Mutual Impact of Dietary Antioxidants and TNF-α rs1800629 on Insulin Levels in Adults with Obesity

Background/objectives: The interplay between genetic factors and nutritional patterns is critical in understanding metabolic health. This analysis evaluated the potential reciprocal relationships between the TNF-α -308 G/A gene polymorphism, the Composite Dietary Antioxidant Index (CDAI), and insulin-related variables in Spanish adults with obesity. Methods: A cross-sectional analysis was conducted in 292 adults with obesity. Anthropometric, biochemical, and dietary variables were assessed. TNF-α -308 G/A genotyping was performed. Associations and potential interactions between CDAI and genotype on insulin and homeostatic model assessment for insulin resistance (HOMA-IR) were examined using multivariate regression and two-way ANOVA. Results: Higher CDAI scores were significantly associated with lower insulin levels (p < 0.001) and HOMA-IR (p < 0.001), regardless of genotype. Carriers of the A allele (GA/AA) showed a non-significant trend toward higher insulin levels (p = 0.087) and a steeper decrease in insulin levels with increasing CDAI, with a significant interaction observed between TNF-α genotype and CDAI (interaction p = 0.003). Multivariate analyses confirmed that CDAI and TNF-α genotype were independently associated with insulin and HOMA-IR levels. However, interaction terms were not consistently significant across all models. Conclusions: These findings emphasize the potential of antioxidant-rich diets to help modulate the influence of pro-inflammatory genotypes on insulin resistance, highlighting the relevance of integrating genetic and dietary factors in managing obesity-related metabolic risks. Further studies are warranted to confirm these preliminary findings and to better understand the mechanisms underlying gene–diet interactions in metabolic regulation.