Grape Polyphenols and Second-meal Effect
Condition: Obesity
MeSH terms: Obesity
Study type: Interventional

Summary: 
      The aim of this is study is to evaluate the effects of a single intake of grapes (a
      polyphenol-rich food) in postprandial metabolism in subjects with obesity, including a first
      intake (high-fat breakfast) after overnight fasting a second one (medium-fat lunch). Studies
      on the effects of polyphenols on postprandial (glucidic and lipidic) metabolism have commonly
      been performed in animal models and have used grape extracts, ignoring the whole pool of
      polyphenols present in grapes (extractable and non-extractable polyphenols). Besides, the
      contribution of polyphenols to the so-called second-meal effect has not been explored. It
      should be highlighted that this study aims to explore the potential beneficial role of fresh
      grapes, consumed as fruit; in order to ensure the stability of the product, they will be
      provided as freeze-dried milled material, but the amount received by the subjects could be
      incorporated into a common diet, being equivalent to 300 g of fresh grapes.
    

Detailed description: 
      Twenty-five subjects with obesity will be were recruited. Detailed inclusion and exclusion
      criteria are provided below.

      The subjects will receive, after overnight fasting, either a monodose of freeze-dried grapes
      (equivalent to 300 g of fresh grapes) or isocaloric placebo solved in water, together with a
      high-fat breakfast. Blood samples will be collected before the intake, up to 5 h after
      breakfast, then a medium-fat lunch will be provided and blood samples will be collected for
      three additional hours. Both interventions will be separated by two weeks. The following
      determinations will be performed in blood samples collected at different periods: glucose,
      insulin, triglycerides, uric acid, viscosity, antioxidant capacity. Additionally, a satiety
      test will be provided. It is expected that grape supplementation, as compared with an
      isocaloric placebo, causes significant modifications in all the parameters indicated.
      Nevertheless, the primary outcome of this study is the area under the curve for glucose after
      the second meal (300-420 min from basal time).
    

Intervention name(s): Freeze-dried grape (GRAP)/Placebo (PLA)
Intervention type(s): Other
Intervention description(s): The subjects will receive, after overnight fasting, either a monodose of freeze-dried grapes (equivalent to 300 g of fresh grapes) or isocaloric placebo solved in water, together with a high-fat breakfast. Blood samples will be collected before the intake, up to 5 h after breakfast, then a medium-fat lunch will be provided and blood samples will be collected for three additional hours. A total of 10 samples will be collected: 0-30-60-120-180-240-300-330-360-420 min. Both interventions will be separated by two weeks. Subjects will be instructed not to modify their dietary habits during the development of the study, but during the 72 h before each visit they will have to restrict the intake of polyphenol-rich foods (a detailed list will be provided).
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: GRAP: dried and milled grape pomaces. PLA: control period. All the subjects will pass the two periods: one half will receive the acute PLA supplementation followed by the acute GRAP supplementation, and the other half will do it inversely. The assignment to each order will be done randomly. Both period will be separated by a two weeks washing period.
Masking: Double (Participant, Care Provider)
Primary purpose: Basic Science
Keywords: Polyphenols; Obesity; Grape; Postprandial; Insulin resistance; Second meal effect