Location: Obesity and Metabolism Research2016 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. Sub-objective 2B. Characterize metabolic phenotypes and alterations in physiological network cross-talk that correspond to unhealthy and healthy overweight/obesity states. Sub-objective 2C. Investigate the causes of inflammation and cellular stress responses that are associated with obesity, insulin resistance and metabolic syndrome: the roles of specific metabolites and perturbations in metabolic pathways. 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.
Progress was made on all three objectives, which fall under National Program 107, Component 3: Scientific Basis for Dietary Guidance and Component 4: Prevention of Obesity and Obesity-Related Diseases. Progress focuses on the conduct of two important human trials that were designed to address the variability in human metabolism as it relates to dietary intervention or to habitual dietary intake. A randomized controlled trial to examine the health benefits of a diet pattern based on the Dietary Guidelines for Americans continued this year. The target sample is females at risk for metabolic disease. In this second year of the project, a total of 41 participants have enrolled with the goal of enrolling 60 participants over the four-year project. The intervention study serves as the foundation for sub-objectives 1A, 1B, and 2A. Partial support for this study is coming from subordinate project 2032-51530-022-20T with Dairy Research Institute. A method was developed for estimating dietary compliance that provides investigators with a rapid assessment of participant adherence to study foods and addition of non-study foods, beverages, or condiments. A cross-sectional phenotyping study is now in its second year and has enrolled approximately 119 subjects out of a total of 400 participants needed over the course of the four-year project. Of those enrolled, 97 have completed the study and nine are in progress. The phenotyping study serves as the foundation for sub-objectives 1C, 1D, and 3A. Partial support for sub-objective 3A is coming from subordinate project 58-2032-6-010-F with Arla Foods. Preliminary results combining whole body energetics with metabolic regulators of energy metabolism were presented at an international meeting. In partial fulfillment of sub-objectives 1C and 1D, a paper describing the design and protocols of the phenotyping study has been prepared and submitted for publication. In addition, a demonstration of the phenotyping approach using a nutritional challenge was recently reported. Our preliminary results show that individual people can have widely variable responses to the same nutritional challenge, putting into question some of our basic assumptions underlying dietary recommendations to promote public health. Measuring how individuals respond to a defined nutritional challenge provides a foundation for nutritional phenotyping, and new analytical techniques that measure broad swaths of metabolites simultaneously offer high resolution images of these response phenotypes. ARS scientists in Davis, California, and their collaborators at the University of California Davis, used this combination of a nutritional challenge and analysis of metabolites to assess individual variation in the metabolism of the rare dietary fatty acid, gamma linolenic acid. While all subjects absorbed the dose of this fatty acid, and it became incorporated into an array of complex lipids, only five of the seven subjects were able to convert this fatty acid into its product within eight hours, suggesting that the enzyme involved in this conversion differs between some individuals. This study is important because it provides clear evidence that individual differences in enzymatic capacity can modulate the nutritional and metabolic phenotype of a person, which may, in turn, modify dietary requirements for optimal health. The endocannabinoid system (ECS) is a neurometabolic system that acts in the brain that may be an important appetite regulator that is being studied in sub-objective 3A. The link between this system and appetite was explored in a subordinate project conducted jointly by ARS scientists in Davis, California, and collaborators at the Indiana School of Medicine and the Center on Aging, University of Connecticut Health Center. The association between blood levels of endocannabinoid compounds and self-reported appetite and satiety were analyzed in a sample of elderly women and men. Different endocannabinoid compounds had different associations with appetite: the eighteen carbon fatty ethanolamides increased appetite, while the long-chain omega-3 fatty ethanolamide decreased appetite. This study demonstrated that it is important to measure the complete endocannabinoid profile to understand how these compounds influence appetite regulation. To understand how stress responsiveness is related 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 phenotyping study. In addition, a consideration of how knowledge about stress responsiveness may improve strategies for dietary interventions, a talk was presented at a national meeting that focused on interrelationships between stress responsiveness, the decision-making brain, and dietary flexibility. 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. For agreement 58-5306-03-037F, with the University of Copenhagen, Denmark, profiles of oxylipins and global metabolomics were quantified in two strains of mice on high fat diets with variable durations of cold stress. The cold sensitive strain had a dramatic upregulation of adipocyte cyclooxygenase activity, whereas cold exposure induced soluble epoxide hydrolase activity in both strains. We also discovered that specific metabolite classes showed gender-specific exaggerations. Results have been transmitted to the collaborator, and manuscript preparation is in progress. In a second study, humans with high and low levels of intrascapular brown fat were identified and metabolite profiles were performed on brown and white fat biopsies. Discrete metabolic patterns were found between brown vs. white adipose. Both white and brown fat from subjects with low brown fat had distinct metabolic patterns when compared to these fat samples of their high brown fat counterparts. Collection and incorporation of additional gene expression data are underway and will be combined with these results for manuscript preparation. Identifying factors leading to variability in phenotypic responses in tissue and plasma metabolomes are fundamental questions within the parent project which are enriched by this subordinate project. For agreements 58-5306-4-050F and 58-5306-4-043F, with the Captain Vasillis Foundation and GAEA Products S.A. respectively, which are 50/50 co-funders of a pilot project titled “Impact of Extra Virgin Olive Oil Oleocanthal Content on Platelet Reactivity in Healthy Humans” extra virgin olive oils (EVOO) from different olive cultivars were identified by their oleocanthal, oleacien, and total phenolic concentrations. Four oils were selected with either a high oleocanthal to oleacein ratio, a low oleocanthal to oleocien, or with low oleocanthal and oleacin, but equivalent total phenolics. Subjects (n=9) completed the four week protocol and a potentially beneficial reduction in platelet reactivity was observed in 60% of subjects consuming oleocanthal-rich oils through a cyclooxygenase-independent mechanism. Untargeted metabolomic profiling indicated dietary factors including habitual intake of soy and possibly olive products influenced the anti-platelet aggregation response to oleocanthal-rich EVOO consumption. This work has been presented at international meetings in Spain and Greece, and a manuscript describing the findings will be submitted shortly. Understanding variability in human phenotypic responses to diets and dietary components are fundamental questions within the parent project enriched by this subordinate project. For log# 0047113, with University of California Davis, the Lipid Mediators Advancement Core was formed as a subcomponent of the West Coast Central Comprehensive Metabolomics Research Center (WCMC), and is housed at the Western Human Nutrition Research Center (WHNRC). To support research into whole grain impacts on energy metabolism and gut microbiota, USDA researchers validated mass spectrometry-based quantitative short chain fatty acid analyses with robust quality assurance protocols. The methods have been used to study the impact of genetic manipulation of wheat to enhance butyrate production by gut microbes after consumption. Butyrate improves insulin sensitivity and increases energy expenditure. The validation of this approach for human plasma sample analysis is underway, but will be critical for translational research objectives exploring whole grain consumption and glucose control. In collaboration with WCMC staff, novel 96-well plate sample preparation methods are under development that will allow the quantification of a broader spectrum of low abundance lipid mediators in a single analytical run. Further activities included efforts with collaborative research partners that will enhance and inform interpretation of phenotypic changes within a nutritional context (Objective 1) and support the discovery of cross-talk between metabolically active tissues (Objective 2). As examples, ARS provided advanced analytical chemistry support to optimize pre-analytical sample handling for improving quality of metabolomics data, and metabolomic analyses for studies on zinc status and plasma triglycerides, omega-3 fatty acid feeding and endocannabinoid profiles, vitamin A status and plasma signaling lipids and bile acids, endocannabinoid-dependent modulation of inflammatory regulation and mediator profiles in cell culture, obesity and plasma lipid markers of hepatic lipid health. All methods developed in this reporting year were fundamental advancements which will support the phenotyping goals within the current parent project.
1. Factors identified that are associated with following the Dietary Guidelines for Americans. Adherence to the Dietary Guidelines for Americans (DGA) is poor, and the DGA Advisory Committee recommended more studies to determine factors that promote (“facilitators”) and those that impair (“barriers”) adherence, particularly among special populations. Moreover, there are limited studies examining whether barriers and facilitators of DGA adherence explain high rates of obesity. An ARS multi-site community study, titled HEALTH, was conducted to address this understudied question in fifth grade children and adults. An ARS scientist in Davis, California represented the western region in this multi-site study. Findings from this study are among the first to show that more barriers to DGA adherence were associated with higher body mass index (BMI), an index of obesity. This information can be used by health professionals to design educational and intervention programs aimed at improving DGA adherence and reducing the prevalence of overweight and obesity in the United States.
2. Vitamin C and vitamin E affect lipid profiles in insulin resistant, obesity-prone rats. Scientists have theorized that when the liver does not respond well to insulin, as often occurs in obesity, this may be caused by lipids that are known to cause inflammation; therefore anti-oxidants that block formation of these lipids could reduce the incidence of insulin resistance. ARS scientists in Grand Forks, North Dakota and Davis, California collaborated to assess the impact of the dietary anti-oxidants (vitamin C and vitamin E) on the progression of insulin resistance and liver lipid profiles in obesity-prone rats. Anti-oxidants reduced the formation of inflammatory lipid formation but did not block the development of insulin resistance. On the other hand, obesity increased the accumulation of lipid markers of unhealthy accumulation of fat in the liver, and these were unaffected by anti-oxidant therapy. This study demonstrates that the obesity-associated changes in the liver’s ability to regulate glucose and lipid metabolism are independent of the obesity-associated liver inflammation which occurs in this animal model of obesity.
3. Both morning and evening diet choices affect diet quality. Eating breakfast is known to improve diet quality, but little is known about how diet choices at subsequent meals or snacks relates to diet quality. ARS scientists at Davis, California, examined diet quality of women who ate breakfast regularly and those who did not, focusing on the type of food choices made later in the day. Results confirmed that the women who ate breakfast had better diet quality scores determined by the Healthy Eating Index-2010 scores, an index tied to how well the diet complies with the Dietary Guidelines for Americans. The lower diet quality scores of the women who usually skipped breakfast were attributed to less consumption of fruits and whole grains overall, and higher levels of sugar, saturated fat and empty calories in their evening food choices. Poor evening food choices and low diet quality scores for the breakfast skippers were accentuated in the women who reported highest levels of chronic stress, whereas a relationship between chronic stress and diet quality was not seen in the breakfast eaters. This study provides the most comprehensive assessment of diet quality related to time-of-day eating, and shows that, for the first time in humans, eating a meal in the morning may buffer stress eating.
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Cajka, T., Davis, R., Austin, K.J., Newman, J.W., German, J., Fiehn, O., Smilowitz, J.T. 2016. Using a lipidomics approach for nutritional phenotyping in response to a test meal containing gamma-linolenic acid. Journal of Proteome Research. 12:127. doi: 10.1007/s11306-016-1075-9.