Critical synthesis of the diet–microbiota–inflammation–metabolic axis.
| Biological domain | Evidence | Interpretive limitation | Relevance to precision nutrition |
|---|---|---|---|
| Dietary exposure | Refined carbohydrates, saturated fats, and ultra-processed foods are associated with inflammatory and metabolic abnormalities, whereas fiber-rich and plant-based patterns are generally associated with more favorable profiles. [54–57] | Associations vary with adiposity, physical activity, medication exposure, baseline metabolic status, and other host factors. | Interpret dietary effects within host and metabolic context. |
| Microbial function and barrier integrity | Altered microbial function and intestinal barrier integrity may modify exposure to microbial-derived immune signals. [58, 59] | Microbial changes may precede, follow, or accompany inflammation; directionality remains uncertain in humans. | Functional microbiome and barrier measures may complement inflammatory assessment. |
| Microbial-derived inflammatory signals | LPS from Gram-negative bacteria has been implicated in inflammatory pathways relevant to metabolic dysfunction. Barrier disruption may increase exposure to microbial-derived molecules. [7, 8, 60] | Circulating LPS does not necessarily reflect biologically active gut-derived endotoxin, and its causal contribution to metabolic inflammation in humans remains uncertain. | Circulating LPS should not be interpreted as a standalone marker of gut-derived inflammation. |
| Inflammation and cellular stress | Nutrient excess and metabolic overload can increase reactive oxygen species and impair mitochondrial function; inflammatory signaling may further affect mitochondrial activity and insulin signaling. [61, 62] | Experimental evidence supports these interactions, but their temporal sequence and initiating role in human disease remain uncertain. | Interpret inflammatory measures alongside oxidative, mitochondrial, and metabolic measures. |
| Metabolic and cardiovascular outcomes | Persistent inflammatory activity is associated with impaired insulin sensitivity, altered lipid metabolism, obesity-related complications, and cardiovascular dysfunction. [63, 64] | Inflammatory markers may represent different processes across tissues and disease stages. | Consider tissue context and metabolic phenotype when interpreting biomarkers. |
| Biomarker interpretation | Inflammatory changes after dietary intervention may accompany changes in microbial function, energy balance, adiposity, or other metabolic processes. [65] | Association does not establish that a biomarker drives disease progression or represents a modifiable target. | Evaluate biomarkers against functional and clinically relevant metabolic outcomes. |
| Clinical evidence | Longitudinal human studies and controlled nutritional interventions are needed to determine whether inflammatory changes accompany or contribute to metabolic improvement. [65, 66] | No consistent initiating inflammatory pathway has been established across individuals or disease contexts. | Clinical application requires reproducible biomarkers and evidence of meaningful metabolic benefit. |
Evidence supports links among dietary exposure, microbial function, inflammatory signaling, cellular stress, and metabolic outcomes, but does not establish a uniform causal sequence. Interpretation depends on host phenotype, tissue context, metabolic status, and clinical outcomes. These limitations favor context-specific precision nutrition over reliance on individual biomarkers.