and years to see who gets a fracture and who doesn’t. And while it’s somewhat reassuring that the women who ate prunes in this study had measurable improvements in their bone density, we can’t with absolute certainty state that this will translate to a reduced risk of fractures in the real world. 
• The effect size was not huge, meaning that the prune eaters had a modest improvement in bone density as compared to the non-prune eaters. There’s nothing in this study that makes me think that ONLY eating prunes (and skipping other interventions such as resistance exercise, adequate vitamin D, and potentially medications) would be a wise strategy to prevent or treat osteoporosis. 
• Finally, it’s worth noting that the study – surprise – was funded by the California Prune Board. This doesn’t mean the study is unreliable, nor that there is a “big prune” conspiracy. In the real world, doing scientific research is expensive, and it makes sense that big business interests who have the money to fund science will use that money to fund scientific research that may help their bottom line. There are mechanisms in place to ensure that the funders of research cannot simply fudge data to make the results of a study say what they want it to. But we also shouldn’t be naive to the fact that there may be subtle pressures for scientists to not “bite the hand that feeds them,” and if we are going to (justly) be concerned about the influence of big pharma on research studies that they fund, we should apply the same standard of skepticism when a study founded by a group of prune farmers funds research showing that prunes are especially helpful. 

As always, please don’t use this blog as a substitute for medical advice. Use your own judgement and consult your own physician if you have questions or concerns. But if you are concerned about osteoporosis, it may be reasonable to start incorporating regular prune consumption into your diet as part of your bone health strategy.