An In Vitro Study on the Effects of Selected Natural Dietary Fiber from Salad Vegetables for Lowering Intestinal Glucose and Lipid Absorption

Background: Salad vegetables are good sources of dietary fiber and are becoming increasingly popular among consumers. Therefore, these plants have the potential to be developed as functional foods. Objective: Using an in vitro model, this study investigated the physical properties and intestinal glucose and lipid absorption capacities of dry dietary fiber from vegetables typically consumed in salads (types of lettuce, including red oak, red coral, green oak, butterhead, and cos). Method: Fiber was prepared from each type of lettuce using an enzymatic method and then characterized. Physical properties, including solubility and water-binding, swelling, cation-exchange, and oil-binding capacities, and antihyperglycemic and antihypercholesterolemic effects of fiber were investigated. Results: The hydration capacity of total dietary fiber and insoluble fiber from the majority of sources was significantly different from that of cellulose. Adsorption and diffusion of glucose were directly proportional to incubation time, and the diffusion rate was significantly lower in the treatments containing fiber compared to the cellulose control. Fiber from these vegetables also inhibited amylase and alpha-glucosidase activities. Moreover, fiber from all sources exhibited significantly higher sodium cholate and cholesterol-binding capacity compared to cellulose, and also retarded pancreatic cholesterol esterase activity in a concentration-dependent manner. Conclusion: This study demonstrates that natural dietary fiber from salad vegetables can reduce glucose and lipid absorption and breakdown rates, thus preventing increases in postprandial blood glucose and cholesterol levels, which can be beneficial to human health.