Rye bread decreases postprandial insulin response but does not alter glucose response in healthy Finnish subjects

Objective: To compare if postprandial glucose and insulin responses to wholekernel rye bread are lower than to wheat bread, and to see if these responses to two types of rye breads are different. To explore starch digestion in more detail, rate of starch hydrolysis of same breads was measured in vitro.

Design: Subjects were given test breads (43–61 g available carbohydrates by analysis) with standardized breakfast in a random order after a fast. Eight postprandial blood samples were collected during the following three hours. Rate of starch hydrolysis was determined by an in vitro enzymatic hydrolysis method.

Subjects: 10 men and 10 women, aged 32±3 and 27±5 y, BMI 24.5±2.2 and 20.3±1.1 kg/m², respectively, all had normal glucose tolerance.

Results: Plasma insulin response to wholekernel rye bread was lower than to wheat bread (45 min P=0.025, 60 min P=0.002, 90 min P=0.0004, 120 min P=0.050, 150 min P=0.033), but there was no difference in glucose responses. In comparison of two types of rye breads, glucose response to wholemeal rye bread at 150 and 180 min was higher (P=0.018 and P=0.041, respectively) and insulin response at 60 min was lower (P=0.025) than those to wholemeal rye crispbread. Total sugar profiles in vitro were similar for all breads. When free reducing sugars were subtracted, starch in wholekernel and wholemeal rye breads appeared to be hydrolysed slower than starch in wholemeal rye crispbread and wheat bread.

Conclusions: Wholekernel rye bread produces lower postprandial insulin response than wheat bread, but there is no difference in glucose response. The latter is in accordance with in vitro results. Postprandial glucose and insulin may also be affected by type of rye bread. Characteristics of different types of rye breads must be further investigated to develop health properties of rye breads.