Abstract Background Many factors can identify the mortality risks of institutionalized elderly people; among all such factors, body mass index (BMI) and energy intake (EI) can be employed as independent predictors. The objective of this study was to elucidate about the mortality risks and the trajectory of two parameters obtained from continuously monitored data. Methods This retrospective cohort study targeted 218 elderly people who were admitted to a nursing home for at least 6 months between 2007 and 2020 and passed away at the nursing home. BMI and EI (kcal) per body weight (BW) were continuously measured until death. Results BMI continued to decrease for 5 years until death. The rate of change of BMI significantly increased for 3 years before death (P = 0.004). In contrast, the rate of change of EI per BW significantly increased after 1 year before death (P < 0.001); in addition, 2 months before death, this rate of change significantly exceeded that of BMI (P = 0.007). In the four risk groups that were examined, a BMI of