Soy protein intake has also shown to increase the amount of bacteria that produce short-chain fatty acids. These bacteria include Roseburia faecis and Agathobaculum butyriciproducens.
Writing in the Journal of Cachexia, Sarcopenia and Muscle, the researchers from Wilmar (Shanghai) Biotechnology Research & Development Center and institutions like Shanghai Elderly Nutrition and Health Quality Control Center, said that soy protein–rich dietary intervention may reduce the presence of pathogenic bacteria, attenuate inflammatory responses and enhance gut and muscle health.
A total of 84 seniors aged 60 and above took part in the 12-week clinical trial, where they were randomized to take soy protein-rich diets or stick to their usual diet.
The intervention group, for instance, consumed three meals a day supplemented with 30 grams of soy protein, equivalent to 10 grams per meal.
Two types of soy protein were consumed by the participants, namely, textured soybean protein and soy protein powder. The soybean tissue protein was added to various Chinese dishes, whereas the soy protein powder was added to soup, congee, beverages and oatmeal.
The participants’ calf circumference, skeletal muscle index, handgrip strength and blood biomarkers like interleukin-6 (IL-6), insulin growth factor (IGF-1), high-sensitivity C-reactive protein (hs-CRP) and 25-hydroxyvitamin D were measured to assess the effect of soy protein-rich diets.
The researchers also took faecal samples from the participants at baseline and follow-up to assess the changes in their gut microbiome.
Improvements in calf circumference, walking test
Findings showed that a soy protein-rich diet could maintain muscle health, specifically calf circumference and improvements in the 6-meter walk test, as compared to the control group.
Calf circumference, for instance, had decreased for the control group, but was preserved in the intervention group, and the difference between the two groups was statistically significant.
Similarly, the intervention group’s 6-meter walk test showed a reduction in the time required to complete the distance, while the control group showed an increase from baseline, with the difference in timing approaching statistical significance, where p=0.05.
However, both groups showed similar temporal patterns in Short Physical Performance Battery (SPPB), handgrip strength (HGS) and five-time chair stand test performance across the study period.
Gut microbiome changes
Further analysis showed significant gut microbiome changes in individuals with improved calf circumference in the intervention group.
Specifically, they have shown an increase in short-chain fatty acid-producing bacteria, such as Roseburia faecis and Agathobaculum butyriciproducens.
At the same time, they showed a decrease in bacteria species associated with poorer muscle outcomes, such as Alistipes putredinis and Eubacterium_sp_CAG_38.
These findings also support existing knowledge of microbial diversity and sarcopenia.
The researchers cited a paper published in Scientific Reports in 2021, which reported that butyrate producers such as Lachnospira, Fusicantenibacter, Roseburia, Eubacterium and Lachnoclostridium were significantly less abundant in sarcopenia and possible sarcopenia individuals, while Lactobacillus was more abundant.
The current study also showed that butyric acid, isobutyric acid and isovaleric acid were the short-chain fatty acids that had increased among individuals with improved calf circumference and 6-m walk test results.
For instance, at the midpoint of the study, the amount of butyric acid was up 0.74 ± 0.34 mg/g from baseline, which was a significant increase. A slight increase in butyric acid of 0.12 ± 0.43 mg/g was also observed in the control group, but the increase was not statistically significant.
Biomarkers analysis
There was a significant decrease in the inflammatory marker interleukin-6 (IL-6) in the intervention group, while that of the control group remained unchanged.
However, there were no significant changes in the other biomarkers, such as hs-CRP and IGF-1, in either groups.
Both groups also exhibited significant reductions in 25-OH Vitamin D levels.
“These findings indicate that our soy protein–rich dietary intervention may have the potential to reduce the presence of pathogenic bacteria, attenuate inflammatory responses and enhance gut and muscle health," the researchers wrote.
They concluded that although a causal relationship could not be determined, the findings had nonetheless supported the gut–muscle axis hypothesis.
“Although causality cannot be established within the scope of our metagenomic analysis, these findings suggest plausible mechanisms through which the gut microbiome may interact with host muscle physiology and highlight potential targets for future mechanistic studies.”
Source: Journal of Cachexia, Sarcopenia and Muscle. doi: 10.1002/jcsm.70212. "The Effects of Soy Protein–Rich Meals on Muscle Health of Older Adults Are Linked to Gut Microbiome Modifications.“ Authors: X. Wu,K. J. Lim,Y. Ma, et al.
