A Systems Perspective on Mental Wellbeing and Quality of Life: Testing a Model of Dietary Behavior, Physical Condition and Inflammation on Quality of Life in a Nationally Representative Dataset

Abstract

The current dissertation tested a model based on a systems perspective, where inflammation was hypothesized to mediate the influence of diet and physical condition on quality of life (base model) in a nationally representative U.S. dataset (NHANES). Three additional hypotheses, regarding social support (The Buffering Hypothesis), early microbial exposure (The Hygiene Hypothesis) and life history theory (The Tradeoff Hypothesis) were tested utilizing the base model. All analysis utilized a structural equation model. This study focused on objective measurements for dietary behavior and physical activity utilizing blood serum values of nutrients and metabolic markers and anthropometric data as well as blood serum concentrations of CRP and white blood cell count. Quality of life was assessed with the number of limitations in daily living, the number of days that were affected by mental, emotional and physical limitations and the self-reported general health condition. The hypothesized model fit well to the data and the results revealed that lower intake of healthy nutrients and reduced physical condition both predicted decreased quality of life, as mediated by inflammation and explained 31.9 % of the variation in quality of life (R² = .319, p<.001). Social support further predicted quality of life directly (β = .417, p<.001) and indirectly through dietary behavior and inflammation (β = -.106, p<.001), microbial exposure significantly moderated the relation between inflammation and quality of life (β = -.127, p<.001) and higher reproductive effort predicted lower intake of vital nutrients (β = .316, p<.001), physical condition (β = .352, p<.001) and subsequent inflammation. Reproductive effort also directly predicted reduced quality of life (β = .278, p<.001). These analyses indicated that inflammation can be considered a strong mediator between lifestyle factors and resulting quality of life and that social support, microbial exposure and reproductive effort each added unique predictive value to this model.