The purpose of this study is to measure the impact of an educational program to raise awareness of the increased spending energy in two different population of patients with breast cancer by using the questionnaire POPAQ (Population Physical Activity Questionnaire). This is a prospective study including two groups of 15 consecutive breast cancer patients (≤ 50 years Group 1 and Group 2 > 50 and < 70 years) followed in the department of radiotherapy at the Institute of Cancer of the Loire from January to July 2011. A questionnaire of physical activity assessment was used at two different times before the diagnosis/treatment of breast cancer (t0) and at 6 months (t6) to measure the impact of the awareness method. Comparison of different measures of daily energy expenditure (t0) between groups 1 and 2 was statistically significant (1,1803 and 9434 kJ/24 h, respectively, p = 0.0005). Daily energy expenditure of professional activity was statistically different between the two groups (1437 and 457 kJ/24 h, in groups 1 and 2, respectively; p = 0.003). Between t0 and t6, we observed a significant decrease in total energy consumption in group 1 (1,1803 to 1,0876 kJ/24 h) while there was no significant change between the group 2, except energy expended at rest (basal metabolism). There were differences in daily energy expenditure based on age may influence behavioral patterns deal with energy expenditure in physical activities. Tomorrow's challenges are to provide re-entrainment programs tailored to targeted populations.