The effect of viscous and fermentable dietary fiber consumption on adiposity, insulin resistance and fuel utilization in rats

Abstract

The incidence of obesity continues to be a major public health problem in the United States and comorbidities such as type 2 diabetes, cardiovascular disease and fatty liver that accompany obesity have dramatically increased over the last several decades. The health costs associated with the diagnosis and treatment of obesity-related disorders, particularly type 2 diabetes, are extraordinary and will be an enormous financial burden on the economy. Due to these dire circumstances, there is great interest in identifying foods that reduce the accumulation of adipose tissue and decrease the progression of insulin resistance. The consumption of dietary fibers that decrease the postprandial glucose curve is associated with decreased adiposity and a reduced incidence of type 2 diabetes, but it is controversial as to which property of dietary fiber is responsible for these effects. The objective of this research was to investigate the effect of increasing the small intestinal contents viscosity on the progression of obesity and type 2 diabetes. In the first study, non-fermentable hydroxypropyl methylcellulose (HPMC) was used to increase the small intestinal contents viscosity in a model of obesity with type 2 diabetes, the Zucker Diabetic Fatty rat. Rats fed HPMC showed improvements in insulin resistance and fatty liver but only a modest effect on reducing obesity. There was also a decrease in diabetic wasting as there was a greater food efficiency ratio and less urinary glucose excretion. In the second study, it was shown that adding barley flour containing a high concentration of viscous fermentable β-glucans had similar outcomes to those observed in the first study, including decreased insulin resistance and fatty liver, and a greater concentration of plasma adiponectin. In the third study, a model of diet-induced obesity was used to determine differences in fuel utilization when consuming viscous dietary fibers. Adding non-fermentable HPMC and fermentable guar gum to a high fat diet significantly decreased adiposity and fatty liver, yet there was no difference in insulin resistance. Consumption of both HPMC and guar gum increased the postprandial respiratory quotient compared to cellulose and also increased metabolic flexibility. There was no added effect of fermentability on any measure of adiposity, glucose control or fatty liver disease, indicating that SCFAs produced from fermentation had little or no effect on metabolic disease. In summary, the consumption of soluble dietary fibers that increase the viscosity of the small intestinal contents reduces the progression of obesity, insulin resistance and fatty liver, while the property of fermentation appears to have little discernable effect.