Dietary Carbohydrate and Internal Body Fat (CARBFUNC)

This is a 2-year randomized controlled trial to test the effect of dietary carbohydrates, both quality and quantity, on changes in internal body fat mass. Up to 250 women and men with obesity are recruited in Bergen, Norway, and randomized to one of the following normo- and isocaloric dietary patterns (same amount of protein, polyunsaturated fatty acids and moderate energy, 2,000 - 2,500 kcal per day): 1) a low-fat high-carbohydrate diet primarily with refined (e.g., flour-based) carbohydrate sources, 2) a low-fat high-carbohydrate diet based on minimally refined (e.g., cellular) carbohydrate sources, and 3) a very-high-fat low-carbohydrate diet.

Obesity, and high internal fat storage in particular, represents a tremendous and increasing health challenge across the world, and is linked to the recent introduction and globalization of an ultra-processed food supply largely based on refined carbohydrates. However, more high-quality studies are needed to directly assess the role of carbohydrate quality in abdominal adiposity. We also need studies with greater long-term adherence to prescribed food profiles, which may be achievied with the help of new electronic tools such as meal planning applications. The participants select and plan all meals among a list of carefully designed options, using an application/recipe booklet developed for the study. Each recipe/meal/snack is designed to fully comply with the overall macronutrient- and dietary profile for the respective groups. We will further instruct the participants to record their meal choices during three days every 14 days, and to record all deviations throughout the intervention. Enrolled participants are invited to study visits at baseline and after 3, 6, 9, 12 and 24 months. At all or some of these time points, the participants provide biological samples (blood, urine and feces, and for some, adipose and/or muscle tissue) and undergo phenotyping, e.g., measurement of body weight and fat mass by bioelectrical impedance analysis and low-radiation CT imaging, and a standardized meal test with blood sample collection up to 4 hours postprandially. In addition, participants will be asked to fill out a collection of questionnaires that assess quality of life, motivation, fatigue, gastrointestinal health, appetite and physical activity. We ask the participants to maintain the same level of physical activity throughout the study. The primary outcome measure is change in internal body fat mass (visceral adipose tissue) measured by CT imaging. Secondary outcome measures include change in 2-hour postprandial serum concentrations of insulin, change in 4-hour postprandial serum concentrations of triacylglycerols, and change in fecal microbiota composition measured by 16S sequencing.

Prescribed dietary pattern. Carbohydrates from acellular sources, e.g., refined flour/bakery products, at least 500 grams of fruits/vegetables per day, and a macronutrient composition within typical nutritional recommendations for the general population.

Prescribed dietary pattern. Carbohydrates from cellular sources, e.g., root vegetables, fruits, whole-grain rice, non-flour grain products, at least 500 grams of fruits/vegetables per day, and a macronutrient composition within typical nutritional recommendations for the general population similar to the acellular carbohydrate diet.

Prescribed dietary pattern. Energy largely from fat, cellular carbohydrate sources, and otherwise similar food types as in the acellular/cellular carbohydrate diets including at least 500 grams of fruits/vegetables per day.

Participants will be asked to consume 2,000 - 2,500 kcals, thereof 45 energy percent (E%) carbohydrate (up to 5 E% added sugar), 30 E% fat (10-12 E% saturated fatty acids and 7-10 E% polyunsaturated fatty acids) and 17 E% protein. They will use an original online/smartphone application that provides choices of meals/food combinations/recipes corresponding to their prescribed macronutrient profile and dietary pattern. Participants are asked to complete 3-day dietary records every 14 days throughout the study, and to report any deviations from the planned interventions.

Participants will be asked to consume 2,000 - 2,500 kcals, thereof 45 energy percent (E%) carbohydrate (up to 1 E% added sugar), 38 E% fat (10-12 E% saturated fatty acids and 7-10 E% polyunsaturated fatty acids) and 17 E% protein. They will use an original online/smartphone application that provides choices of meals/food combinations/recipes corresponding to their prescribed macronutrient profile and dietary pattern. Participants are asked to complete 3-day dietary records every 14 days throughout the study, and to report any deviations from the planned interventions.

Participants will be asked to consume 2,000 - 2,500 kcals, thereof 10 energy percent (E%) carbohydrate (up to 1 E% added sugar), 73 E% fat (30 E% saturated fatty acids and 7-10 E% polyunsaturated fatty acids) and 17 E% protein. They will use an original online/smartphone application that provides choices of meals/food combinations/recipes corresponding to their prescribed macronutrient profile and dietary pattern. Participants are asked to complete 3-day dietary records every 14 days throughout the study, and to report any deviations from the planned interventions.

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

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

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

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

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

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.

Inclusion Criteria: Body-mass index (BMI) equal to or above 30 kg/m2 and/or waist circumference equal to or above 102 cm for men and 88 cm for women Weight stable during the last 2 months before start of the study (less than 5 % change in body weight up or down) No known diabetes or consumption of diabetes medication Desire to follow a specified dietary pattern using specific recipes throughout the time of the study period Ability to periodically record food intake using a specially designed app for the study Exclusion Criteria: Use of statins and/or diabetes medication Recent surgical or antibiotics treatment during the last 2 months before start of the study Chronic inflammatory bowel disease Serious disease Smoking Pregnancy or breast feeding Alcohol consumption during the study of more than 2 alcohol units per day (1 unit = 15 ml (12.8 g) pure alcohol)

Forskningsenhet for helseundersøkelser (research unit for clinical trials), Department of Clinical Science, University of Bergen

Sommersten CH, Laupsa-Borge J, Andersen AIO, Fasmer KE, Holmefjord MA, Revheim I, Johannessen KK, Naesheim NT, Storas I, Leikanger T, Amundsen K, Skjerve KL, Lawrence-Archer L, Spjelkavik C, Haldorsen I, Lindseth I, Dierkes J, Mellgren G, Dankel SN. Diets differing in carbohydrate cellularity and amount similarly reduced visceral fat in people with obesity - a randomized controlled trial (CARBFUNC). Clin Nutr. 2022 Oct;41(10):2345-2355. doi: 10.1016/j.clnu.2022.08.028. Epub 2022 Sep 5.