PURPOSE: To evaluate whether the modification of ingredients of two bakery products, muffins and bread, reduces their glycemic index, by means of in vitro and in vivo procedures. METHODS: In vitro and in vivo glycemic index were evaluated for two types of bread and two types of muffins including one standard product for each category. For the in vitro determination, kinetics of starch digestion method was used. For the in vivo procedure, postprandial glucose measured as IAUC was obtained in a group of eighteen healthy volunteers (ten did the test with muffins and eight with breads). RESULTS: In in vitro, a reduction in the expected glycemic index regarding the control muffin was achieved with the partial substitution of wheat flour by a mixture of resistant starch, dextrin and lentil flour. In breads, with the partial substitution of wheat flour by a mixture of resistant starch and dextrins, a decrease in the expected glycemic index was also observed. In in vivo, a reduction in GI was also achieved both in muffin and in bread. All the obtained GI was higher in in vitro method. CONCLUSIONS: Despite the fact that in vitro overestimate in vivo method, the trend in the reduction in GI seems to be similar in both methods. With the substitution assayed, a reduction in the expected glycemic index and the glycemic index were obtained both in muffins and in breads.