People who are overweight, particularly those with excess central adipose tissue, are at risk of developing dysfunctions in lipid and glucose metabolism resulting in a propensity for cardiovascular disease and/or type-2 diabetes. This cluster of symptoms, which includes elevated blood pressure, elevated fasting blood glucose levels, elevated triglycerides and reduced levels of high-density lipoprotein cholesterol, has been defined as metabolic syndrome.
Oxidative stress, which is an imbalance between the generation of free radical species and the activity of anti-oxidant defense mechanisms, is thought to be one of the underlying mechanisms behind the risk of cardiovascular disease and diabetes associated with obesity. Subjects who are obese are more likely to have higher levels of oxidative stress than those of normal weight. In addition, weight loss is associated with a decrease in oxidative stress. Further, analysis of endogenous anti-oxidant protection in subjects with metabolic syndrome indicate that it is depressed. And, subjects with metabolic syndrome also tend to display an increase in oxidative damage, measured as elevated lipid peroxidation and elevated protein carbonyls. Oxidative stress has also been shown to enhance insulin resistance and it has been suggested that antioxidant therapy may reduce insulin resistance in diabetic patients[4, 5].
Diets which are high in fruits and vegetables, are reported to increase plasma antioxidant capacity. In addition to vitamins C, E and beta-carotene, fruits and vegetables contain phenolic compounds that contribute to their antioxidant capacity. The inverse relationship between fruit and vegetable intake and the risk of cardiovascular diseases and diabetes has been associated with antioxidant capacity of these foods and in their phenolic content[8, 9]. Preclinical studies have reported that polyphenolics compounds have beneficial effects on glucose absorption, insulin levels and lipid metabolism.
The fruit of the açaí palm (Euterpe oleracea Mart.), which is native to South America has recently become popular as a functional food due to its antioxidant potential. The edible fruit is round, black-purple in color, about 1-inch (25 mm) in diameter and contains a single large seed. Macerating the pulp of the fruit produces a viscous liquid which is approximately 2.4% protein and 5.9% lipid (by weight). Analysis of fatty acid composition reveals that monounsaturated oleic acid is the primary fat, present at 56.2%, followed by palmitic (saturated fatty acid; 24.1%) and linoleic acid (polyunsaturated; 12.5%). Analysis of phenolics in the fruit revealed the presence of anthocyanin 3-glycosides, ferulic acid, epicatechin, p-hydroxy benzoic acid, gallic acid, protocatechuic acid, catechin, ellagic acid, vanillic acid, p-coumaric acid and gallotannins. Cyanidin-3-monosaccharides are reported to be present in the fresh pulp at a concentration of 1040 ± 58 mg/L. More specifically, the glucosides cyanidin-3-rutinoside and cyanidin-3-glucose, were measured at concentrations of 1.93 and 1.17 mg/g dry weight, respectively, with a total anthocyanin content of 3.19 mg/g dry weight. Açai pulp is reported to have an antioxidant capacity of 48.6 μmol Trolox equivalents (TE)/ml as measured using the oxygen radical absorbance capacity (ORAC) assay. Anthocyanins are generally considered to be the major contributors to the antioxidant activity of the pulp. However this concept has been challenged by a group of researchers who estimated the contribution of the anthocyanins to be just 10% of the total in vitro antioxidant capacity and suggested that other, unidentified, antioxidant constituents exist in the fruit. This group of researchers compared the Total Oxidant Scavenging Capacity (TOSC) values for cyanidin-3-glucoside and cyanidin-3-rutoside to their corresponding concentrations in açaí preparations and found that the açaí preparations had significantly higher TOSC values than the calculated capacity due to constituent cyanidin glycosides.
In addition to the in vitro assays, the antioxidant potential of preparations of açaí pulp and juice has also been reported in animal and human studies. Experiments with rats revealed that a diet supplemented with 2% açai pulp (dry wt/wt) for 6 weeks caused a reduction in protein oxidation compared to control animals. Protein oxidation was measured as a decrease in carbonyl protein and an increase in protein sulfhydryl groups. There were also beneficial effects, compared to controls, on antioxidant enzyme activity, measured as an increase in serum paraoxonase, which is associated with prevention/inhibition of lipoprotein oxidation. In animals fed a hypercholesterolemic diet with or without açai pulp, there was a decrease in serum superoxide dismutase (SOD) activity compared to controls. SOD is an enzyme which is induced in response to oxidative stress and converts superoxide radicals into hydrogen peroxide. In humans, plasma anti-oxidant capacity (measured using the ORAC assay) in humans increased up to 3 fold with a single dose of 7 ml açaí pulp/kg body weight compared to the control beverage (p < 0.01), with a t-max of 3 hours. The maximum plasma concentration (Cmax) of total anthocyanins, measured as cyanidin-3-glucoside was reached 2.2 hours after consumption of the pulp.This pharmacokinetic study included healthy volunteers, who were dosed after a 72 hour dietary washout phase and an overnight fast. The subjects consumed a diet low in antioxidants that excluded the majority of dietary polyphenolics. The antioxidant capacity was measured as the ratio of TE for each time point compared to baseline, divided by the dose volume administered to the subject.
As previously stated, reducing the production of reactive oxygen species is hypothesized to assist in the normalization of metabolic pathways that lead to the onset of diabetes, endothelial dysfunction and cardiovascular disease. In a test of that hypothesis, this pilot study was designed to evaluate the effects of a proprietary preparation of açai pulp in overweight subjects who are at risk for developing metabolic syndrome. Several studies have been conducted on the effects on açai preparations in vitro and in animals, but little is known about its effects on humans. Epidemiological and experimental studies point to the potential benefits of antioxidants in ameliorating the risks of cardiovascular disease and diabetes type II, however the results from clinical studies with antioxidant vitamins have been equivocal. The study measured endpoints before and after administration of açai pulp for one month. Measurements included levels of fasting plasma glucose, insulin, cholesterol and triglycerides. Exhaled (breath) nitric oxide metabolites (eNO) and plasma levels of high sensitivity C-reactive protein (hs-CRP) were measured as indicators of inflammation. The response of blood glucose, blood pressure and eNO to a standardized meal was also determined.