High-fiber rye bread and insulin secretion and sensitivity in healthy postmenopausal women

Background: Fiber and whole-cereal intakes may protect against hyperinsulinemia and the risk of type 2 diabetes.

Objective: The aim was to study whether the long-term use of high-fiber rye bread and white-wheat bread modifies glucose and insulin metabolism in healthy postmenopausal women.

Design: The study was a randomized crossover trial consisting of 8-wk test and 8-wk washout periods. The subjects were 20 postmenopausal women [x̄ ± SD age: 59 ± 6.0 y; body mass index (in kg/m²): 27.5 ± 2.9; baseline fasting serum cholesterol: 6.5 ± 0.8 mmol/L], of whom 3 had impaired glucose tolerance as determined by a 2-h oral-glucose-tolerance test. The test breads were high-fiber rye and white-wheat breads, planned to make up ≥20% of energy. Fasting blood samples were collected for the measurement of plasma glucose and insulin at the beginning and at the end of both bread periods. The frequently sampled intravenous-glucose-tolerance test was performed at the run-in and at the end of both bread periods. The acute insulin response, insulin sensitivity, and glucose effectiveness were calculated.

Results: The rye bread made up 23.4 ± 4.3% and wheat bread 26.7 ± 8.2% of total energy intake. Compared with that during the run-in period, the acute insulin response increased significantly more during the rye bread period (9.9 ± 24.2%) than during the wheat bread period (2.8 ± 36.3%; P = 0.047). Other measured variables did not change significantly during the study.

Conclusions: Modification of carbohydrate intake by high-fiber rye bread did not alter insulin sensitivity in postmenopausal, hypercholesterolemic women. High-fiber rye bread appears to enhance insulin secretion, possibly indicating improvement of b cell function.