The Effects Of A High Vs. Low Carbohydrate Pre-fast Meal On Incretin Hormone Secretion: A Randomized Crossover Study

Recently, fasting has gained popularity as a means of preventing chronic illness through weight loss and other health benefits. Specifically, fasting-induced changes in incretin hormones such as glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) may aid the body in regaining insulin sensitivity, improving blood glucose control, and preventing chronic disease. PURPOSE: The purpose of the study was to determine the impact of an acute 24-hour fast initiated with either a low carbohydrate (LC) or high carbohydrate (HC) meal on GIP and GLP-1 plasma levels. METHODS: A randomized crossover study design was implemented. Participants (n = 24) were sedentary, overweight (BMI >27) and 50+ years old. Each completed two 24 hr fasts initiated with either a HC or LC meal. Venous blood draws were taken at baseline, 1 hr (post-meal), at 24 hrs, and 48 hrs (24 hrs post-fast) to show changes in GIP and GLP-1. RESULTS: Levels of GIP and GLP-1 both changed over time (p < 0.0001) and showed differences between conditions (p = 0.0362 and p = 0.0135, respectively), but only GLP-1 showed a significant time by condition interaction (p = 0.0001). Both GIP and GLP-1 (p = 0.0001) were elevated 1 hr into the fast in both conditions. GLP-1 (p < 0.0001) was higher in the LC condition compared to the HC condition at 1 hour. There were no significant differences between conditions for GLP-1 at 0, 24 or 48 hrs. CONCLUSIONS: The macronutrient content of the pre-fast meal of an acute fast may modestly affect incretin levels over the period of 24 hrs. Both incretin hormones spiked postprandially. The LC condition caused a greater increase in incretin hormones than the HC condition at the 1 hr postprandial spike. Most levels had returned to baseline by the 48 hr mark. These findings warrant more research on how long-term fasting and varying meal interventions could further affect incretin secretion.