The Role of Traditional or Western Diet in the TBC1D4 Gene on Glucose Homeostasis in Greenland Inuits
Condition: T2D
Study type: Interventional

Summary: 
      Studies of Greenland Inuit before the 1980s found a low prevalence of type 2 diabetes (T2D)
      compared to Western populations. However, recent population studies in Greenland found a
      notably high prevalence of diabetes (9%) and pre-diabetes (19%) in the adult population.

      In many studies worldwide an increase in obesity, diabetes, and cardiovascular disease has
      been ascribed to social transition and in particular urbanization, but the Inuit in Greenland
      do not fit the pattern. Paradoxically, the highest prevalence of diabetes is seen in the
      least urbanized areas. Thus, while previously rare, T2D has become epidemic in Inuit. In a
      recent study by Moltke et al found that a variant in the TBC1D4 gene was strongly associated
      with insulin resistance in skeletal muscle, high postprandial blood glucose and a high risk
      of T2D.

      The rapid increase in the prevalence of T2D and other metabolic traits and the well
      documented genetic susceptibility indicates that lifestyle components, particularly physical
      activity, and diet significantly modify the genetic effects on glucose homeostasis. Thus,
      changing dietary habits from a diet high in traditional foods, mostly consisting of marine
      mammals and fish (high in protein and unsaturated fats, and low in carbohydrate) to a
      westernized diet, with high contents of sugar and saturated fat may have increased the T2D
      incidence in Arctic Inuit.

      The investigators will perform a 4-week cross-over intervention study of the traditional diet
      versus a western diet among homozygous carriers and WTs on 2-hour glucose after an oral
      glucose tolerance test (OGTT). In addition, the investigators will examine the effects on
      cardiometabolic abnormalities such as low-grade systemic inflammation and dyslipidemia.
      Furthermore, the investigators will characterize the metabolic phenotype of participants, as
      well as gut microbiota and brown adipose tissue markers to elucidate the molecular mechanisms
      underlying potential improvements of a traditional Inuit diet.
    

Detailed description: 
      The overall objective of the study is to investigate whether a traditional marine diet high
      in fat and low in carbohydrate compared to a westernized diet could improve glycemic control
      in Greenland Inuit. Furthermore, the objective is to study whether the genetic risk of
      postprandial hyperglycemia among Greenlandic carriers of the common nonsense p.Arg684Ter
      variant in the TBC1D4 gene is modified to a larger degree by the diet compared to
      non-carriers.

      The investigators will perform a 4-week cross-over intervention study of the traditional diet
      versus a western diet among homozygous carriers and WTs on 2-hour glucose after an oral
      glucose tolerance test (OGTT). In addition, the investigators will examine the effects on
      cardiometabolic abnormalities such as low-grade systemic inflammation and dyslipidemia.
      Furthermore, the investigators will characterize the metabolic phenotype of participants, as
      well as gut microbiota and brown adipose tissue markers to elucidate the molecular mechanisms
      underlying potential improvements of a traditional Inuit diet.

      The study is expected to provide relevant information in relation to whether diet has a role
      in preventing T2D in the large group of people who are hetero / homozygous for the TBC1D4
      variant. The investigators expect this enhanced insight to be useful and valuable for future
      development of genotype based interventions for these persons.

      For the individual participant, the results of the study are expected to provide constructive
      knowledge to guide the participants in which actions they could take to reduce the likelihood
      of developing T2D.

      Hypothesis

      The investigators hypothesize that the traditional marine diet very high in fat and low in
      carbohydrates will improve postprandial glucose handling in Greenland Inuit. Furthermore, the
      investigators hypothesise that this effect is modified among carriers of the common nonsense
      p.Arg684Ter variant in the TBC1D4 gene which will have larger effects of following the
      traditional marine diet.

      Methodology

      Overall study design 30 homozygous carriers and 30 homozygous non-carriers of the nonsense
      p.Arg684Ter variant in the TBC1D4 gene between 18-80 years will be included in the study.

      The study will be conducted as a randomized, controlled, cross-over design, comprising two
      dietary intervention periods of four weeks duration, with no washout in between. The
      participants will be randomized to start on one of the two diet periods and cross-over to the
      other dietary period at 4 weeks (see figure 1). The investigators expect to recruit
      participants after approval from April 2019 and have the last patient last visit by September
      2020. Recruitment of study participants will be based on the currently ongoing Greenland
      Population Study (project 2017-5582) to ensure that the investigators have 50% homozygous
      carriers of the nonsense p.Arg684Ter variant in the TBC1D4 gene. The study will be carried
      out in three geographical areas: Nuuk, Qaanaaq, and Qasigiannguit.

      Randomization, allocation, concealment, and blinding

      After having given oral and written consent, randomization will be performed separately for
      each participant based on the genotype in blocks of variable size to ensure equal
      randomization throughout the enrolment phase of the study. The randomization sequence will be
      done by an investigator without contact to the participants. The personnel conducting the
      study will allocate participants to the sequence of intervention using a list of participant
      IDs matched with allocated sequences. Blinding participants is not feasible due to the nature
      of the intervention, however blinding of the allocation sequence will be established during
      sample analysis and initial data analysis.

      Intervention

      Two diets will be designed for the intervention. A traditional Inuit diet (TID) rich in
      marine mammals (such as walrus, seal, and whale), fish, caribou and musk ox, with low intake
      of grains, fast food, and other imported foods. The TID diet will be high in fat (>40 of the
      energy (E%)) and low in carbohydrate (<30 E%). The Westernized diet will be consisting of
      high amounts of grains, potatoes, rice and imported meats from livestock animals (beef, pork,
      and chicken). The Westernized diet will be high in carbohydrate (55-65 E%) and lower in fat
      (30-35 E%). Major parts (20-25E%) of the diet will be given to the participants upon start
      and during the study in the form of frozen goods. For the TID group, this will be marine
      mammals and fish, while for the Westernized group the products delivered will mainly be
      grains and livestock animals. Instructions for the participants regarding the incorporation
      of dietary changes will be performed by trained study staff.

      Study products

      Assessment of habitual food intake at baseline will be conducted with a previously validated
      food frequency questionnaire. A modified version of the food frequency questionnaire will be
      used at the end of each intervention period for assessing habitual diet during the
      intervention period. In addition, participants will be asked to keep a simple log of
      ingestion of delivered products to estimate compliance. The investigators will apply for
      sponsorship for study products. The potential study product sponsors will play no role in the
      design, methods, data management and analysis or in the decision to publish.

      Consumption of Study products

      Trained study personnel will provide participants with instructions on how to incorporate the
      provided study products in the diet. Initially, it will be ensured that the study products
      are provided in sufficient amounts to ensure ad libitum consumption. Participants will be
      provided individualized amounts of all study products every second week. All study products
      are provided as fresh or frozen products, and all food products will be picked up at the
      local study site.

      Study examinations

      Participants will arrive for clinical examination after an overnight fast of at least 8
      hours. Lifestyle questionnaires, including a food frequency questionnaire and questionnaires
      about medication use, will be performed for baseline characterization of the participants.
      Blood pressure and anthropometric measurements are performed including measurements of body
      weight, height, waist and hip circumference, sagittal abdominal diameter and bio-impedance
      measurements for assessing body fat mass. A fasting blood sample is obtained and an OGTT is
      performed with collection of blood samples after 0, 30 and 120 min. Samples will be analyzed
      with standard clinical procedures for glycaemic variability markers, including glucose,
      insulin, c-peptide, and HbA1c, as well as plasma lipids. Circulating fatty acids profiles
      will be used as a marker of compliance with the TID using dried blood spots. Furthermore,
      fecal samples will be collected at all examination visits and kept stored for future
      microbiota analyses, using untargeted shotgun sequencing. Biobanked samples will be stored
      for further analyses which could include gastrointestinal hormones, gut microbiota
      metabolites, additional compliance markers such as alkylresorcinols (for grain intake)
      low-grade inflammation markers and markers of brown fat accumulation. In addition,
      participants will be equipped with a 24-h continuous glucose monitoring device for 14 days at
      the end of each intervention period. All 3 examination days consists of similar examinations
      and data collections and are estimated to last approximately 5 hours.
    

Intervention name(s): Cross-over study
Intervention type(s): Other
Intervention description(s): Traditional Inuit Diet vs Westernized Diet
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Single (Investigator)
Primary purpose: Prevention
Keywords: Greenland Inuit; Traditional diet; TBC1D4