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Amylopectin Starch Induces Nonreversible Insulin Resistance in Rats¹

Human Nutrition Unit and Department of Biochemistry University of Sydney, Sydney, New South Wales 2006 Australia

Starches that are high in amylopectin are digested and absorbed more quickly than starches with a high amylose content and produce insulin resistance in rats during long-term feeding. The aim of this study was to determine whether amylopectin-induced insulin resistance could be prevented or reversed by a period of high amylose feeding. We employed a randomized design in which two groups of rats were fed either the high amylose and then the high amylopectin diet for two consecutive 8-wk periods or vice versa (high amylopectin and then high amylose). Four other groups were fed either a high amylose or a high amylopectin diet for 8 or 16 wk. All rats were fed two 10-g meals per day (300 kJ/d), and insulin sensitivity was assessed by intravenous glucose tolerance test (IVGTT) after 8 or 16 wk of feeding. We found no difference in glucose tolerance between any group at any time point. Insulin responses, however, were 50% higher (P < 0.01) after 16 wk of high amylopectin feeding [area under the plasma insulin curve (AUC) = 18.1 ± 1.4 nmol·L^-1·15 min] compared with high amylose feeding (AUC = 13.0 ± 1.2 nmol·L^-1·15 min). The two groups which received both diets developed a similar degree of insulin resistance, equivalent to that after 16 wk of high amylopectin feeding. The findings suggest that amylopectin-induced insulin resistance cannot be reversed or prevented by either a subsequent or previous period of amylose feeding. Taken together, the data suggest that the nature of starch in the Western diet influences the development of noninsulin-dependent diabetes mellitus in humans.

KEY WORDS: • starch • amylose • glycemic index • insulin resistance • rats

¹ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

² This work was conducted as partial fulfillment for the degree of B.Med.Sc. (Hons).

³ To whom correspondence should be addressed.

Manuscript received 25 July 1995. Revision accepted 30 October 1995.