Elevated levels of uremic retention solutes (URS), breakdown products of protein digestion, are associated with an increase in overall mortality, cardiovascular risk, and chronic kidney disease (CKD) progression. Increased levels of the URS Indoxyl sulfate (IS), p-cresol sulfate (PCS), and Trimethylamine N-oxide (TMAO) have been observed in patients with late stages of kidney disease (1-3). URS are formed via bacterial fermentation in the colon and are removed by urinary excretion, a task easily accomplished by healthy kidneys. However, in individuals with CKD, kidney function declines, resulting in decreased removal and subsequent accumulation of URS in the serum. However, few studies have evaluated URS in pre-dialysis CKD patients or have controlled for diet. Only one cross-sectional study evaluated levels of TMAO in both serum and urine of non-dialysis CKD patients compared with healthy adults (1), and no studies have examined all three of these URS while controlling dietary intake. Thus, in this secondary analysis, we aimed to determine serum and urine levels of IS, TMAO, and PCS in patients with moderate CKD compared with matched healthy adults who participated in a one-week controlled feeding study. Participants included patients with CKD (N=7) and healthy controls (N=7) matched for age, sex, and race. Participants consumed a diet controlled for macronutrients, fiber, phosphorus, calcium, potassium, and sodium for one week. Fasting serum and urine samples were collected at the end of the week. IS, PCS, and TMAO were quantified using LC-MS. Paired comparisons were used to determine differences between the groups and associations were examined with Pearson’s correlations. Results show that fasting serum URS were higher in CKD compared with controls (p<0.05). Urine URS tended to be higher in CKD patients, with IS reaching significance. Overall, kidney function (eGFR) was inversely related to each serum URS (p<0.05) and urine URS. However, when the relationship between eGFR and URS was evaluated within groups, strong inverse relationships only persisted in the CKD group. There were strong relationships among the serum and urine metabolites, and higher levels of serum URS corresponded with higher levels of the respective urine URS. When evaluated by group, these relationships remained strong in the CKD group, and slightly weakened in the control group. In conclusion, we have found that serum levels of URS are significantly elevated when compared with healthy adults even in early to moderate stages of CKD. Increased intestinal URS production via intestinal microbiome and altered liver function remain potential confounding variables in elevated serum URS levels over simply reduced excretion. Therapeutics, such as modified dietary protein intake or pre/pro/synbiotics, aimed at reducing URS production in the gut, may have the potential to reduce overall serum URS levels. Larger, longer studies evaluating diurnal serum URS and 24-hour urine URS excretion are needed to better understand URS retention and production in moderate chronic kidney disease patients.

<p>Obesity has ascended to become the primary modifiable cause of death in the United States. New evidence has called into question the utility of BMI – the typical index of obesity – in predicting cardiometabolic disturbances. The distribution of body fatness may be just as important as the total quantity. Intermuscular adipose tissue (IMAT) has emerged as a distinct subset of adipose in skeletal muscle that may be particularly metabolically deleterious. Typically, sections of either the calf or thigh are used as proxy measurements for whole-body IMAT in investigations. However, IMAT dispersion may not be consistent across tissues, instead infiltrating specific muscle or muscle compartments, and these have may have different metabolic consequences. The study described in Chapter 2 was designed to address this possibility and investigate and compare associations among thigh and calf IMAT stores with indices of cardiometabolic health. The strength of the relationship between IMAT and glucose control-related indices of cardiometabolic health was dependent upon anatomic location. Specifically, thigh IMAT is a better predictor of cardiometabolic risk that calf IMAT. </p> <p>Skeletal muscle has gained increased recognition in recent years for its importance in promotion of health and wellness throughout the life course. While treatment models addressing issues of declining muscle mass and strength with age previously focused on older adults, the importance of utilizing a life course model to promote skeletal muscle health at all ages was more recently recognized. There is consistent evidence that higher-protein diets modestly improve body composition. However, women are at greater risk for not meeting protein requirements and seem to be less willing to adopt strategies to achieve greater protein intake, such as protein supplementation, for fear that it may cause ‘bulkiness’. Therefore, the study described in Chapter 3 was designed to critically evaluate the effect of whey protein supplementation on body composition changes in women via a systematic review & meta-analysis of published randomized controlled trials. It was hypothesized that whey protein supplementation would moderately improve body composition but would not cause excessive muscle hypertrophy. Consistent with our hypothesis, whey protein supplementation improved body composition by modestly (<1%) increasing lean mass, without influencing fat mass.</p> <p>Dietary protein and skeletal muscle are conceptually inseparable; protein is often only considered in terms of how it impacts skeletal muscle-related outcomes. However, it is of interest to determine if the proposed beneficial effects of increased dietary protein consumption extend beyond skeletal muscle. Consumption of higher protein diets result in lower resting blood pressure, but the potential for protein to attenuate acute exercise blood pressure responses is unclear. The study described in Chapter 4 was designed to investigate the effects of meals with different amounts of protein on blood pressure responses to exercise in a randomized, cross-over trial. We hypothesized that consuming the higher-protein meal would attenuate the blood pressure responses to exercise and result in a more robust post-exercise hypotensive response. Contrary to our hypothesis, a higher-protein meal does not attenuate exercise-induced blood pressure responses compared to a lower-protein meal. These findings build upon previous research suggesting that the beneficial effect of chronically elevated protein intake on blood pressure is typically not observed in an acute setting by extending these findings to encompass blood pressure responses to acute responses to exercise.</p> <p>The three studies packaged herein utilize different techniques and report on different outcomes, but conceptual threads unite these works which augment the collective findings. Future researchers investigating the effects of protein on skeletal muscle anabolism can: 1) learn of the importance of proper reflection on surrogate measures and potential for anatomic-specific effects from the IMAT findings (Chapter 2), 2) appreciate the relevance of energy and training states in modulating responses from the WP meta-analysis (Chapter 3), and 3) recognize the importance of holistic approaches and employing challenges to reveal heterogeneity from the protein and BP trial (Chapter 4). Taken together, the research presented in this dissertation forwards our understanding of the relations and effects of dietary protein with different components of body composition on cardiometabolic health. </p>