Inclusion Criteria:

- Post-menopausal woman with a diagnosis of invasive breast cancer (T1-3,pN0-2,M0) for
which definitive surgery was performed during the previous 36 months.

- On adjuvant hormonal therapy with letrozole at time of randomization (either as
initial adjuvant hormonal therapy or after a switch from tamoxifen or other hormonal
therapy).

- BMI ≥ 24 kg/m2.

- Medical, surgical or radiation oncologist agrees to subject participation in a diet
and physical activity program.

Exclusion Criteria:

- Life expectancy less than five years.

- Self-reported inability to walk at least 2 blocks (at any pace).

- Insulin requiring diabetes (telephone directed diet and physical activity changes
would be difficult in this population without close coordination with the treating
physician). Non-insulin requiring diabetics are eligible for the study.

- Serious digestive and/or absorptive problems, including inflammatory bowel disease
and chronic diarrhea that preclude adherence to the study diet.

- Cardiovascular, respiratory or musculoskeletal disease or joint problems that
preclude moderate physical activity. Moderate arthritis that does not preclude
physical activity is not a reason for ineligibility.

- Psychiatric disorders or conditions that, in the opinion of the investigator, would
preclude participation in the study intervention (e.g. untreated major depression or
psychosis, substance abuse, severe personality disorder).

- Patients on aromatase inhibitors other than letrozole at study entry.

- Known recurrence of breast cancer (local, regional or distant) at any time prior to
study entry.

- History of other malignancies except: adequately treated non-melanoma skin cancer,
curatively treated in situ carcinoma of the cervix, or other solid tumours curatively
treated with no evidence of disease for ≥ 5 years. Prior in situ cancer of the breast
is not a reason for exclusion.

- Patients not fluent in either English or French (spoken and written).

- Patient unwilling or unable to provide informed consent.