Pulses, which are the edible seeds of leguminous plants, have been part of the human diet for centuries and are being strongly recommended by physicians, dietitians, and nutritionists to be components of a healthy balanced diet due to their nutritional quality. Lentils are a type of pulse and are a rich source of nutrients, being particularly high in protein, starch, and dietary fiber, which have been shown to promote certain health benefits, such as reducing postprandial glycemia and subsequent food intake (second meal effect). However, it remains unclear as to which component(s) are responsible for the ability of lentils to lower postprandial blood glucose levels or promote satiety after consumption. To address this question, the present study examined the effects of consuming commercially prepared lentil fractions (fiber, starch, and protein) on subjective appetite, blood glucose (BG) and insulin before and after a pizza meal, served at two different times, in healthy young men.
Two randomized, cross over, repeated measures experiments were conducted in this study. Forty eight healthy males consumed iso-volumetric (300 ml) soup alone, which served as the control, or with the addition of 20 g of one of the following lentil fractions: protein isolate, protein concentrate, starch, or fiber. Treatment consumption was followed by serving the participants a fixed energy pizza meal (12 kcal/kg body weight), which was served at 30 minutes (exp-1) or 120 minutes (exp-2) following the treatments. Subjective appetite, BG and insulin were measured during both pre-meal and post-meal periods.
In experiment 1, with the exception of lentil starch, which caused an increase in BG, there was no effect of treatment on pre pizza meal BG compared to the control. The lentil protein isolate and lentil protein concentrate, but not lentil starch or lentil fiber, treatments lowered post-meal glycemia compared to the control (P<0.0001) without a significant surge in insulin concentrations. No effects were seen on pre-meal measures of satiety; however, post-meal BG and subjective appetite were lower (P<0.05) after consumption of both lentil protein isolate and concentrate compared to the control. In contrast to our findings in experiment 1, lentil starch resulted in lower pre- and post-meal subjective appetite compared to the control in experiment 2 (P<0.05); however, consumption of lentil starch also led to higher BG values. No effects were observed after consumption of the lentil fiber fraction, which is likely due to fiber exerting more long-term physiological effects (observed at > 170 mins) and may also be due to lentils having a higher concentration of insoluble vs soluble fiber.
The beneficial effects of lentil consumption are attributed by the lentil protein fractions, which are responsible for reducing BG immediately after the pizza meal as well as promoting short term regulation of satiety. Lentil starch on the other hand elicited a more prolonged second-meal effect on appetite. The findings of this study highlight the importance of including lentils as part of an everyday diet. Moreover, the fractions themselves in isolated form, may serve as value-added ingredients when incorporated into commonly consumed foods.
Project lead: Dr. Harvey Anderson (416) 978-1832 email@example.com