RATIONALE: Dietary fat may be involved in the growth of cancer cells. Restricting dietary fat may help fight cancer.

PURPOSE: Randomized clinical trial to study the effectiveness of a low fat diet in treating postmenopausal women who have stage I, stage II, or stage IIIA breast cancer that has been completely removed by surgery.

OBJECTIVES: I. Determine whether dietary fat reduction will effectively prolong disease-free and overall survival in women surgically treated for early stage breast cancer who are receiving adjuvant therapy with or without either tamoxifen, cyclophosphamide, methotrexate, fluorouracil (CMF), doxorubicin, cyclophosphamide (AC), fluorouracil, doxorubicin, cyclophosphamide (FAC, CAF), or AC followed by paclitaxel. II. Evaluate whether differences in the lipid profile are associated with dietary group assignment and dietary fat.

OUTLINE: This is a randomized, multicenter study. Patients are stratified by center, nodal status, ER status, and type of adjuvant chemotherapy. The first group receives intensive dietary intervention for reduction of total fat intake to 15% of calories, with repeated individual and group counseling sessions. The second group receives USDA/DHHS dietary guidelines and minimal intervention. All patients who are estrogen receptor positive receive concurrent therapy with tamoxifen; cyclophosphamide, methotrexate, fluorouracil (CMF) followed by tamoxifen; doxorubicin, cyclophosphamide (AC) followed by tamoxifen; fluorouracil, doxorubicin, cyclophosphamide (FAC, CAF) followed by tamoxifen; or AC, paclitaxel followed by tamoxifen. Patients are followed annually throughout the study.

PROJECTED ACCRUAL: Approximately 2,500 women will be accrued for this study.

DISEASE CHARACTERISTICS: Histologically proven, invasive, localized carcinoma of the breast Stage I/II/IIIA disease, i.e.: Tumor confined to breast on clinical examination Overlying skin movable with respect to tumor Tumor movable in relation to underlying muscle and chest wall Bone scan and/or x-ray required to rule out bone metastases in cases of skeletal pain Tumor size requirements: No greater than 5 cm if lymph nodes are positive Greater than 1 cm if lymph nodes are negative Tumor definitively treated by one of the following procedures: Total mastectomy with axillary node dissection Segmental mastectomy with or without axillary node dissection and/or sentinel node biopsy followed by breast irradiation, provided: Surgical margins are histologically free of invasive or noninvasive tumor One additional resection allowed to obtain clear margins Total mastectomy required if clear margins are not obtained at second resection The following conditions exclude: Bilateral malignancy or any mass in the contralateral breast unless proven nonmalignant by biopsy Palpable lymph nodes in the contralateral axilla or probable supraclavicular or infraclavicular nodal involvement unless proven nonmalignant by biopsy 10 or more positive lymph nodes Inflammatory breast cancer Ulceration or erythema Infiltration of the skin or peau d'orange Tethering or dimpling of the skin or nipple inversion should not be considered skin infiltration Satellite breast nodules Parasternal nodules Edema of the arm Hormone receptor status: Any estrogen receptor (ER) or progesterone receptor (PR) status allowed ER assessment required PR assessment recommended Less than 365 days between definitive surgery and randomization

PATIENT CHARACTERISTICS: Age: 48 to 78 Sex: Female Menopausal status: Postmenopausal Performance status: Not specified Life expectancy: At least 10 years (excluding breast cancer) Hematopoietic: WBC at least 3,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 mg/dL AST no greater than 60 IU/mL (or within 2 times normal) Renal: Creatinine no greater than 1.5 mg/dL Cardiovascular: No active cardiac disease that would preclude doxorubicin in patients assigned to adjuvant chemotherapy with doxorubicin Other: Baseline caloric intake at least 20% fat Accessible for follow-up and by telephone Sufficient memory required to provide food recall data Must speak and read English Medically and nutritionally eligible for either dietary intervention arm No prior or concomitant malignancy except curatively treated nonmelanoma skin cancer or carcinoma in situ of the cervix

PRIOR CONCURRENT THERAPY: No concurrent participation in another adjuvant breast cancer trial that has disease-free or overall survival as a study endpoint (e.g., a major cooperative group trial) Biologic therapy: Not specified Chemotherapy: Concurrent adjuvant cyclophosphamide, methotrexate, fluorouracil (CMF), doxorubicin, cyclophosphamide (AC), AC followed by paclitaxel, or fluorouracil/doxorubicin/cyclophosphamide (FAC, CAF) allowed If ER negative, approved chemotherapy regimen and/or tamoxifen required No more than 120 days between definitive surgery and initiation of adjuvant systemic chemotherapy Endocrine therapy: Concurrent adjuvant tamoxifen required if ER positive (if ER negative, tamoxifen and/or an approved chemotherapy regimen required) No more than 180 days between definitive surgery and initiation of tamoxifen (if receiving tamoxifen alone) If receiving adjuvant CMF, AC, or FAC, CAF, or AC, paclitaxel, tamoxifen begins after completion of adjuvant therapy Radiotherapy: Radiotherapy required within 56 days following segmental mastectomy Surgery: Definitive surgery required Prior oophorectomy for reasons other than malignancy allowed