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.
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).
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
DOUBLE
Enrollment
25
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).
Institute of Food Science, Technology and Nutrition, National Research Council (ICTAN-CSIC)
Madrid, Spain
Postprandial glucose (300-420 min)
Changes of postprandial blood glucose as result of supplementation with grapes, measured area under the curve for the period 300-420 min
Time frame: Up to two months
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