The Influence of the "washoku" Diet on the Gut Microbiota in Postmenopausal Women

Women who meet the criteria for inclusion in the study for a period of 4 weeks will be randomly assigned to one of two groups: 1. The intervention group will follow the principles of the healthy eating plate, which will be supplemented with elements of the washoku diet (30 g of roasted black soybeans and 5 g of wakame); 2. The control group will be covered only by the principles of the healthy eating plate.

All participants will receive a brochure with information on the recommended portion sizes of individual product groups in the daily diet, recipes for dishes based on roasted black soybeans and wakame. Before and after the study, in addition to anthropometric measurements (body weight, waist circumference, hip circumference), body composition and bone mineral density, an assessment of the diet (using a semi-quantitative questionnaire of food frequency, as well as the current recording method from the last 4 days) and the level of physical activity will be carried out. Additionally, the women will be asked to collect a daily portion of urine to assess the concentration of soy isoflavones and to determine the content of sodium, potassium and magnesium. Women will also have their blood (18 ml) collected to assess selected biochemical parameters (glucose, insulin, total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), non-HDL cholesterol (non-HDL-C) and triglycerides). A stool sample will also be collected to assess the composition of the intestinal microbiota and its metabolites, i.e. short-chain fatty acids. Recruitment will take place via social networking sites, i.e. Facebook.

The following specific analyses were planned:

• Assessment of anthropometric parameters (height, body weight, hips and waist circumference)
• Analysis of body composition and bone mineral density
• Assessment of nutritional status (selected metabolic parameters such as glucose metabolism (glucose, insulin concentration), lipid metabolism (total cholesterol (T-C), LDL cholesterol (LDL-C), HDL cholesterol (HDL-C), non-HDL cholesterol (non-HDL-C) and triglycerides).
• Assessment of dietary habits (a semi-quantitative questionnaire on the frequency of food intake, additionally supplemented by the current recording method from the last 4 days.)
• Assessment of intestinal microbiota composition
• Assessment of fecal short-chain fatty acid concentration
• Assessment of urine soy isoflavones concentration

Normality of the obtained data distribution will be tested using the Shapiro-Wilk test. The Kruskal-Wallis test then will be used for nonnormally distributed data and the Tukey HSD test will be used for normally distributed data. A p value of less than 0.05 was considered statistically. The microbiota composition will be analyzed using RStudio (R version 4.0.3 (2020-10-10)) with packages including phyloseq, microbiome, and vegan. Taxa will be filtered by removing all those not assigned to any phylum. Only taxa with abundances over 0.25% in at least one sample will left in the dataset. All analyses of gut microbiota composition will be performed on the basis of the relative abundances (RA) of the OTUs (Operational Taxonomic Units).

The data collected in the planned studies will include the results of measurements and their statistical analyzes. All data will be collected directly by team members and coded. Detailed instructions on data collection will be prepared by the team leader and each member will need to read and receive appropriate training. All biochemical and anthropometric measurements will be performed in at least two repetitions and will be checked by another team member. All used specialized equipment will be properly calibrated before each use (scale, body composition analyzer, Nanodrop spectrophotometer).

Inclusion criteria

• age 45 to 65,
• at least one year after natural menopause,
• BMI > 25 kg/m2
• waist circumference > 80 cm.

Exclusion criteria

• use of hormone replacement therapy;
• taking antibiotics or probiotics in the last 6 months from the date of commencement of the scientific experiment,
• taking medications regulating carbohydrate or lipid metabolism in the last 4 weeks from the date of commencement of the scientific experiment,
• taking medications regulating body weight in the last 3 months from the date of commencement of the scientific experiment,
• diseases of the thyroid gland, liver, heart, kidneys, digestive system, anemia, neoplastic diseases,
• smoking or alcohol consumption in amounts exceeding 100 g/week.