Continuous high-soy protein soymilk intake affects ordinary walking speed in the Japanese pre-frail and frail elderly: a randomized controlled trial

Background: To investigate whether continuous intervention using soymilk containing high soy protein improves physical frailty, a randomized controlled trial was conducted among the Japanese pre-frail and frail elderly.

Methods: Japanese pre-frail and frail elderly participants (n = 73) were randomly assigned to the high-soy protein and control groups, who then ingested soymilk containing 14.5 g/200 ml and 3.2 g/200 ml of soy protein, respectively. Before and after the 12-week intervention, walking speed, skeletal muscle mass, grip strength, and the revised Japanese CHS questionnaire regarding fatigue and physical activity were examined to evaluate the impact of each soymilk on physical frailty and compare the variation between the two groups. Physical activity (monitored using a pedometer), dietary intake (determined by questionnaire), and estimated protein intake (determined by casual urine testing) were also recorded before and after the intervention.

Results: For the final analysis of the entire cohort (n = 70), there were no significant differences in the endpoints between the two groups. In the subgroup analysis, among participants with a walking speed of at least 1 m/s (n = 35, P = 0.012) and at least 5,000 steps/day before intervention (n = 27, P = 0.0083), the variation in walking speed after the 12-week intervention was significantly higher in the high-soy protein group than in the control group. Estimated protein intake was also significantly higher in the high-soy protein group than in the control group after the intervention. Regarding physical activity and dietary intake, no significant differences were observed between the groups before or after the intervention.

Conclusion: The continuous 12-week intervention of high soy protein increased the walking speed among the Japanese pre-frail and frail elderly participants who had an ordinarily high walking speed and high step counts.

Trial registration: UMIN Clinical Trials Registry, UMIN000044999. Registered July 29, 2021; https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000051409 .