Subjects In this trial, 8 healthy subjects (6 women and 2 men), aged between 23-37 years old were voluntarily recruited. Inclusion criteria were: healthy men or women aged between 18-50 years old, body mass index (BMI) between 18.5-25.0, normal diet, not under any medication, and not having any history of metabolic diseases or abnormalities such as systemic hypertension (resting blood pressure more than 140/90 mmHg), impaired glucose tolerance (fasting blood glucose concentration between 100-126 mg/dL and oral glucose tolerance test or OGTT more than 140 mg/dL), and non-alcoholic fatty liver diseases (NAFLD). Subjects were excluded if they had an acute infection, pregnant, gastrointestinal disease, cardiovascular disease, renal disease, pancreatic disease, and take any medication during or 1 week before trial. At the beginning of the trial, demographic data including age, sex, history of diseases, medication, diet, and physical activities within 3 days were collected using a questionnaire form. Bodyweight was measured using Omron digital scale HN286 (PT. Omron Manufacturing of Indonesia). Body height was measured using a stature meter. To determine the amount of daily calorie expenditure for selection of the suitable ready-meal, the estimated energy requirements (EER) were calculated based on the harris-benedict formula as previously reported45, with the physical activity level 1.0 (sedentary activity). This research was approved by the Health Research Ethics Committee of Widya Mandala Catholic University Surabaya (No. 131/WM12/KEPK/DOSEN/T/2020).

Experimental design This experimental design adapted a single-arm trial analysis. A group of 8 subjects received intervention with single pre-meal supplementation. After that, the glycaemic response was measured (see blood sampling preparation). This intervention was repeated every week with five different supplementation formulae (see below) for five consecutive weeks. The difference in their glycaemic response after meal for every intervention was measured and analyzed statistically.

Supplement preparation: Inulin formulations, isomaltooligosaccharides formulations, the combination of inulin and isomaltooligosaccharides formulations, dextrose solution, and vehicle-glucose formulations.

For the first week, the investigators measured glycaemic response to a meal without any intervention and use those data as a baseline. For the intervention, the investigators used the untreated control without supplementation (NS), HP Inulin formulations (IF), isomaltooligosaccharides/IMO formulations (IM, this formulation is marketed as Fibercreme®), the combination of HP inulin and IMO formula (MF), dextrose solution (DS), and vehicle-glucose formulations (VO) in the form of powder. All the supplementation formulas are purchased from PT. Lautan Natural Krimerindo (Mojokerto, Jawa Timur, Indonesia). The detailed composition of each formulation could be seen in Supplementary Table 1. For the preparation of 20% IF, IM, and MF solution, 20 grams of designated powder was diluted in 100 ml distilled water. For 20% DS, 20 grams of purified dextrose monohydrate was diluted in 100 ml distilled water. IMO solution was chosen as a control because IMO could act as partially digestible dietary fibre.43 Vehicle-glucose could act as a negative control for IF intervention because IF contains similar ingredients with the IF, but instead of inulin, glucose syrup was added as the caloric source.

Intervention: fasting, pre-meal supplementation, and meal Three days before the intervention, every subject was informed to maintain their normal diet, physical activities, and enough sleep (6-8 hours/day). All subjects fasted 10-12 hours before the intervention. Supplement formula solution 20% (w/v) then given orally before a meal for five consecutive weeks in the following orders: IF in the first week, followed by IM in the second week, MF in the third week, DS in the fourth week, and VO in the last week. The meal for experimental subjects was given after intervention and contained 470 kcal "Ready Meal". The amount of calories in "Ready-Meal" is 25-30% from the calculated EER (see table 1). The macronutrient composition of the "Ready Meal" was purchased from PT. Charoen Pokphand Indonesia,TbK (Jakarta, Indonesia) was listed in supplementary table 2.

Blood sampling preparation, blood glucose, and glycaemic response (iAUC) measurement.

An intravenous cannula was inserted into the cubital vein to provide access to repeated glucose measurement. Peripheral vein whole blood samples were taken for analysis of glucose concentration using a commercially available FreeStyle Optium glucose monitoring system (Abbot Laboratories, Chicago, Illinois, USA). Blood glucose was measured at 0, 30, 60, 90, and 120 minutes after intervention and meal. The first measurement at 0 representing the fasting plasma glucose (FPG), that is the blood glucose concentration after an overnight fast (10-12 hours). The glycaemic response measurement unit at 0, 30, 60, 90, and 120 minutes for each subject was described as the incremental area under the curve (iAUC). The iAUC refers to actual body exposure to certain substances after their administration. The AUC depends on the rate of substance elimination from the body and its dose of administration. iAUC calculation (symbolized with A) was carried out using a linear trapezoidal method and formula (see supplementary figure 1) as described in the literature.44