I’ve been ignoring cherry juice for over a decade now. Studies continue to pop up in my network of potentially interesting research, suggesting that sour cherries accelerate post-exercise recovery, most often funded by the Cherry Marketing Institute. But other studies find no benefit. And more generally, my approach to integrating research is to assume that (a) nothing works and (b) if something really works in a meaningful way, you won’t have to look for evidence because everyone will be talking about it.
Cherry juice has not yet reached the “everyone’s talking about it” stage, at least in my circles, but studies keep coming, including a couple of recent reviews and meta-analyzes. Interestingly, the gist of some of these recent articles is less “Does Cherry Juice Work?” and more “We know cherry juice works, so why aren’t athletes using it anymore?” With that in mind, I’ll try to summarize the current state of research, then offer some reflections on why athletes might – and perhaps should – remain hesitant.
The best starting point is a meta-analysis published last year in International Journal of Sports Nutrition and Exercise Metabolism by Jessica Hill of St. Mary’s University and her colleagues. Hill’s team combined the results of 14 studies with a total of 303 subjects, looking at recovery from strenuous exercise. They found evidence of a “small beneficial effect” on muscle pain, a “moderate beneficial effect” on muscle strength recovery, and mixed effects on blood markers of muscle damage and inflammation.
This sounds pretty good. But if you dig deeper into the results of individual studies, you find many results that cluster around zero and some outliers, usually the ones with the largest error bars, which are strongly positive. It doesn’t fill me with much confidence.
Here is an illustration of what I mean. This is called the “forest plot,” with every single result in the study represented by a horizontal line and the overall mean shown by a diamond. Lines or diamonds to the left of the vertical line indicate that cherry juice aided strength recovery after harmful exercise; the lines or diamonds on the right indicate the opposite. The wider the horizontal line, the larger the error bar. The studies above focus on “metabolic” exercises such as endurance cycling; the studies below focus on “mechanical” exercises such as lifting heavy weights. I realize this sounds too complicated, but it’s a great way to get an overview of an entire body of research:
Again, these were the data for strength recovery, which had the most positive effect of all outcome variables in the meta-analysis. What catches my eye are four highly positive studies, which, on closer inspection, turn out to be a single Connolly study in 2006, with four results measured at 24, 48, 72 and 96 hours. Remove that study and I suspect the overall “moderately beneficial” effects would largely vanish. (And yes, for the record, the Connolly study was funded by Cherrypharm, a cherry juice company, and the three study authors each had a stake in the company.)
So, to sum it up, this meta-analysis did not eliminate my skepticism when it was published last year. What caught my eye, however, was a more recent review in Scandinavian Journal of Medicine and Science in Sports by Malachy McHugh of the Nicholas Institute of Sports Medicine and Athletic Trauma in New York (and, apparently, co-author of the 2006 Connolly study).
McHugh’s article offers a great overview of the arc of sour cherry research. Why, for example, do you focus on sour cherries rather than sweet ones? It’s simply a matter of cost and availability – they both work similarly, but the Montmorency Cherry Tart industry in Michigan provides an affordable supply. There are juices, gels and powders, which seem to work. A typical serving is the equivalent of around 100 fresh cherries per day. And there’s a key misunderstanding that could explain some of the study’s conflicting results, says McHugh: Cherry juice is really a “precocious” drink rather than a recovery drink. It takes several days of supplementation to strengthen your defenses against exercise-induced muscle damage, so take cherry juice after Exercise is unlikely to help.
This is the idea that caught my attention and ultimately inspired me to take a dip in the cherry juice literature. The key ingredient in sour cherries are their anthocyanins, which are responsible for the red, blue and purple color of cherries, blueberries, grapes and various other foods. Anthocyanins have both antioxidant and anti-inflammatory properties, which is why they could help the body deal with the heavy oxidative and inflammatory impact of hard exercise.
According to a survey of athletes from 15 countries in 21 sports published last year, 22.6% of respondents had used or were using cherry juice supplements. I’d be wary of taking that number too literally, because when a group of cherry juice researchers recruit subjects “through social media and posters,” you have to wonder if the people they reach might be more likely than average to have heard of cherry. juice. The real reason I am citing this study is that one of the 21 sports covered was “weaselling”, which to my disappointment appears to be a quintessentially British cross between bouldering and caving rather than literally chasing live weasels.
As I said above, new studies keep popping up. There was one released just this month by the University of Exeter that shows a nice improvement in strength recovery after exercise after seven days of loading tart cherry concentrate. Other studies published this year look at mental fatigue and mood, blood pressure, and blood sugar control. It’s easy to get excited about the potential benefits, but the overall results remain stubbornly ambiguous. And there are also methodological problems: for example, some studies require participants to limit the consumption of foods rich in anthocyanins in the days leading up to the experiment. Perhaps a normal balanced diet gives you all the anthocyanins you can use, and the benefits only manifest themselves if you create an artificial deficiency.
While the evidence was crystal clear that cherry juice accelerates recovery, there is a more fundamental question. Anthocyanins are part of a larger body of antioxidant and exercise research that remains highly controversial, as a recent review explains. As with cherry juice, there is some suggestive but ambiguous evidence that antioxidants in general can aid recovery. But there is a parallel stream of research that suggests that antioxidant supplements interfere with the gains you would normally get from both aerobic and endurance training. Reactive oxygen species that produce oxidative damage are also important signaling molecules, which tell the body to adapt and become stronger in response to exercise. Neutralize them with antioxidants and you may feel better tomorrow but be less fit next week or next month.
To be clear, the practical relevance of this research is still under debate. One school of thought argues that you should use antioxidants before major competitions when recovery is your top priority, but avoid them during intense training when the main focus is on increasing fitness. In theory it sounds like a good idea, but I don’t think anyone has proven that it leads to better real-world performance.
The problem with cherry juice research, generously funded by the cherry industry, is that there is little incentive to consider potential indirect negative effects. I realize there is a bit of a catch-22 for supplement companies: if they don’t fund research, they are criticized for selling unscientific products; if they fund research, they are criticized for distorting the literature. So, for the record, I think it’s great that cherry growers are funding good independent studies, even if the results haven’t convinced me.
I am also a huge fan of cherries. I always keep a bag in the freezer for cereal toppings and smoothies, and I especially like the sour cherries from my neighbor’s tree. I also frequently love and consume other foods rich in anthocyanins such as blueberries and saskatoon berries. I think they are tasty and healthy. But for me, there is a big step from consuming a food to consuming a processed extract or concentrate of that food with the goal of increasing performance. To make that leap, I’d like to see clear, unambiguous evidence that you earn more than you lose, and for the black cherry juice, I’m still waiting.
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