This study aims to investigate the effects of RT-90 resistant cassava starch on glycemic control using a human dietary trial and to evaluate its potential as a prebiotic fiber supplement. This study will assess the efficacy of RT-90 resistant cassava starch in improving glycemic control, body composition, and gut microbiome in healthy individuals.

This study consisted of two phases.

The first phase was conducted in a randomized, cross-controlled manner. Before entering the study, participants maintained a normal diet and lifestyle for three consecutive days. Afterward, they entered the study and underwent a resistant starch assessment until the end of the study. Forty participants were randomly divided into two groups: 20 in each of the Weidan resistant starch group and the glucose powder group. Weidan resistant starch consists of tapioca resistant starch and glucose powder. Both groups consumed the sample within 5 minutes and then underwent an oral glucose tolerance test (OGTT). The participants fasted for 8-12 hours the day before the test (water was permitted). Blood samples (1 mL each) were collected at 0, 30, 60, 90, 120, and 180 minutes to monitor blood glucose levels. After the study, the two groups consumed either Weidan resistant starch or 50 g of glucose powder, each containing 50 g of total carbohydrates (57 g total product weight), dissolved in 250 mL of water, within 5 minutes, at least one week after the study. Blood glucose levels were monitored. After the study, the two groups alternated and consumed Weidan resistant starch or glucose powder again, followed by an oral glucose tolerance test and body composition measurements using the Inbody270 body composition analyzer.

The second phase of the study was conducted in a randomized, double-blind, placebo-controlled manner. Prior to entering the study, participants maintained a normal diet and lifestyle for three consecutive days. Afterward, they entered the study and underwent resistant starch assessment until completion. 75 subjects were randomly divided into three groups: the Weidan resistant starch group, the commercial resistant starch group, and the placebo control group. The ingredients of Weidan resistant starch are cassava resistant starch; the ingredients of commercial resistant starch are wheat resistant starch; and the placebo control group are natural cassava starch. The dosage is calculated based on 0.5 grams per kilogram of adult body weight (for example, a 60-kilogram adult needs to take 30 grams). The subjects were required to dissolve the test product in water and drink it on an empty stomach before their first meal each day for 12 weeks. The evaluation items at each follow-up visit included: (1) general physical examination (mental state, sleep, appetite, gastrointestinal symptoms, blood pressure, pulse and respiratory rate), (2) body measurement and body composition analysis (weight, BMI, waist circumference, hip circumference, subcutaneous fat thickness, skeletal muscle weight, body fat percentage and total water weight), (3) routine blood and biochemical examination, including red blood cell and white blood cell count, hemoglobin, hematocrit, mean corpuscular volume and platelets, renal function (urea nitrogen, creatinine, uric acid), thyroid hormone, liver function (AST, ALT, γ-GT and albumin), blood lipids (triglycerides, total cholesterol, free fatty acids, high-density lipoprotein cholesterol and low-density lipoprotein cholesterol), electrolyte balance (sodium, potassium, chloride, phosphorus, calcium) and fasting blood glucose (blood volume was 15 mL, must fast for at least 8 hours), (4) diet and activity records (including 24-hour diet review and weekly gastrointestinal function symptom records), (5) analysis of intestinal related indicators, including short-chain fatty acids (SCFA) and intestinal flora (NGS). Samples were collected and analyzed at week 0 and week 12.

Inclusion Criteria:

• Subjects aged 18-65 years.
• Healthy subjects (BMI between 18.5-24.9 kg/m² for women and men).
• Subjects must be able to maintain a stable diet (based on the Ministry of Health and Welfare's daily dietary guidelines, with a tolerance of ± 10-15%) and physical activity (based on the World Health Organization's recommendations of 150-300 minutes of moderate-intensity exercise per week, or equivalent physical activity, with a tolerance of ± 20%) during the trial period.
• Subjects must understand the trial procedures and potential risks and benefits described in the consent form and be able to sign the consent form.

Exclusion Criteria:

• Pregnant or breastfeeding women.
• Subjects with endocrine abnormalities, major organ disease, or mental illness (as determined by a physician).
• Subjects found to be intolerant to the test sample during the trial.
• Subjects who develop a disease or take medications or health supplements that could affect the results of the trial during the trial period. (e.g., hypoglycemic (lipid)-lowering medications, probiotics, high-dose dietary fiber supplements, fish oil, or supplements high in polyunsaturated fatty acids).
• Chronic gastrointestinal diseases (e.g., diverticular disease, irritable bowel syndrome, or other intestinal diseases that may cause constipation).
• Use of antibiotics within the past three months.