Sarcopenia and sarcopenic obesity (SO) represent significant age-related muscular disorders. Their specific biomarkers and pathophysiological mechanisms remain insufficiently elucidated. This study aims to identify differential and shared biomarkers between these conditions to reveal distinct pathophysiological processes, providing a foundation for precision diagnostics and targeted interventions. We conducted a systematic review and meta-analysis of studies examining biomarkers related to sarcopenia and SO in adults aged 45 and older. Electronic and manual searches were performed in PubMed, Web of Science, Cochrane Library, and Embase up to December 2024. The quality of each study was assessed using the National Institutes of Health Quality Assessment Tool. Meta-analysis was performed when at least three studies investigated the same biomarkers in frailty and sarcopenia, calculating the pooled effect size based on the standard mean difference using a random effects model. In total, 80 studies (64 on sarcopenia and 16 on SO) were included, encompassing 36,680 older adults (aged 45 and above) from 16 countries with varying levels of development. Participants were categorized based on their setting, age, and gender distribution. Sarcopenia is characterized by lower serum triglycerides and stable HDL/LDL ratios, while SO presents with higher triglycerides and disrupted cholesterol correlation, indicating distinct metabolic interactions. Analysis of inflammatory profiles revealed significantly elevated CRP levels in SO, with WBC as a specific marker, while TNF-α was associated with sarcopenia, suggesting a subtype-specific role of chronic inflammation. Vitamin D deficiency is prevalent in both conditions and may represent a potential therapeutic target. Subgroup analyses indicated an increased risk of muscle function decline in high-risk communities in developing regions, underscoring the urgent need for early intervention. A set of shared metabolic, hematologic, and inflammatory biomarkers was identified in sarcopenia and SO. These findings address a knowledge gap in biomarker research and highlight the distinct mechanisms involved in the development of both conditions. Developing biomarker-based diagnostic algorithms is essential for optimizing personalized treatment. Subgroup analyses have also identified high-risk populations, underscoring the need for early intervention.

Background/Objectives: This study aimed to investigate the effects of fish oil-derived omega-3 polyunsaturated fatty acids (omega-3 PUFAs) on gut microbiota and serum lipid metabolites in T2DM. Methods: In a three-month, randomized, double-blind, placebo-controlled study, 110 T2DM patients received either fish oil (n = 55) or corn oil (n = 55) capsules daily. Serum lipids, glycemic parameters, gut microbiota diversity, and lipidomics were assessed. Results: This study found that fish oil-derived omega-3 PUFAs intervention did not significantly lower the fasting plasma glucose levels when compared with the baseline level (p > 0.05). However, serum fasting blood glucose (p = 0.039), glycosylated hemoglobin levels (p = 0.048), HOMA-IR (p = 0.022), total cholesterol (p < 0.001), triglyceride (p = 0.034), LDL cholesterol (p = 0.048), and non-HDL levels (p = 0.046) were significantly lower in the fish oil group compared with the corn oil group after three months of intervention. Also, it altered glycerophospholipid metabolism and gut microbiota. After three months, the fish oil group showed a significantly lower abundance of Desulfobacterota compared with the corn oil control group (p = 0.003), with reduced levels of Colidextribacter (p = 0.002), Ralstonia (p = 0.021), and Klebsiella (p = 0.013). Conversely, the abundance of Limosilactobacillus (p = 0.017), Lactobacillus (p = 0.011), and Haemophilus (p = 0.018) increased significantly. In addition, relevant glycolipid metabolism indicators showed significant correlations with the altered profiles of serum lipid metabolites, intestinal bacteria, and fungi. Conclusions: This study highlights the impact of fish oil-derived omega-3 PUFAs on intestinal microbiota structure and function in patients with type 2 diabetes. The observed decrease in pathogenic bacterial species and the enhancement of beneficial species may have significant implications for gut health and systemic inflammation, both of which are pivotal in managing diabetes. Further research is warranted to comprehensively elucidate the long-term benefits and underlying mechanisms of these microbiota alterations.