Methods: A comprehensive literature review spanning the past two decades was conducted to analyze the contributions of genetic variants—including FTO, MC4R, and LEPR—and their associations with dietary habits, highlighting how specific nutrients affect gene expression and obesity risk and how the coexistence of metabolic diseases such as type 2 diabetes and osteoporosis may modulate these factors. This evidence concerns the gene MC4R and obesity due to melanocortin 4 receptor deficiency.