Location: Obesity and Metabolism Research2019 Annual Report
Objective 1: Compare metabolic, physiologic, and behavioral responses to consumption of a high quality vs. typical American diet pattern. Sub-objective 1A. Determine if a diverse, DGA-based nutrient-rich diet elicits a superior metabolic profile in persons at-risk for metabolic disease, compared to the typical U.S. diet that strays from the DGA with respect to saturated fats, added sugars, fiber, and dairy servings. Sub-objective 1B. Determine if chronic stress, stress system responsiveness, and diet quality interact to influence metabolic health. Sub-objective 1C. Determine the effect of diet quality and physical activity level on the plasma metabolomic response to a mixed macronutrient challenge. Sub-objective 1D. Determine if combining assessment of dietary intake using the 24-h recalls, physical activity assessments, anthropomorphic measures and fasting biomarkers of hepatic lipogenesis will improve prediction of insulin sensitivity assessments over the use of fasting glucose and insulin. Objective 2: Discover interrelationships between metabolically important tissues that contribute to metabolic health and energy homeostasis. Sub-objective 2A. Characterize the gut (fecal) microbial populations in response to dietary interventions based on the Dietary Guidelines or the typical American diet, and determine how they are related to metabolic outcomes. Determine the contribution of gut microbiota to the systemic metabolome. New Sub-objectives 2B and 2C as of 1-31-2017 to reflect change in personnel expertise: Sub-objective 2B. - Identify and validate pathways that regulate plasma TMAO levels and susceptibility to cardiometabolic disease. Sub-objective 2C- Identify resident Gut Microbial Taxa that regulate plasma TMAO levels and atherosclerosis susceptibility. Objective 3: Identify physiological and psychological processes that influence behavior related to food intake. Sub-objective 3A. Link individual differences in eating behavior with metabolomics and endocrinology of hunger and satiety. Sub-objective 3B. Vulnerability and resilience to stress may be determined by metabolic responses to stress: implications for stress-eating.
We will use a multidisciplinary approach to test molecular, physiologic, and metabolic responses to diet patterns, specific nutrients, and physical activity levels to determine effects on or associations with chronic disease risks. We posit that consumption of a diet, patterned on the Dietary Guidelines for Americans (DGA), will rapidly improve cardiometabolic risk factors, improve gut barrier function and reduce metabolic dysfunction. Also, individual differences in chronic stress and stress system responsiveness will partially explain variation in metabolic responses to the DGA diet. A randomized, food-controlled trial will be conducted to test these hypotheses. We will also conduct a cross-sectional study using metabolomics to map an individual’s metabolic flexibility and link this phenotypic trait to lifestyle, including markers of health status, physical activity parameters, diet quality, food preferences and food choices. As part of this study, we will administer a meal challenge to test the hypothesis that behavioral phenotypes can be identified based on responses of known and putative satiety signals to the meal. Using the cross-sectional approach and metabolomic analyses, we will develop basal and stress-induced metabolite profiles to identify differential stress-response signatures. Ancillary studies will be conducted to examine underlying mechanisms that might explain metabolic dysfunction. To examine gut microbiota and metabolites in more depth, samples of adipose, liver, intestinal content, and blood from ‘healthy’ and ‘unhealthy’ obese undergoing gastric bypass surgery will be used to derive phenotypic signatures spanning several biological systems and adipose tissue structure/function to test the hypothesis that phenotypic signatures can predict improvement in insulin resistance and inflammation. Using a murine model of diet-induced obesity, we will test the hypothesis that obesity disrupts the normal association between peripheral nervous system (PNS) sensing of ambient temperature and communication to the brain to coordinate temperature-control of feeding and energy expenditure. This study will include functional tests in vivo, and PNS expression of temperature-sensing TRP channels will be evaluated in dorsal root ganglion ex vivo. Finally, cultured muscle cells will be used to examine the hypothesis that incomplete mitochondrial combustion of fatty acids in tissue such as muscle leads to increased acylcarnitine accumulation, and select acylcarnitines promote cell stress responses will be evaluated.
This is the final report for project 2032-51530-022-00D, which expired March 2019, and continues under new project 2032-51530-025-00D. Objective 1 contained two important studies: 1) a human intervention comparing metabolic outcomes in response to a typical American diet (TAD) pattern and a diet pattern based on the Dietary Guidelines for Americans (DGA); 2) an observational study of healthy adults. These studies were designed to investigate variance in human metabolism relating to dietary intervention or habitual dietary intake. The intervention study comparing a DGA diet pattern and a TAD pattern served as the foundation for Sub objectives 1A, 1B, and 2A. Fifty-two overweight women with glucose intolerance or elevated blood lipids participated in this study. The trial was completed in 2017. Partial support was provided by subordinate project 2032-51530-002-20T with Dairy Research Institute, "Evaluation of Health Benefits of a High-quality Diet in Persons At-risk for Development of Metabolic Disease: Rapidity & Weight-independent Effects." The first manuscript, published in August 2018, reported decreased systolic blood pressure after eating the DGA diet, but no effect of the DGA intervention on glucose tolerance. Outreach activities were done to familiarize professionals and consumers about this study at the California Academy of Nutrition and Dietetics and the California Area Indian Health Service. Sub-objective 2A focused on the intersection of stress, cognitive behavior, and how these might be influenced by dietary interventions. A manuscript was published in November 2018; results indicated that the inclusion of more vegetables and less sodium (as recommended by the DGA) mediates the stress load of eating a controlled diet. In a secondary analysis, self-reported feelings of stress were lower after exposure to the DGA diet, but this was only observed in subjects whose intake of omega-3 fatty acids increased compared to their pre-study intake. Initial analyses of cognitive behavior indicated that reaction time improved in response to the DGA diet. In conjunction with Sub-objectives 1A and 1B, the aim of Sub-objective 2A was to analyze the resident gut microbial community using fecal samples collected during the DGA intervention study and relate these findings to the participants’ responses to the diet intervention and to the challenge meal. Metabolites derived from the human ‘host’ and those derived from the resident microbial community living in the gut were included in the analysis. Samples for microbiota analysis were completed by our ARS collaborator in Little Rock, Arkansas. Preliminary results, presented at a national meeting in 2019, indicated that eating the DGA diet pattern produced few differences in the fecal microbiota compared to the TAD. Several additional publications are in preparation to complete the research outlined in Sub-objectives 1A and 1B. A manuscript describing the challenges of planning, implementing, and monitoring adherence to menus for a controlled feeding trial has been submitted for review. Other manuscripts are being prepared to address the effect of the DGA diet on cognitive function, immunological function, and metabolic and blood lipid responses to a defined nutritional challenge provided as a high-fat test meal; a prevailing theme in these papers is to identify the degree of variation in individual responses as a step toward individualized nutrition recommendations. The observational study was designed to investigate variability in human metabolism between men and women, across a range of age (18 to 65 years) and body fatness (body mass index of 18.5 to 39.9, the ratio of weight in kilograms to height in meters squared). The study commenced in June 2015, and enrollment of the proposed 396 participants was nearly completed by the end of this project cycle. The observational study served as the foundation for Sub-objectives 1C, 1D, and 3A in this project plan. A peer-reviewed manuscript describing the study design and protocols was published in 2017. The aim of Sub-objectives 1C and 1D was to measure how individuals respond to a defined nutritional challenge providing a foundation for “nutritional phenotyping.” To support this effort, new analytical techniques were developed by ARS scientists and their collaborators at the University of California Davis to efficiently assess broad swaths of metabolites in blood, urine, and fecal samples. These methods and commercially available analytical products were applied to provide profiles of metabolites and hormones for each participant in response to the challenge meal. These data were paired with the established method of indirect calorimetry to measure energy and fuel use by the body to round out the phenotypic dataset. Several manuscripts are in progress to identify predictive models of insulin sensitivity, to understand factors that contribute to postprandial lipid clearance and switching between the use of glucose and fat fuels as main source of energy production. The aim of Sub-objective 2B was to identify and validate pathways that regulate plasma trimethylamine N-oxide (TMAO) levels and susceptibility to cardiovascular disease. TMAO is a microbial byproduct of choline metabolism that is processed by the liver, excreted into the general circulation, and has been associated with the formation of atherosclerotic lesions and cardiovascular disease risk. Targeted methods were developed and used to analyze samples from the DGA intervention study. There were no differences in circulating TMAO between the diet intervention groups. The results have been published in abstract form, and manuscripts are in preparation. Additionally, collaborative studies conducted with animal models have identified hepatic expression of micro interfering RNA (miR)-146 and the genes Numb and Dlst on Chromosome 12 form a genetic pathway that influences plasma TMAO levels. A peer-reviewed manuscript describing these results was published (July 2018), and results have been presented at a Keystone Conference and a FASEB Conference. To determine if there are microbes in the gut that regulate plasma TMAO levels and susceptibility to atherosclerosis (Sub-objective 2C), samples were collected from mice derived from breeding male mice with genes making them susceptible to atherosclerosis [apolipoprotein E-Leiden (ApoE*3Leiden) and cholesterol ester transfer protein (CETP)] and female mice with a diversity of genes (the Diversity Outbred (DO) mice). The offspring (262 female; 269 male) of this cross-breeding (DO-F1) were examined for over 20 cardio-metabolic traits after eating a high fat/cholesterol (HFHC) diet for 12 weeks. The traits included atherosclerotic lesion size, blood pressure, bone mass, and plasma alanine aminotransferase (ALT; a test of liver function), total cholesterol (TC), triglyceride (TG), and glucose. We observed some differences between sexes in these traits. For example, compared to males, female mice had larger atherosclerotic lesion areas (339 percent higher) and greater hyperlipidemia (TC 71 percent higher; TG 20 percent higher). Adiposity and circulating levels of glucose were also different with male mice having greater plasma glucose levels (12 percent higher), body fat percentage (14 percent higher) and bone mass (p < 0.001, 5 percent higher) than female mice. We also observed a significant effect of the HFHC diet on plasma atherosclerotic risk factors including: increased plasma ALT, TC, and bone mass; decreased plasma glucose and TG. Subsequent analyses will focus on genetic regulation of these traits with a focus on interactions between diet and genes. The aim of Sub-objective 3A was to develop a comprehensive model of satiety using data generated in the observational study. Partial support for this work came from subordinate project 58-2032-6-010-F with Arla Foods. The model focuses on satiety and hunger signals generated by peripheral tissues that provide input to feeding centers in the brain. An example is the endocannabinoid system (ECS), a neurometabolic system that acts in the brain. The link between this system and appetite was explored in a subordinate project conducted by ARS scientists in Davis, California, and collaborators at the Indiana School of Medicine and the University of Connecticut Health Center. In a sample of elderly women and men, different endocannabinoids had different associations with appetite: the eighteen carbon fatty acid ethanolamides increased appetite, while the long-chain omega-3 fatty acid ethanolamide decreased appetite. In a study of craving in healthy young women, oleoylethanolamide was inversely related to craving sweet-rich foods but positively related to craving carbohydrates. These studies show that measuring the complete endocannabinoid profile provides information that improves our understanding of how these compounds influence eating, cravings, and appetite regulation. The laboratory analysis of endocannabinoids and other hormones linked to appetite in samples generated during the observational study is in progress and will be used to fulfill Sub-objective 3A. To understand how stress responsiveness relates to dietary intake (Sub-objective 3B), progress was made by completing cortisol analyses, cognitive, physiological, and self-report data on the first 50 subjects who completed the observational study. In consideration of how knowledge about stress responsiveness may improve strategies for dietary interventions, a talk that focused on interrelationships between stress responsiveness, the decision-making brain, and dietary flexibility was presented at a national meeting. A model was presented for demonstrating the power in embracing and understanding variability as it potentially applies to refining intervention strategies and interpreting intervention outcomes.
1. High quality diets and stress. Very little is known about how whole food diets, such as those based on the Dietary Guidelines for Americans (DGA), influence psychological stress and physiological stress load. To better understand the effects of whole food diets on stress, ARS scientists in Davis, California, examined in a randomized control trial the effects of a DGA-based diet on markers of psychological and physiological stress. Results suggested that adopting and adhering to a diet of higher quality (DGA) for eight weeks may have been generally more psychologically and physiologically stressful if consumption of this whole food DGA based diet did not also include improvements in vegetable or sodium consumption, relative to the participant’s typical diet prior to the intervention. This study, which was published in the journal Nutrients and selected as a “Feature” article, provides further evidence for the mental health benefits of maximizing vegetable and minimizing sodium consumption, both of which may prevent induction of psychological and physiological stress in persons trying to adopt and adhere to a heathier diet.
2. Association between plasma LDL cholesterol and microRNAs in the liver. MicroRNAs (miRNAs) have emerged as genetic fragments that are important regulators of metabolism, have been implicated in affecting circulating levels of lipids known to increase risk of atherosclerosis, and have been shown to respond to dietary changes. ARS scientists in Davis, California, implemented a systems genetics strategy using the Diversity Outbred (DO) mouse population to study diet and miRNA. Gene and miRNA expression profiling in the livers from approximately 300 genetically distinct DO mice after 18 week on either a high-fat/high-cholesterol diet or a high-protein diet revealed a co-regulated module of miRNAs significantly associated with circulating low-density lipoprotein cholesterol (LDL-C) levels. This work demonstrates that a high-fat/high-cholesterol diet robustly rewires the miRNA regulatory network, and researchers have identified a small group of co-regulated miRNAs that may exert coordinated effects to control circulating LDL-C.
3. Improving metabolic health through precision dietetics in mice. ARS scientists in Davis, California, investigated how genetic differences influence health responses to several popular diets in mice. These diets are similar popular diets that are representative of those eaten by historical human populations. Utilizing mice allows for precise genetic and environmental control. Across four genetically distinct inbred mouse strains, the researchers compared the American diet's impact on metabolic health to three alternative diets (Mediterranean, Japanese, and Maasai/ketogenic). Critically, health effects of the diets were highly dependent on genetic background, demonstrating that individualized diet strategies improve health outcomes in mice. If similar genetic-dependent diet responses exist in humans, then a personalized, or "precision dietetics," approach to dietary recommendations may yield better health outcomes than the traditional one-size-fits-all approach.
4. Circulating lipoproteins transport important compounds that are functionally significant. Lipid transport in the blood within lipoprotein particles has been primarily considered for its energy delivery and cholesterol removal properties, but these lipid laden particles also contain bioactive lipids that can modify the physiological responses of tissues. ARS scientists in Davis, California, in collaboration with scientists at the University of California, Davis, and the Pennsylvania State University, conducted studies to investigate how diet alters lipoprotein particle bioactive lipid composition, and how particle composition was either associated with atherosclerotic risk factors or influenced cellular inflammatory responses. They discovered that: 1) lipoprotein particles enriched in certain oxygenated lipids caused endothelial cells in culture to increase the expression of proteins that allow white blood cells to stick, an event thought to initiate atherosclerosis; and 2) walnut consumption increased particle anti-inflammatory lipids that reduced diabetic fat cell responses to inflammatory stimuli. These findings demonstrate that diet can modulate the bioactive lipid composition of lipoprotein particles, which in turn can modulate peripheral tissue inflammatory responses associated with positive health outcome.
5. Sweat is a valuable matrix for skin research. Secretions of specific tissues often hold clues about the metabolic health of those tissues, and/or insights into diseases which disrupt those systems. Sweat is one of the primary secretions of the skin, and understanding the chemical content of sweat and factors which influence it may provide novel insights into skin biology to allow maintenance of optimum skin health. ARS scientists in Davis, California, conducted a series of studies in collaboration with colleagues from the University of California, Davis, and California State University, Sacramento, to develop and characterize sweat collection and perform analyses for the determination of lipids and lipid mediators of inflammation in this biological fluid. During the course of these studies they determined that 1) the lipid composition of sweat does not change during the day or at different collection sites, but is influenced by how the sweat is collected; 2) an inflamed skin condition called eczema influences lipid mediators in sweat collected in the absence of active lesions, pointing to a subtle underlying metabolic defect in this disorder; and 3) oral ibuprofen has different effects on plasma and sweat lipid mediator profiles, supporting the hypothesis that the lipids in sweat are produced in the skin and not collected from the blood stream. These findings provide a novel set of well characterized tools for researchers to investigate skin health.
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