[Problem]To provide: a substance and a method both for effectively preventing the worsening of insulin resistance or for ameliorating insulin resistance； a method for treating diabetes, impaired glucose tolerance, obesity, hyperlipemia, arteriosclerosis, hypertension, a heart disease or metabolic syndrome； and a method for preventing these diseases.[Solution]An agent for preventing the worsening of insulin resistance or for ameliorating insulin resistance, which contains 1-kestose as an active ingredient. According to the present invention, it becomes possible to prevent the worsening of insulin resistance or ameliorate insulin resistance in a human or animal body conveniently and effectively without little concerning about adverse side effects or safety. According to the present invention, it also becomes possible to prevent or treat diabetes, impaired glucose tolerance, obesity, hyperlipemia, arteriosclerosis, hypertension, a heart disease or metabolic syndrome by preventing the worsening of insulin resistance or ameliorating insulin resistance in a human or animal body.
