OBJECTIVETo assess the clinical efficacy of nutritional amounts of grape polyphenols (PPs) in counteracting the metabolic alterations of high-fructose diet, including oxidative stress and insulin resistance (IR), in healthy volunteers with high metabolic risk.RESEARCH DESIGN AND METHODSThirty-eight healthy overweight/obese first-degree relatives of type 2 diabetic patients (18 men and 20 women) were randomized in a double-blind controlled trial between a grape PP (2 g/day) and a placebo (PCB) group. Subjects were investigated at baseline and after 8 and 9 weeks of supplementation, the last 6 days of which they all received 3 g/kg fat-free mass/day of fructose. The primary end point was the protective effect of grape PPs on fructose-induced IR.RESULTSIn the PCB group, fructose induced 1) a 20% decrease in hepatic insulin sensitivity index (P < 0.05) and an 11% decrease in glucose infusion rate (P < 0.05) as evaluated during a two-step hyperinsulinemic-euglycemic clamp, 2) an increase in systemic (urinary F2-isoprostanes) and muscle (thiobarbituric acid–reactive substances and protein carbonylation) oxidative stress (P < 0.05), and 3) a downregulation of mitochondrial genes and decreased mitochondrial respiration (P < 0.05). All the deleterious effects of fructose were fully blunted by grape PP supplementation. Antioxidative defenses, inflammatory markers, and main adipokines were affected neither by fructose nor by grape PPs.CONCLUSIONSA natural mixture of grape PPs at nutritional doses efficiently prevents fructose-induced oxidative stress and IR. The current interest in grape PP ingredients and products by the global food and nutrition industries could well make them a stepping-stone of preventive nutrition.

The present review focuses on the past and recent knowledge in the field of exercise hemorheology and presents some unresolved issues for opening discussion. Acute exercise is associated with a rise in hematocrit which results in an increase in blood viscosity. Whereas increased blood viscosity was previously viewed as having negative consequences for cardiovascular function and aerobic performance, recent findings suggest dynamic changes in blood viscosity might be useful for vascular function during exercise by increasing nitric oxide production. Other determinants of blood viscosity are altered by exercise (e.g., decreased red blood cell deformability, increased red blood cell aggregation and plasma viscosity) and may, independent of the associated effect on blood viscosity, directly modulate aerobic capacity. However, the data published on the effects of exercise on the hemorheology are not consistent, with some studies showing decreased, unchanged, or increased red blood cell deformability/aggregation when compared with rest. These discrepancies seem to be related to the exercise protocol investigated, the population tested or the methodogy utilized for hemorheological measurements. Finally, this review focuses on the effects of exercise training (i.e. chronic physical activity) on the hemorheological profile of healthy individuals and patients with cardiovascular and metabolic disorders. P. Connes et al. / Blood rheology and exerciseaddress classical findings in exercise hemorheology and will present new directions. In addition, some unresolved issues will be presented for opening discussion. Acute effects of exercise on hemorheology and relationships with performance2.1. Blood viscosity P. Connes et al. / Blood rheology and exercise 189 PRE 90 Blood viscosity (mPa/s) POST 90 POST 225 5 6 7 8 9