PURPOSE: Obesity and diet quality are two distinct lifestyle factors associated with morbidity and mortality among breast cancer survivors. The purposes of this study were to examine diet quality changes during a weight loss intervention among breast cancer survivors and to examine whether diet quality change was an important factor related to weight loss.METHODS: Participants were overweight/obese breast cancer survivors (n = 180) participating in a weight loss intervention. Diet quality scores were calculated using the Healthy Eating Index (HEI)-2010. Paired sample t-tests were run to examine change in diet quality, and a latent difference model was constructed to examine whether change in diet quality was associated with weight change.RESULTS: Participants significantly improved diet quality (P = 0.001) and lost 13.2 ± 5.8% (mean ± SD) of their weight (P = 0.001). Six-month HEI score was significantly associated with weight loss, controlling for baseline BMI (P = 0.003). Improvement in diet quality was also significantly associated with weight loss (P = 0.01).CONCLUSION: Our findings indicate that a weight loss intervention can result in both clinically significant weight loss and improvement in diet quality, and that improved diet quality is predictive of weight loss. Both weight loss and diet quality are implicated in longevity and quality of life for breast cancer survivors.