capillaries. This blood flow structure is the result of a specifically ordered disposition of the RBCs surrounded by plasma in the microvessel lumen during flow in the capillaries and in the adjacent arterioles and venules up to approximately 15-20 μm wide [12]. The blood flow structure disturbances produce disordered blood fluidity during microcirculation because of increased blood flow resistance under conditions of constant, or even increased, pressure gradient. Based on perennial studies of blood flow disturbances inside the capillary microvessels, several primary factors that produce increased blood flow resistance in the narrowest blood vessels are as follows: enhancement of the RBC aggregation, lowered RBC deformability, increased local hematocrit and increased local blood plasma viscosity. The impact of a hypocaloric diet on the hemorheology of obese patients has been reported in numerous studies [2,13-17]. Several studies concerned with the influence of a hypocaloric diet on RBC aggregation in obese patients reported that weight loss after dieting in obese patients normalized the aggregation of the RBCs, affecting a corresponding improvement in the erythrocyte aggregation index [13-15]. Other authors have showed the absence of improvement in rheological parameters, including RBC aggregation, after weight loss associated with a low-calorie diet [2,16]. Sola et al. (2004) showed that a very low-calorie diet of 458 kcal/day reduced erythrocyte aggregation in one month; however, a prolonged lowcalorie diet (1500 kcal/day) did not provide additional benefit for red cell aggregation, which returned to its basal value after 3 months of follow-up [17]. The impact of a hypocaloric diet on the obese patients’ blood and plasma viscosities are also not conclusive. According to Poggi et al. [14], after three months of a 500-kcal/day diet, there was a reduction in blood viscosity at low shear rates by significant decreases in RBC aggregation and hematocrit levels. Fanari et al. (1993) also demonstrated that weight loss after dieting in obese patients contributed to improving plasma and blood viscosity [13]. Other studies have shown an absence of improvement in blood and plasma viscosity after weight loss associated with a low-calorie diet [14,15]. The results of research on the impact of diet on hemorheology indicated that a beneficial effect of weight loss on rheological profiles depends on the amount of weight lost and its long-term maintenance. Bariatric surgery is recognized to substantially improve body weight, obesity-associated co-morbidities and long-term survival. The influence of weight loss surgery on hemorheological parameters has been investigated in several publications. In our first papers, verticalbanded gastroplasty was shown to induce several beneficial changes Abstract