Date of Award

12-15-2014

Document Type

Open Access Dissertation

Department

Exercise Science

First Advisor

Steven N. Blair

Abstract

Energy balance is the result of a dynamic relationship between energy intake (EI), energy expenditure (EE) and energy storage (ES). These three components of energy balance have extremely complicated associations, and all three major components are consistently influenced by physiologic, psychological, and sociologic factors. Concerted changes between EE and EI result in alterations of the ES. Most often in clinical and research settings, bodyweight is used as marker of body composition (i.e., ES) changes. Traditional measurements of bodyweight do not give an accurate portrayal of ES change or the role it has in energy balance. This dissertation supplies new methods of monitoring ES that better estimate an individual’s true change in ES over time. These new methods were then applied and used to categorize weight gain, loss and maintenance. Further, the association between these categorizations and EE was investigated. Thus this dissertation begins with an investigative analysis of one component of energy balance and then progresses to the association between two components and the overall influence of the association on energy balance. The three papers of this dissertation examine 1) the overall bodyweight changes that occur over a year period in healthy adults 2) the overall body composition changes that occur over a year period in healthy adults; and 3) the associations of bodyweight and composition changes with average energy expenditures over a year period. This dissertation used clinical measurements of bodyweight, composition and objectively measured EE values, which were collected as a part of the first year of the Energy Balance Study (a comprehensive study designed to determine the associations of caloric intake and EE on changes in bodyweight and composition in a population of healthy men and women). The aims of the current dissertation are crucial to providing insight and results for the primary aim of the Energy Balance Study. The first study revealed that the participants of the Energy Balance Study are on average gaining roughly a kilogram (kg) of bodyweight over a year period, which is similar to estimates that have been made for the United States (US) population. However, while 43% of the participants were found to be gaining weight, a greater majority (46%) were maintaining bodyweight over the year period. The participants gaining and losing the most weight were substantially heavier than those who maintained bodyweight. Lastly, when the traditional measurements of monitoring bodyweight were compared to linear mixed model estimations of bodyweight change they were found to largely over or underestimate changes in the individual. Study two showed that the average bodyweight the participants from the Energy Balance Study gained (roughly 1kg) was predominantly due to increases in fat mass (FM). Subsequently, on average the group gained slightly less than 1 kg of FM in a year period. Similar to the trends seen in bodyweight changes, the greatest majority of participants were considered to be maintaining fat mass. While overall the fat-free mass (FFM) of the participants did not change substantially it was negatively correlated with FM. In the last study overall total daily EE was shown to be substantially elevated in the participants considered as weight gainers and participants considered as fat-gainers.

However, the elevated total daily EE was most likely due to the substantially heavier starting bodyweight of these two groups. When the total daily EE was analyzed on a per kg of bodyweight basis, the trend was reversed and the weight maintenance group had the highest values of EE. However, this was most likely due to the differences between groups body surface area relative to bodyweight ratio. Lastly, the bodyweight and composition maintenance groups had a lower percentage of total EE coming from sedentary activities relative to the substantial bodyweight and composition gainers.

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