Obesity is a poor prognostic factor and is negatively related to quality of life (QOL) in breast cancer survivors. Exercise and Nutrition to Enhance Recovery and Good Health for You is the largest weight loss trial completed among cancer survivors. Percent losses in body weight with an intensive group-based intervention versus an attention control were 6.0 versus 1.5 % (p < 0.0001) and 3.7 versus 1.3 % (p < 0.0001) at 12 and 24 months, respectively. ENERGY also was designed to answer the research question: Does weight loss significantly improve vitality and physical function (key components of QOL)? 692 breast cancer survivors (BMI: 25–45 kg/m2) at 4 US sites were randomized to a year-long intensive intervention of 52 group sessions and telephone counseling contacts versus a non-intensive (control) of two in-person counseling sessions. Weight, self-reported QOL, and symptoms were measured semi-annually for two years. Significant decreases in physical function and increases in symptoms were observed among controls from baseline to 6 months, but not in the intervention arm, −3.45 (95 % Confidence Interval [CI] −6.10, −0.79, p = 0.0109) and 0.10 (95 %CI 0.04, 0.16, p = 0.0021), respectively. Improvements in vitality were seen in both arms but trended toward greater improvement in the intervention arm −2.72 (95 % CI −5.45, 0.01, p = 0.0508). These differences diminished over time; however, depressive symptoms increased in the intervention versus control arms and became significant at 24 months, −1.64 (95 % CI −3.13, −0.15, p = 0.0308). Increased QOL has been reported in shorter term diet and exercise trials among cancer survivors. These longer term data suggest that diet and exercise interventions improve some aspects of QOL, but these benefits may diminish over time.