Dietary indices, gut microbiota, and CKM syndrome: From cross‐sectional signals to clinical meaning

We read with great interest the article by Zhang et al., Association between the Dietary Index for Gut Microbiota and Advanced Cardiovascular Kidney Metabolic Syndrome among United States Adults: A Cross-Sectional Study, published in JPEN.1 In a large, nationally representative cohort of 14,406 adults from NHANES, the authors describe a consistent inverse association between higher Dietary Index for Gut Microbiota (DI-GM) scores and advanced stages of cardiovascular kidney metabolic (CKM) syndrome. The findings resemble what one might observe when viewing urban traffic from above: areas designed with smoother infrastructure tend to function better, even if the aerial view cannot reveal which single modification resolved congestion. Likewise, higher DI-GM scores are associated with lower odds of advanced CKM, yet the cross-sectional design inherently limits causal inference and temporal interpretation.1 The study is timely, particularly as CKM is increasingly conceptualized as a progressive, interconnected condition linking metabolic dysfunction, inflammation, cardiovascular disease, and renal impairment.2, 3 We also commend the authors for adopting a diet quality index grounded in microbiota-related evidence rather than relying solely on conventional dietary scores.4 Several points may further contextualize the interpretation. Dietary intake derived from repeated 24-h recalls remains susceptible to both recall bias and reverse causation, as individuals with more advanced CKM may have already altered their eating habits.1, 5 In addition, constructing DI-GM categories using sex-specific medians may reduce sensitivity to clinically meaningful exposure gradients. Finally, while DI-GM reflects dietary patterns associated with microbial composition, it does not directly measure the gut microbiome. Without parallel microbiome or metabolomic data, distinguishing microbiota-mediated effects from those of an overall healthier dietary lifestyle remains challenging.6 Prospective studies incorporating longitudinal dietary assessments, dynamic CKM staging, and microbiome-derived intermediates could help translate this epidemiologic signal into clinically actionable insight. Such an approach may clarify whether DI-GM can ultimately serve not only as an associative marker but also as a practical guide for CKM risk modification. The authors have nothing to report. The authors declare no conflicts of interest. None. Not applicable. This Letter to the Editor does not include original data involving human participants or animals.