Effects of Ordered Eating on Various Postprandial Measures

Postprandial glucose (PPG) is an indicator of acute and chronic overall health, and aberrations in glucose, insulin, and other postprandial (PP) markers are common in obesity and cardiometabolic disorders. Chronically elevated glucose can lead to a number of health problems such as type 2 diabetes mellitus. Additionally, PPG responses can impact substrate utilization responses to exercise, which may have implications for both healthy and diseased populations. One potentially simple lifestyle modification to alter PPG and related markers is to change the order in which foods are consumed within meals. The purpose of this dissertation was to further explore the impact of ordered eating on a variety of PP measures and its possible effects on exercise responses in an acute setting. Study 1 was a systematic review of existing literature to assess the effect of ordered eating on a variety of PP measures including glucose, insulin, C-peptide, hunger, and satiety. Study 2 was a randomized crossover laboratory-based experiment that examined the effects of ordered eating on PPG, substrate utilization, hunger, satiety, and other variables surrounding an exercise bout. For Study 1, three databases were searched, reference lists of identified reports were searched, and an author of several studies was consulted to verify that relevant literature was included. The review included acute interventions that administered isocaloric meals of the same foods but with foods eaten in different orders. Participants for Study 2 were recreationally active, generally healthy adults aged 18 to 60 years old and had fasting blood glucose measured as well as resting gaseous exchange before being given a standard meal consisting of chicken, broccoli, and rice, which was ordered in a rice first (RF) condition on one day and a rice last (RL) condition on a different day. Following the meal, participants rested for 60 minutes prior to beginning a 30-minute exercise bout at 70% of maximum heart rate. Throughout rest and exercise, participants rated hunger, appetite, satiety, and fullness and had gaseous exchange and blood glucose measured regularly. The main statistical analysis for study 2 was a two-way ANOVA with time and condition as within-subject factors to compare the RL and RF conditions. Results, in brief, showed that there was a significant effect of meal order throughout the literature, on PPG and PP insulin—consuming carbohydrate-dense foods last in meal sequence leads to lower glucose and insulin excursions on average. Glucagon like peptide-1 area under the curve was also generally higher when carbohydrate was consumed at the end of a meal. Still, evidence around incretin, gut hormone responses, and perceptual measures was generally of low or very low quality, leaving gaps for further research. Within the lab study, the impact on PPG was successfully replicated, and there was also an effect of meal sequence on substrate utilization—a RF sequence led to higher utilization of carbohydrate both at rest and during exercise. In sum, this dissertation demonstrates that the relatively novel approach of altering the meal sequence may have significant implications relating to blood glucose and substrate utilization.