The Effect of Soybean Flour on the Glycemic Index, Glycemic Load, and Satiety Index of White Bread in Healthy Individuals

Background: This study examines the impact of whole soybean flour on the Glycemic Index (GI), glycemic load (GL), and Satiety Index (SI) of white wheat bread. Methods: In a randomized crossover study, 10 healthy women fasted on four separate days, one week apart, and consumed one of three types of bread (white bread, or breads with 25% and 50% soybean flour) or a glucose solution. Blood glucose levels, the GI, and GL were calculated at specific intervals postprandial. Over three days, 23 healthy women assessed satiety after consuming the bread, with a week between sessions, using a Visual Analog Scale (VAS) Questionnaire to evaluate satiety during fasting and at 15-minute to two-hour intervals postprandial. Results: The area under the blood glucose curves significantly decreased after consuming 50% soy bread compared to white bread (P = 0.002). Blood glucose levels significantly decreased after consuming soy flour bread, especially the 50% soy flour variant, compared to white bread (P < 0.05). The GI of the 50% soy flour bread was also significantly lower than that of white bread (P = 0.004). Adding 25% and 50% soy flour to white bread reduced the GI by 14% and 36.5%, respectively. Both 25% and 50% soy flour breads had significantly lower GL than white bread (P = 0.001), with reductions of 26% and 65%, respectively. Both 25% and 50% soy flour breads showed significantly higher satiety curve areas compared to white bread (P = 0.001). Incorporating 25% and 50% soy flour into white bread increased its SI by 168% and 226%, respectively (P < 0.05), compared to white bread (P = 0.002). Conclusions: Incorporating soybean flour into white bread lowers its GI and GL while enhancing satiety. Given the potential benefits of low GI foods, soy-enriched bread could be clinically important for prevention of metabolic diseases.