PDF
(Download)
|
- Grape (Vitis vinifera) Seed Extract
- Metabolic Syndrome
- Oxidative Stress
|
Date:
06-28-2013 | HC# 021354-475
|
Re: Grape Seed Extract Consumed with Breakfast Reduces Levels of Plasma Glucose and Oxidative Stress in Patients with Metabolic Syndrome
Edirisinghe
I, Randolph J, Cheema M, et al. Effect of grape seed extract on postprandial
oxidative status and metabolic responses in men and women with the metabolic
syndrome – randomized, cross-over, placebo-controlled study. Functional Foods in Health and Disease.
2012;2(12):508-521.
Oxidative
stress and inflammation contribute to atherosclerosis and diabetes. A meal high
in carbohydrates and fat increases markers of oxidative stress and inflammation
postprandially (after eating). This effect is accentuated in patients with
obesity, diabetes, or metabolic syndrome. Fruits and vegetables high in
polyphenols may counteract this effect. The authors hypothesize that grape (Vitis vinifera) seed extract, which is
high in polyphenols, would attenuate meal-induced alterations in the oxidant
and inflammatory status of patients with metabolic syndrome. This hypothesis
was tested in a single-center, randomized, crossover, 2-arm, placebo-controlled
study conducted at the University of California, Davis.
Included
patients (n = 12; mean age = 45 years) had metabolic syndrome as defined by
having 3 of the following conditions: abdominal obesity, elevated serum
triglycerides, low high-density lipoprotein (HDL) concentration, elevated blood
pressure, and elevated blood glucose. They were non-smokers in general good
health. Excluded patients had clinical evidence and/or a history of
cardiovascular, respiratory, renal, gastrointestinal, metabolic, or hepatic
disease/conditions; used anti-inflammatory drugs, lipid-lowering medications, or
antioxidant supplements; were actively losing weight; or were addicted to drugs
and/or alcohol. Patients were recruited from newspapers, posters, and direct
contact in the Davis and Sacramento areas of California.
One
week prior to study commencement, patients were instructed to limit their consumption
of foods that contained polyphenols. They were acutely treated with 300 mg of grape
seed extract (MegaNatural® Gold; Polyphenolics; Madera, California)
or placebo (time = 0), 1 hour prior to eating a high-fat, high-carbohydrate
breakfast (670 kcal with approximately 40% energy from fat). The grape seed
extract contained 94.3 gallic acid equivalents (wt/wt) in total phenols. Blood
was collected at baseline and hourly for 5 hours postprandially. Blood was
analyzed for plasma lipids, glucose, insulin, oxidized low-density lipoprotein
(OxLDL), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α). After a
7- to 10-day washout period, the patients were crossed over to the other
treatment.
Peak
plasma hydrophilic and lipophilic oxygen radical absorbance capacity (ORAC)
occurred 1 hour postprandially in both groups and both were significantly
greater than baseline for both groups (P < 0.05). Postprandial ORAC values
in the hydrophilic phase (but not lipophilic phase) as assessed by positive
incremental area under the curve (AUC) was significantly increased with the grape
seed extract compared to the placebo (P < 0.01). Postprandial OxLDL and
glucose concentrations at 5 hours were significantly decreased in the grape
seed extract group (P < 0.01 and P < 0.05, respectively) compared to placebo.
The markers of inflammation (IL-6 and TNF-α) and insulin concentration were not
significantly different between groups postprandially.
The
authors conclude that grape seed extract enhanced the postprandial antioxidant
capacity of plasma, suppressed the increases in OxLDL, and reduced postprandial
glucose concentrations as compared to placebo in patients with metabolic
syndrome. It is unknown whether these changes would also occur following lunch
or dinner since the grape seed extract was only consumed acutely before
breakfast. Therefore, the data cannot be extrapolated to determine the effect
on long-term glucose/insulin control. The authors hypothesize that there was no
change in the inflammatory markers because the duration of the assessment was
too short. This study provides helpful preliminary research on the effect of
grape seed extract on postprandial antioxidant/glucose/insulin balance in
patients with metabolic syndrome.
—Heather S. Oliff,
PhD
|