Soy protein soymilk and muscle mass in older Japanese adults
What it found
In a 12-week trial in older Japanese adults, high-soy-protein soymilk did not change muscle mass across all participants.
In a subgroup of pre-frail participants, those who drank it showed a small increase in muscle mass compared with the control group.
What they found
Studies in people
Muscle mass overall
Across all 68 participants, the change in skeletal muscle index did not differ significantly between the high-soy-protein group and the control group.
Pre-frail subgroup
Among the 58 pre-frail participants, those in the high-soy-protein group had a small but significantly greater increase in skeletal muscle index than those in the control group.
Active subgroups
In pre-frail participants who walked 5000 or more steps a day, or who burned 30 or more kcal per kg body weight per day, the high-soy-protein group showed a significantly greater increase in skeletal muscle index.
Energy intake subgroup
In pre-frail participants who ate 30 or more kcal per kg body weight per day, the high-soy-protein group had a significantly greater increase in skeletal muscle index.
Male subgroup
Among pre-frail men, the high-soy-protein group showed a significantly greater increase in skeletal muscle index than the control group. The authors note there were few women in this analysis.
What the authors conclude
“In this study, no significant improvement in the SMI was observed across all subjects (frail and pre-frail elderly individuals); however, an exploratory subgroup analysis suggested that continued daily HSP soymilk intake was associated with potential benefits in pre-frail elderly individuals with high physical activity and energy intake levels.”
Also in their conclusions
- They conclude that no significant improvement in skeletal muscle index was seen across all subjects.
- They say that an exploratory subgroup analysis suggested continued daily high-soy-protein soymilk intake was associated with potential benefits in pre-frail elderly individuals with high physical activity and energy intake levels.
- They state that these findings are preliminary and require further research.
How it was done
The authors wanted to see whether daily high-soy-protein soymilk could help maintain or increase skeletal muscle mass in frail and pre-frail older people, since muscle loss is a key part of frailty.
They studied 68 Japanese adults aged 65 to 83 who were frail or pre-frail. For 12 weeks, one group drank soymilk with 14.5 g of soy protein per 200 mL, and the other group drank soymilk with 3.2 g of soy protein per 200 mL. Muscle mass was measured before and after.
What it can’t tell you
- The subgroup findings are exploratory and come from analyses done after the study ended, so they need confirmation in future studies.
- The study lasted only 12 weeks, so it cannot show what happens over a longer period.
- The participants were a small, similar group of Japanese older adults, so the results may not apply to other populations.
Who paid
- Funding
- Funded by MARUSAN-AI Co., LTD. (from the PubMed record).
- Conflicts
- D.S., Y.T., M.S. and R.U. are employees of MARUSAN-AI Co., Ltd. T.U. received an honorarium from Healthcare Systems Co., Ltd., the research contractor. The sponsor had no role in the design of the study; in the collection, analysis, or interpretation of data; in the writing of the manuscript; or in the decision to submit the article for publication.
- Authors work at
- Aichi Gakuin University, Japan; Research Institute, Japan; Nagoya University Graduate School of Medicine, Japan
The paper
- Title
- The Effect of Routine High-Soy-Protein Soymilk Intake on the Skeletal Muscle Index (SMI) in Japanese Pre-Frail Elderly Individuals with an Ordinary Life: A Post Hoc Analysis of a Randomized Controlled Trial
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Sakamoto D, Terashima Y, Sugawara M, et al (2025). The Effect of Routine High-Soy-Protein Soymilk Intake on the Skeletal Muscle Index (SMI) in Japanese Pre-Frail Elderly Individuals with an Ordinary Life: A Post Hoc Analysis of a Randomized Controlled Trial. Nutrients. doi:10.3390/nu17243900Free full textPubMed 41470845DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error