We investigated the effects of high-monounsaturated fatty acid (MUFA) versus high-carbohydrate enteral formula on post-prandial plasma glucose concentration and insulin response in Japanese patients with type 2 diabetes mellitus and healthy Japanese volunteers. Ten healthy volunteers aged 20.8 +/- 1.2 years and 12 diabetic patients with good glycaemic control (glycosylated haemoglobulin < 7%) aged 58.6 +/- 7.7 years were randomly assigned to take high-MUFA or high-carbohydrate formula after a 12-h overnight fast. The patients switched to the other formula after 7 days. Post-prandial plasma glucose and insulin response were significantly lower in all subjects after taking high-MUFA formula compared with high-carbohydrate formula. No differences were observed in free fatty acids, triglycerides and plasma glucagon between the two diet groups. In conclusion, a high-MUFA enteral formula suppresses post-prandial hyperglycaemia without exaggerated insulin secretion compared with a high-carbohydrate enteral diet in patients with type 2 diabetes and healthy subjects.