The dissertation's three research papers examined the following issues in breast cancer survivors (a) the effect of adjuvant therapy on significant relative weight gain after cancer diagnosis and whether those participants gaining weight return to pre-cancer weight during follow- up, (b) the effect of dietary intervention on weight over time, and (c) the role of dietary energy density on weight over time. The data came from a large, multi-site trial that randomized 3088 women, followed them for 6 years, and encouraged its intervention participants to consume a high fiber and low fat diet. At baseline and at follow-up visits weight and height were measured, dietary intake was assessed by 24-hour dietary recall and validated with plasma carotenoids concentrations, and demographic and physical activity data were obtained through questionnaire. Cancer stage and treatment modalities were obtained by medical record review. Paper I was cohort in design and included 3088 participants. Weight gain of & amp;#61619; 5% body weight following cancer diagnosis was considered significant. Chemotherapy was significantly associated with weight gain and Tamoxifen was not. Tamoxifen did not modify the effect of either chemotherapy or its different regimens on weight gain. Weight gain occurred irrespective of types or regimens of chemotherapy. Only 10% of participants returned to their pre-cancer weight at the follow-up visits. Paper II included 1510 overweight and obese participants and analyzed data adopting randomized design. Intervention participants consumed significantly more fruit, vegetables, and fiber, and less energy from fat than controls during follow-up. Body weight and obesity incidence did not differ between study groups at any follow-up visit. Paper III utilized randomized design to analyze data and included 3088 participants. Dietary energy density among intervention participants, irrespective of calculation method, decreased significantly compared to controls and was maintained over the follow-up period. Total energy intake or physical activity did not vary between the groups. Weight change between study groups was significant, albeit small, by one year and not afterwords. Return to initial weight following weight gain is unlikely. Dietary modification or dietary energy density reduction alone is not sufficient to promote long-term weight loss in a free- living populatio
