A large meta-analysis of breast cancer studies reported that obesity in premenopausal women is a positive risk factor for triple-negative breast cancers (TNBC, odds ratio (OR) 1.4–3.7) but a negative risk factor in estrogen receptor (ER) positive breast cancers (OR 0.35–0.81) [43]. This evidence concerns the gene ESR1 and obesity due to melanocortin 4 receptor deficiency.