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A recent randomized, double-blind, placebo-controlled trial from Japan has shed important new light on how blackcurrant extract may support gut health in athletes—especially those at risk of gut imbalances due to their intense training routines.
Athletes, particularly those in high-intensity sports like rugby, are known to experience unique gut health challenges. Frequent, hard training not only increases protein and carbohydrate requirements, but athletes may also intentionally restrict fiber to avoid digestive discomfort during play.
While some exercise is beneficial for the gut, extended intense training can contribute to “dysbiosis” - an imbalance in gut bacteria that may increase inflammation, gut permeability, and reduce resilience.
This new study recruited 88 healthy male university rugby players. None of the participants had diagnosed gastrointestinal issues, but as with many competitive athletes, a sizable number already showed evidence of gut microbial imbalance.
Over four weeks, the rugby players were split into four groups:
Placebo (maltodextrin)
Blackcurrant extract
Partially hydrolyzed guar gum (PHGG), a prebiotic fiber
A combination of blackcurrant extract and PHGG
The team collected fecal samples at the beginning and end of the study, also analyzing short-chain fatty acid (SCFA) levels, important indicators of gut health produced by beneficial bacteria.
Key Results: Small but Meaningful Shifts in the Microbiome
While overall gut microbiota structure remained relatively unchanged for most, the interventions led to notable changes in the abundance of certain beneficial bacteria. In particular, the blackcurrant extract and the combination group both saw increased levels of Megasphaera spp., helpful bacteria known to produce butyrate - a short-chain fatty acid with powerful anti-inflammatory effects.
For those athletes who started the study with signs of gut dysbiosis (the majority), all intervention groups showed significant increases in total fecal SCFA concentrations, regardless of whether they took blackcurrant, PHGG, or both.
This indicates that both blackcurrant extract and PHGG can enhance the metabolic activity of the gut bacteria - boosting the production of beneficial SCFAs like acetate and propionate - even if the actual types of bacteria don’t shift drastically.
Why Is This Important?
SCFAs are key to gut and whole-body health: they help maintain the gut lining, regulate inflammation, and even support energy metabolism. The finding that blackcurrant extract can improve SCFA production in athletes with gut imbalance is significant, as it suggests a simple, dietary way to counteract some of the negative effects of intensive sport on the gastrointestinal system.
No Statistically Significant Synergy - But Clear Independent Benefits
Interestingly, while the combination of blackcurrant and PHGG showed some positive results, the study didn’t find evidence that the two work better together than individually at the doses used. This may mean different dosages or timings are needed to achieve synergy.
Bottom Line
For hard-training athletes and those experiencing digestive complaints, blackcurrant extract appears to support a healthier gut environment, primarily through boosting the function (rather than the composition) of gut bacteria. As ever, further research in other populations and over longer supplementation periods will help clarify these findings, but this robust new study points to a practical nutritional strategy for athletes seeking to protect their gut and optimize long-term health.
Reference
Miura, H.; Oda, M.; Abe, K.; Ikeda, H.; Fujibayashi, M.; Oda, N.; Segawa, T.; Abe, A.; Ueta, N.; Tsukahara, T.; et al. Effects of Blackcurrant Extract and Partially Hydrolyzed Guar Gum Intake on Gut Dysbiosis in Male University Rugby Players. Microorganisms 2025, 13, 1561. https://doi.org/10.3390/microorganisms13071561
