Abstract Background: Within oncology, nutrition and eating behaviors are often tied to cancer prevention, incidence rates, progression, and healthy survivorship, as well as symptom and side effect management. While many nutrition-related resources and guidelines focus on physical health outcomes, support around nutrition and eating behaviors can have critical implications for mental health and quality of life outcomes among breast cancer patients and survivors. Methods: 232 women with breast cancer enrolled in the online Cancer Experience Registry and provided sociodemographic and clinical characteristics, answered questions about their eating and nutrition experiences, including utilization of a Registered Dietitian for professional eating and nutrition support since being diagnosed with cancer, and completed the Patient-Reported Outcomes Measurement Information System (PROMIS-29v2.0 + 2-item Cognitive Function Short Form). Frequencies were calculated and group differences among those who wanted professional support for eating and nutrition but either did or did not receive it were assessed using independent-samples t-tests. Results: The sample was 81% Non-Hispanic (NH) White, 9% NH Black. Participants varied in age (mean=61 yrs; SD=9.2), time since diagnosis (median=7 yrs, range: < 1-39) and socioeconomic status (16% household income < $40K; 32% employer-provided insurance coverage). 44% were currently receiving treatment, with 70% in remission, 12% with metastatic disease, and 21% with history of recurrence. Over one-third (36%) received professional support for eating and nutrition from a Registered Dietitian since being diagnosed with cancer, including 12% receiving that support in the last 6 months. Participants wanted professional support for eating and nutrition during active treatment (51%), after treatment (44%), at initial diagnosis (23%), before treatment (18%), before being diagnosed with cancer (11%) . The most commonly reported eating and nutrition needs driving the desire for professional support included weight-related support (54%; maintenance, gain, or loss), achieving healthy eating patterns (52%), increasing energy level (46%) and physical fitness/strength (45%). However, experiences with professional support for eating and nutrition varied: 54% wanted eating and nutrition support since being diagnosed with cancer, but only 68% of those who wanted this support were able to access care. Irrespective of access to professional eating and nutrition support, participants report changing their eating patterns to manage SSEs (50%) or improve long-term health (57%). Among those who desired professional support for eating and nutrition since being diagnosed with cancer (n=102), those who did not get the desired support (n=34) compared to those who did (n=68) reported higher levels of anxiety, depression, sleep disturbance, and pain, as well as lower levels of physical and cognitive function (all ps < .05). Levels of fatigue and social function were not significantly different between groups. Conclusion: While there is a strong desire for professional support surrounding eating and nutrition among women with breast cancer, when that support is needed and what it aims to address varies greatly. Among those interested in receiving professional support for eating and nutrition, those who accessed professional support reported greater mental health and quality of life. Further research is needed to understand barriers to accessing eating and nutrition support among those who are not able to obtain it. Community-based advocacy organizations that offer access to professional support services for eating and nutrition are critical for addressing unmet needs in this area to improve health and well-being among women with breast cancer. Citation Format: Victoria Morris, Melissa Miller, Susan Weldon, Gail Kelly. Professional Support for Eating and Nutrition among Women Living with Breast Cancer: Implications for Mental Health and Quality of Life [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-10-09.