Breast cancer affects one out of eight women in their lifetime. Many factors contribute to the development of breast cancer, such as hereditary mutations and lifetime exposure to environmental factors, including estrogen. In addition, overweight and obesity, especially with increased waist circumference, are known to be associated with breast cancer risk. This review will summarize our understanding of the effect of diet on breast cancer incidence and progression. Since some inflammatory cytokines that are changed by a high-fat diet are known to promote the growth of breast cancer cells, these cytokines may serve as biomarkers to monitor the dietary influence for women at high risk of breast cancer and as future therapeutic targets for breast cancer treatment.