Is HbA1c useful for gut health?

HbA1c is a long-term blood sugar marker reflecting average glucose levels over the past 2–3 months. It is primarily used for diabetes diagnosis and monitoring. A link to gut health exists indirectly: the gut microbiota influences glucose metabolism via short-chain fatty acids, inflammation, and the gut-brain axis. Studies show that higher microbial diversity and certain bacteria (e.g., Akkermansia muciniphila) are associated with lower HbA1c levels. However, HbA1c is not a direct marker of gut health. It does not measure microbiome composition, gut barrier integrity, or inflammatory markers like calprotectin. For assessing gut health, stool tests (microbiome analysis, calprotectin, zonulin) or blood tests (hs‑CRP, lipopolysaccharides) are more appropriate. The evidence for a causal link between HbA1c and gut health is mostly mechanistic and observational. Therefore, HbA1c alone is not useful as a gut health indicator, but it can play a complementary role within a comprehensive metabolic and microbiome check.