In this narrative review, we synthesize current epidemiological and mechanistic evidence on the association between ultra-processed food (UPF) consumption, obesity, and breast cancer (BC) risk. The global increase in UPF intake has been linked to substantial metabolic alterations, including weight gain, insulin resistance, low-grade chronic inflammation, and hormonal imbalances—factors that contribute to a tumor-promoting microenvironment. Given the established role of obesity in breast carcinogenesis, understanding the intermediary role of UPFs is critical. Articles were selected from PubMed, SciELO, and ScienceDirect databases using descriptors related to ultra-processed foods, obesity, and breast cancer. The synthesis of current evidence supports the view that excessive UPFs consumption represents a modifiable and preventable risk factor for obesity and BC, underscoring the need for integrated strategies in dietary guidance, public health policy, and cancer prevention.