Filtered coffee consumption linked to improved blood sugar and healthier HbA1c levels: Study - Video

Your morning coffee might be doing more for your health than just waking you up-it could also be helping stabilize your blood sugar. A new study published in npj Science of Food has uncovered how unsweetened filtered coffee may support long-term glycemic control by improving the composition of the gut microbiome. Using advanced genetic tools, researchers traced this connection through a causal pathway involving a specific gut bacterium called Veillonella, which produces propionic acid-an important compound linked to better insulin sensitivity.

Understanding the relationship between coffee and metabolism has long puzzled scientists. While previous observational studies suggested coffee reduces type 2 diabetes risk, clinical trials have been inconsistent, partly because they rarely accounted for differences in how people prepare their coffee-filtered or instant, sweetened or black. To resolve these contradictions, researchers from China and the United Kingdom used Mendelian Randomization (MR), a genetic method that infers cause-and-effect relationships from natural variations in people’s DNA.

The study combined data from two large genetic repositories—the UK Biobank, which includes more than 500,000 participants, and the MiBioGen Consortium, which profiles gut bacteria in about 18,000 individuals. Researchers analysed six coffee consumption patterns (including with sugar, milk, or artificial sweeteners) and tested their links to glycated haemoglobin (HbA1c), a reliable marker of average blood glucose levels over 8–12 weeks.

Among all coffee types tested, only genetically predicted unsweetened filtered coffee showed a direct, statistically significant link with lower HbA1c levels (Odds Ratio = 0.97; p = 0.04). When the team looked deeper, they discovered that filtered coffee was associated with higher genetic abundance of the bacterium Veillonella, known for producing propionic acid, a short chain fatty acid that helps regulate glucose metabolism. Mediation analysis revealed that Veillonella explained about 43% of coffee’s glycaemic benefit. In contrast, adding sugar or artificial sweeteners appeared to blunt these positive effects.

The researchers propose that brewing methods matter because filtration removes diterpenes while preserving beneficial chlorogenic acids and polyphenols, which may create a gut environment favoring propionate producing microbes. Though more experimental research is needed, the findings suggest a practical takeaway: when it comes to blood sugar control, unsweetened filtered coffee might be the smartest brew to choose.

REFERENCE: Cao, Z., An, Y., Du, Y., Xu, G., Wang, J., & Lu, Y. (2025). Different coffee consumption patterns affect HbA1c via propionic acid-producing gut microbiota. NPJ Science of Food. DOI – 10.1038/s41538-025-00655-w. https://www.nature.com/articles/s41538-025-00655-w