Post-lunch resting and exercise metabolism following high-fat and high-carbohydrate breakfast

Abstract

Introduction. The aim of this research was to identify the effect of breakfast macronutrient composition on second meal and evening exercise substrate utilisation. The hypothesis of this study was that a high fat breakfast would lead to increased fat utilisation throughout the rest of the day in both resting and exercise, and a high carbohydrate breakfast would lead to increased carbohydrate utilisation throughout the rest of the day in both resting and exercise. Methods. 17 subjects completed a baseline trial and two feeding trials; high carbohydrate (porridge) and high fat (avocado based smoothie). The baseline trial consisted of resting energy expenditure using indirect calorimetry and VO2 max test. The feeding trials consisted of the trial breakfast (carbohydrate or fat), a standardised lunch, followed by resting indirect calorimetry and blood glucose measurements, and then finished with an early evening graded exercise test. Substrate utilisation was estimated during rest and during exercise tests with indirect calorimetry. Results. Following carbohydrate breakfast RER was significantly higher during rest after lunch (carbohydrate:0.89±0.07 vs fat:0.85±0.07; p=0.026). Blood glucose was significantly higher up to 2 hours after lunch following the high fat breakfast (carbohydrate:6.29±0.79mmol/L vs fat:6.94±1.15 mmol/L; p=0.018). There were no significant differences between breakfast compositions in RER during evening exercise. Conclusion. An isocaloric high fat breakfast alters substrate utilisation at rest following a second meal but does not influence fuel selection during early evening exercise. A high fat breakfast impairs glucose tolerance up to 2 hours after the second meal.