Dietary Polyphenols and Insulin Sensitivity in Overweight and Obese Humans
Condition: Healthy
MeSH terms: Overweight
Study type: Interventional

Summary: 
      In this double-blind, randomized, placebo-controlled study, we aim to investigate the effects
      of a long-term supplementation on insulin sensitivity, mitochondrial function and substrate
      metabolism in healthy overweight men and women.

      In each group, 21 subjects consume 100mg Resveratrol (RSV) and 150mg Epigallocatechin-gallate
      (EGCG), respectively Placebo capsules, twice daily over a period of 12 weeks. The subjects
      receive the capsules after the last pre-measurement and continue to take them throughout the
      post-measurements.

      Before and after the supplementation period, we perform a hyperinsulinemic-euglycemic clamp
      with a glucose-tracer infusion to assess hepatic and systemic insulin sensitivity.
      Simultaneously, substrate oxidation is measured throughout the clamp by indirect calorimetry.
      Furthermore, we perform a high-fat mixed meal test, in which we collect blood and measure
      substrate oxidation during fasted and postprandial conditions. During the meal tests, extra
      plasma is collected at the start (t=-30) and the end (t=240), of which the supernatant is
      stored in light-protected tubes (EGCG is mixed 1:1 with an EGCG buffer) for analyzing
      polyphenol concentrations in the blood.

      In the male subgroup (21 men), we additionally place each 2 microdialysis probes in the
      subcutaneous adipose tissue and the gastrocnemius in order to assess local lipolysis and
      blood flow by means of ethanol infusion.

      Furthermore, a dexa-scan is performed to assess body composition and biopsies are taken under
      fasted conditions from the subcutaneous adipose tissue and the quadriceps femoralis muscle.
      These samples are stored at -80C. Part of the adipose tissue samples is collected to measure
      adipocyte size. Of the skeletal muscle biopsy, one part is directly buffered and used for the
      oxygraph to measure mitochondrial function.

      At last, feces samples are collected before and after the intervention in order to assess
      energy content, microbial composition and short-chain fatty acid content.

      Based on previous human studies in our and other departments, we hypothesize that after 12
      weeks of the combined polyphenol supplementation, insulin sensitivity and mitochondrial
      function improve. Furthermore, based on results of a short-term study performed by our group,
      that demonstrated an increase in energy expenditure, a positive effect on the regulation of
      body composition might be expected.
    


Intervention name(s): EGCG+RSV-supplementation; Placebo
Intervention type(s): Dietary Supplement; Dietary Supplement
Intervention description(s): Teavigo (~300mg/d) Resveratrol (~80mg/d)
Other intervention name(s): Teavigo, Pure Encapsulations Inc. (Massachusetts, USA); Resveratrol, Pure Encapsulations Inc. (Massachusetts, USA)
Intervention MeSH terms: Resveratrol
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Treatment
Keywords: Polyphenols; Resveratrol; Epigallocatechin-gallate; Insulin sensitivity; mitochondrial function; lipid oxidation; tissue lipolysis