We examined in rats whether or not the prolonged ingestion of recrystallized amylose (RCA) would prevent the development of insulin resistance. Rats were fed on a diet containing waxy cornstarch (WCS) as carbohydrate or a diet containing 30% RCA in place of WCS for 18 wk. Glucose tolerance test (GTT) was conducted at every four weeks. On wk 16, the plasma insulin response as assessed by the area under the curve was lower in the RCA diet group than in the WCS diet group. The fasting plasma insulin level tended to increase over time in both groups, but was lower in the RCA diet group on wk 16. An autopsy revealed that the adipose tissue mass and serum free fatty acid concentrations were significantly higher in the WCS diet group. The results suggest that prolonged ingestion of RCA had the effect of slowing the development of insulin resistance through a lower concentration of serum free fatty acids, presumably due to the prevention of adipocyte hypertrophy.