Abstract
Objective:Yacon is a perennial plant forming a clump of >20 big, edible underground tubers. Yacon, which originates from South America, has become increasingly popular in the Japanese diet for tubers have a lower caloric value and a high fiber content. Recent studies have suggested that yacon feeding ameliorates diabetes as indicated by reduced blood glucose.Methods:We fed male Zucker fa/fa rats for 5 weeks with isocaloric normal chow diet containing from 6.5% control aroid or 6.5% yacon. Insulin sensitivity was evaluated by euglycemic-hyperinsulinemic clamp study.Results:Body weight was comparable between yacon- and aroid-fed rats. In the basal state, yacon feeding had an effect to lower fasting glucose levels from 184.1±4.1 to 167.8±2.7 mg dl−1 (P<0.01), as well as basal hepatic glucose output (HGO) from 9.9±0.4 to 7.4 ± 0.2 mg kg−1 per min (P<0.01). During the clamp studies, the glucose infusion rate required to maintain euglycemia was increased by 12.3% in yacon-fed rat. The insulin suppression of HGO was also increased in yacon-fed rats compared with control rats (85.3±2.4% vs 77.0±3.0% P<0.05), whereas the glucose disposal rate was not different between the two groups. Consistent with the clamp data, the insulin-stimulated phosphorylation of Akt was significantly enhanced in liver but not in skeletal muscle. Furthermore, tribbles 3 (Trb3) expression, which is a negative regulator of Akt activity, was markedly reduced in the liver of yacon-fed rats compared with control rats.Conclusion:These results indicate that the effect of yacon feeding to reduce blood glucose is likely due to its beneficial effects on hepatic insulin sensitivity in the insulin resistant state.
Highlights
Type 2 diabetes mellitus is characterized by insulin resistance and b-cell dysfunction, the balance between which varies widely between individuals
Homeostasis model assessment insulin resistance, which evaluates the insulin sensitivity, was significantly decreased (Po0.01) in the yacon group compared with the control group, suggesting an improvement of insulin sensitivity after 5 weeks of yacon feeding
As skeletal muscle accounts for the great majority of GDR, these results indicate that yacon feeding does not affect insulin sensitivity in skeletal muscle
Summary
Type 2 diabetes mellitus is characterized by insulin resistance and b-cell dysfunction, the balance between which varies widely between individuals. Insulin resistance, which is characterized by an impaired ability of insulin to inhibit glucose output from the liver and to promote glucose uptake in muscle, is frequently well established in individuals with impaired glucose intolerance. It is the concomitant presence of b-cell dysfunction that distinguishes those in whom glucose intolerance worsens from those in whom it remains stable. Interventions that decrease insulin resistance and preserve or improve b-cell function are likely to be effective in slowing progression from impaired glucose intolerance to diabetes, or even allowing reversion to normal glucose tolerance. Dietary interventions can be an effective tool to prevent or treat insulin resistance and type 2 diabetes mellitus.
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