Impacts Of Initiating A Fast With A Low Verses High Carbohydrate Shake On Glycemic Control

PURPOSE: While fasting has received attention as a strategy to improve glycemic control, these benefits may vary depending on the macronutrient content used to initiate a fast. The purpose of this study was to understand how macronutrient composition of the fast-initiating meal influences markers of glycemic control throughout a 24-hour fast in older, sedentary adults with abdominal obesity. METHODS: Each of the 24 participants (13 male, 11 female) completed two 24-hour fasts (8:00 am to 8:00 am) with a washout period of 6-10 days. To initiate each fast, participants were provided either a low carbohydrate protein shake or an isocaloric high carbohydrate protein shake (592.13 ± 104.57 kcal). Plasma samples were obtained immediately prior to shake consumption, 1-hour post-shake consumption, and at the conclusion of the 24-hour fast. Capillary beta-hydroxybutyrate (BHB) was measured at the same time points, with additional readings at 4, 8, and 12 hours of fasting. Continuous glucose monitors were used to observe glucose levels. RESULTS: Area under the curve analysis was used to assess differences in overall glucose and BHB concentrations between conditions. A mixed effects model with repeated measures was used to assess the effects of the fasting conditions for insulin and glucagon. Glucose concentrations were 47.13% higher (p = 0.013) and ketone concentrations were 63.93% lower (p = 0.0028) in the high carbohydrate condition over a 24-hour period. There was a significant condition-by-time interaction for insulin and glucagon (p < 0.0001). At 1-hour post-shake consumption, insulin was 2667.24 ± 439.74 pg/dL higher and glucagon was 36.93 ± 15.19 pg/dL lower in the high carbohydrate condition. CONCLUSIONS: This study of older, sedentary adults with abdominal obesity showed that the macronutrient composition of a pre-fasting meal can influence the metabolic response during the fasting period. Initiated a fast with a low carbohydrate meal may enhance the benefits of nutritional ketosis and glycemic control. This may have implications for the use of intermittent fasting for older adults. Mentoring Environment grant from Brigham Young University