The effect of a 50 g starch meal prepared with pre-cooked instant bean flakes on glucose and insulin plasma levels and on glucose oxidation rate as measured by continuous indirect calorimetry was assessed in six healthy human volunteers during 4 h following the meal. Comparison was done with the same load of starch as potato flakes to which the fiber and protein content of the bean meal had been added. Thirty minutes after ingestion, plasma glucose and insulin rise was less after beans than after potatoes (0.4 +/- 0.2 vs 2.0 +/- 0.3 mmol . l-1), p less than 0.01, and 8 +/- 2 vs 38 +/- 5 microU . ml-1, p less than 0.001). The elevation of glucose oxidation was markedly less during the 2 h following the ingestion of beans when compared to potatoes. The bean flakes meal gave rise to only moderate elevation of plasma glucose and insulin levels and of glucose oxidation rate when given to four noninsulin-dependent-diabetes mellitus patients. It is suggested that the slow carbohydrate property of legumes is not due to their fiber content, but might be related to the histological structure of the seed.