Decaf May Improve Memory Where Caffeinated Coffee Did Not, Small Study Suggests

Decaffeinated coffee may lack the familiar buzz, but a small randomized experiment suggests it could have a surprising cognitive edge over caffeinated coffee—possibly through effects on the gut microbiome.

Researchers led by stress neurobiologist John Cryan of University College Cork report in Nature Communications that only participants who resumed drinking decaffeinated coffee showed measurable gains on two memory tests; those who drank caffeinated coffee did not. The team proposes that coffee components other than caffeine—particularly polyphenols—may feed gut microbes and trigger biological signals that reach the brain.

Study design and main findings

The trial enrolled 31 regular coffee drinkers who typically consumed about three to five cups a day. Participants stopped drinking coffee for two weeks, a withdrawal that produced substantial shifts in their stool microbiome profiles. After that washout, they were randomly assigned, in a double-blind protocol, to receive either decaffeinated or caffeinated instant coffee. Over the next three weeks they consumed four servings per day.

Reintroducing coffee—whether decaf or caffeinated—prompted rapid changes in gut-microbiome composition and was associated with reduced self-reported stress, lower symptoms of depression, and less impulsivity. However, certain effects differed by coffee type: the caffeinated group experienced reduced anxiety and improved attention and vigilance, while only the decaf group showed significant improvements on two memory measures (a word-list learning test and a location-memory test).

"Coffee is more than just caffeine – it's a complex dietary factor that interacts with our gut microbes, our metabolism, and even our emotional well-being," Cryan says. "Our findings suggest that coffee, whether caffeinated or decaffeinated, can influence health in distinct but complementary ways."

Possible mechanisms

Although caffeine acts directly on the brain, coffee contains more than a thousand other compounds. Many are polyphenols—plant-derived molecules that are not probiotics themselves but can feed and reshape the gut microbial community. The authors hypothesize that polyphenol-driven changes in microbial metabolism may produce metabolites or immune signals that influence cognition and mood.

Limitations and next steps

The investigators emphasize that this is a small, preliminary study and that its findings require replication in larger, more diverse samples. The trial cannot yet determine the precise biological pathways linking decaffeinated coffee to improved memory, nor can it exclude other contributing factors. Future research should measure specific microbial metabolites, extend follow-up, and test different doses and types of coffee.

Bottom line

This study adds to growing interest in how diet, gut microbes, and brain function interact. It suggests that decaffeinated coffee—via noncaffeine compounds such as polyphenols—may influence memory in ways that caffeinated coffee does not, while caffeine still appears to have distinct benefits for anxiety and attention. The results are intriguing but preliminary; they point to promising directions for further research rather than definitive dietary advice.

The full study is published in Nature Communications. Interviews and commentary cited are from the researchers involved in the trial.