In the last years the use of alimentary fibres in dietetic management of diabetic patients increased. The aim of this work was to evaluate, in type 2 diabetic subjects, the glycaemic and insulinemic increments after a standard breakfast with glucomannanos enriched biscuits and with common slices of toast containing the same amounts of carbohydrates and calories. The basal serum values of glucose and C-peptide were similar in the two days of the test. The mean increments of glucose and C-peptide were significantly higher (p < 0.001) after slices of toast than after glucomannanos enriched biscuits. In conclusion our results show a reduction in glycaemic increments after breakfast with glucomannanos-biscuits. The decreased insulin secretion and the reduction of insulin need can longer preserve the functional reserve of beta-cells.