The Effects of Increasing Caloric Intake on Diet-Induced Thermogenesis and 24h Energy Expenditure

Study Description: Diet-Induced Thermogenesis (DIT) has been reported to increase as a function of the amount caloric intake. This study investigated this dose response between calorie intake and energy expenditure using a single liquid meal. By measuring EE over 24 hours in our respiratory chamber, we can capture the full extent of DIT at different caloric doses in relation to energy balance. Furthermore, we will investigate inter-individual differences in 24hEE response to different calorie loads. This is important as our previous studies demonstrated that individuals with greater EE during energy balance have 1) greater decrease in EE to fasting and 2) blunted EE response to higher calorie loads, in particular those with low protein content, respectively. Briefly, we will make multiple measurements of 24h EE in a whole-room indirect calorimeter, the gold standard measure of metabolism at multiple levels of energy intake relative to energy balance. These measures will be done at energy balance and in random order during fasting, 25, 50, 150 and 200% of energy balance requirements. Macronutrient balance for energy balance and lower calorie diets will be 50% carbohydrate, 30% fat, 20% protein; but for overfeeding will be 3% protein, 46% fat, 51% carbohydrate. The main goals of this research are to examine using state of the art measurement of DIT in a respiratory chamber whether there is indeed an association between caloric intake and energy expenditure and whether inter-individual response to calorie loads differs such that those with higher 24hEE during energy balance, have lower 24hEE during fasting and underfeeding 25 and 50% and lesser response to high calorie loads. The primary goal of this study is to investigate the impact of relative calorie load on diet-induced thermogenesis. Objectives: Primary Objective: a. To determine whether an association exists between diet-induced thermogenesis, 24hEE and calorie load relative to energy balance. Secondary Objectives: 1. To determine if participants with higher energy balance 24hEE adjusted for body composition, age, and sex have lower adjusted 24hEE to lower calorie loads (fasting, 25 and 50% of energy needs) 2. To determine if participants with higher energy balance 24h EE have lower adjusted 24hEE to high calorie loads with low protein overfeeding. 3. To assess changes in hormones known to be associated with changes in 24hEE (e.g., FGF21, ghrelin) 4. To assess changes in sympathetic nervous system activity based on changes in urinary catecholamines. 5. To assess changes in substrate oxidation rates at various dietary loads. Tertiary/Exploratory Objectives: 1. To assess whether psychosocial differences are associated with 24hEE responses to calorie loads. 2. Although our analytic plan and data collection procedure are meant to be all encompassing and comprehensive, our central exploratory, tertiary objective is to perform additional secondary data analyses in the future that answer additional research questions regarding diabetes and obesity risk that were not discussed in primary and secondary endpoints. These additional aims include, but are not limited to, associations of metabolic measures with psychosocial measures, hormonal endpoints, or future biomarker assayed at a later time point. Endpoints: Primary Endpoint: a. Diet induced thermogenesis, as calculated from 24h EE during feeding - 24h EE during fasting under different calorie loads Secondary Endpoints: 1. 24-hour energy expenditure during low calorie loads 2. 24-hour energy expenditure at higher calorie loads with low protein calorie loads 3. 24-hour energy expenditure during higher calorie loads with standard macronutrient mixed 4. FGF-21, ghrelin, and other appetitive hormones 5. Urinary catecholamines 6. 24-hour respiratory quotient, protein, carbohydrate, and lipid oxidation. Tertiary/Exploratory Endpoints: a. Psychosocial assessments, such as food insecurity and perceived stress