Dietary Carbohydrate and Internal Body Fat

Visceral fat mass (cm3) measured by computed tomography (CT) imaging

Circulating insulin concentrations measured before and 2 hours after intake of a standardized mixed meal

Circulating C-peptide concentrations measured before and 2 hours after intake of a standardized mixed meal

Triacylglycerol concentrations measured before and 4 hours after intake of a mixed meal

Circulating glucose measured before and after 30, 60, 90, 120 and 240 minutes after intake of a standardized mixed meal

Circulating non-esterified fatty acid concentrations before and after 60, 120 and 240 minutes after intake of a standardized mixed meal

Microbiome composition measured by 16S sequencing

Calculated as liver/spleen attenuation index (Hounsfield units) based on quantification by computed tomography (CT) imaging

Pericardial fat mass (cm3) measured by computed tomography (CT) imaging

Abdominal subcutaneous fat mass (cm3) measured by computed tomography (CT) imaging

CAC score calculated based on computed tomography (CT) imaging

Waist circumference (cm) measured by a measuring tape

Body-mass index measured as body weight (kg) divided by height (m) squared

Circulating fasting insulin concentrations

Circulating fasting C-peptide concentrations

Circulating fasting triacylglycerol concentrations

Circulating fasting high-density lipoprotein cholesterol (HDL-C)

The ratio of circulating fasting triacylglycerol (TAG) and high-density lipoprotein cholesterol (HDL-C)

Circulating fasting low-density lipoprotein cholesterol (LDL-C)

Circulating fasting apolipoprotein profile measured by multiplex ELISA

Circulating metabolites in the serine, glycine and histidine pathways measured in the fasted state by GC-MS/MS

Total fat mass measured by bioimpedance analysis (BIA)

Lean mass will be measured by bioimpedance analysis (BIA)

Subjective appetite and fullness assessed and quantified by the VAS questionnaire

Gastrointestinal health will be surveyed and quantified by a questionnaire (Rome III Diagnostic Criteria for Irritable Bowel Syndrome (IBS)). The questionnaire surveys criteria for diagnosis of IBS within a 12-week period. The criteria for IBS are based on recurrent abdominal pain or discomfort, 3 days per month in the last 3 months (12 weeks), associated with ≥2 of the following criteria: 1.Improvement with defecation; 2. Onset associated with a change in stool frequency; 3. Onset associated with a change in stool form (appearance). The criteria are fulfilled with symptoms onset 6 months prior to diagnosis.

Gastrointestinal health will be surveyed by the IBS-SSS questionnaire. Scores on the IBS-SSS range from 0 to 500 with higher scores indicating more severe symptoms. Subjects can be categorized as having mild (75-175), moderate (175-300), or severe (>300) IBS. A decrease of 50 points is associated with a clinically meaningful improvement. Each question on the VAS ranges from 0-100mm, where higher score indicates more severe symptoms.

The categorization based on scores (total possible score = 500) are as follows:

0-75 = not IBS 75-175= mild IBS 175-300 = moderate IBS 300-500 = severe IBS

The Fatigue Impact Scale will be used to compute a total score for fatigue by summing up the scores for subclasses as follows: cognitive functioning (10 items, subscale range: 0-40), physical functioning (10 items, subscale range: 0-40), and psychosocial functioning (20 items, subscale range: 0-80). The statements are ranged on a five-level scale (0 = no problem to 4 = extreme problems), giving a maximum total FIS score of 160 (total scale range: 0-160) where low scores indicate less fatigue-related issues.

Obesity-specific quality of life is measured with "Patient-Reported Outcomes in Obesity" (PROS), which consists of 8 items tapping how different life domains are affected by obesity. PROS have one overall score, ranging from 0 (optimal) to 3 (poorest).

Generic health-related quality of life is measured with RAND-36, which consists of dimensions ranging from 0 (poorest) to 100 (optimal). There are 8 subscales; physical functioning, physical role functioning, bodily pain, general health, vitality, social functioning, emotional role functioning and mental health. In addition, RAND-36 also have 2 summary scores: the physical component summary (PCS) (tapping from physical functioning, physical role functioning, bodily pain and general health) and mental component summary (MCS) (tapping from vitality, social functioning, emotional role functioning and mental health).

The SF-NDI (Short-Form Nepean Dyspepsia Index (SF-NDI)) questionnaire will be used to assess quality of life / psychological wellbeing related to gastrointestinal symptoms. The 10-item SF-NDI was constructed and validated in patients with functional gastrointestinal disorders for measuring health-related quality of life. The 10-item short form includes five subscales: tension, interference with daily activities, eating/drinking, knowledge/control, and work/study, and each subscale contains two items. The items were measured by a 5-point graded Likert scale from 1 to 5. A total sum score for quality of life and a sum score for each of the five subscales were calculated by adding up scores for each item (range of total quality of life, 10-50; range of each subscale, 2-10). Higher scores indicate worse functioning or symptoms.