Objective 1: Determine the effect of consuming dietary sources of fat with varied saturation and chain length on the physiological responses of satiety, lipid oxidation, and energy metabolism. Sub-objective 1A: Determine the acute effects of consuming dietary fats of varied saturation and chain length on satiety, thermogenesis and energy utilization in healthy individuals. Sub-objective 1B: Determine the chronic effects of consuming dietary fats of varied saturation and chain length on satiety, energy utilization, and body composition. Objective 2: Determine the role of long chain omega 3 (LCn3) fatty acids in modulating the function of bone cells and the contribution of RANKL/RANK/OPG pathway in obesity-induced changes in bone metabolism in animal and cell models. Sub-objective 2A1: Define the role of LCn3 in preventing adiposity-induced bone loss. Sub-objective 2B: Define the optimal ratio of n6/n3 in improving bone quality and quantity in an obesity animal model. Objective 3: Define the influences of dietary fatty acids and energy balance upon conversion of alpha-linolenic acid (ALA; 18:3n3) to LCn3. Sub-Objective 3A: Determine the effects of saturated fatty acids (SFA) content upon mechanisms of ALA disposition under eucaloric conditions. Sub-Objective 3B: Determine the effects of SFA content upon mechanisms of ALA disposition in rodents under hypercaloric conditions. Objective 4: Define the extent to which consuming rainbow trout bred for elevated LCn3 content reduces CVD risk markers, such as platelet reactivity and related eicosanoids, in people.
Fat is an essential part of a healthy diet. However, the fatty acid compositions of dietary fats are often overlooked in designing healthy diets. Many Americans consume diets high in saturated fatty acids (SFA) and low in unsaturated fatty acids, including long-chain omega-3 fatty acids (LCn3). This imbalance may contribute to obesity and exacerbate osteoporosis and cardiovascular disease (CVD). The aim of our work is to provide robust data that will inform evidence-based recommendations for the appropriate levels and composition of dietary fats to maintain health and prevent disease. We will accomplish this aim by completing four research objectives that will clarify how the fatty acid profile of dietary fat contributes to health, or conversely, to disease progression. These objectives will use a combination of clinical translational studies in humans and mechanistic studies in rodents and isolated cells. Objective 1 addresses the role of dietary fats in the development of obesity by studying their effects on the modulation of satiety and energy metabolism; Objective 2 addresses the roles of specific fatty acids in preventing bone structure deterioration and promoting bone health in obesity; Objective 3 addresses the impacts of dietary fatty acids and energy balance on LCn3 metabolism; Objective 4 addresses the impact of consuming LCn3-rich rainbow trout on CVD risk markers in humans. We will fulfill these objectives through a combination of clinical translational and mechanistic studies involving human volunteers and rodent models.
This is the final report for the project 3062-51000-053-00D entitled “Food Factors to Prevent Obesity and Related Diseases” that will terminate September 30, 2019. The project focused on the influence of dietary fats and oils to reduce obesity and its key associated problems of cardiovascular disease (CVD), fatty liver, insulin resistance, and bone loss. This project included a cross-program, “farm to fork” collaboration to improve the content of heart healthy omega-3 polyunsaturated fatty acids in farmed rainbow trout. Substantial results were made over the five years of the project. The goal of Objective 1A was to evaluate the acute energetic and satiety responses to dietary fat intake in humans in order to shed light on whether some dietary fats may be helpful to prevent obesity. Specifically, the responses to saturated fat, monounsaturated fat, and polyunsaturated fat, or long chain omega-3 fatty acids were evaluated. Other highlights of this objective are studies demonstrating the positive health impact of eating farmed salmon upon lipoproteins (risk factors for CVD) in humans and collaborative projects that identify demographic relationships to fish intake in Americans and modeling the impact of high-oleic acid oil intakes upon fatty acid intakes in the American population. These data will be useful for nutritionists and agricultural/aquacultural producers. The studies in Objective 2 investigated the impact of polyunsaturated fatty acids upon bone health in obese animals. The data from these studies indicate that lowering the ratio of omega-6 and omega-3 polyunsaturated fatty acids (linoleic acid vs alpha-linolenic acid) does prevent obesity-induced bone loss in mice. On the other hand, supplementing diets with fish oil containing long chain omega-3 polyunsaturated fatty acids did prevent obesity and bone loss in mice. An ancillary project demonstrated that increased consumption of fruits and vegetables at or above federal dietary guidance improves bone health in humans. Mechanistic experiments determined that loss of bone-marrow adipocytes increased the number of bone-forming osteoblasts in obese mice. The data from this work provide mechanistic and clinical insight into how diet through intake of fats, oils, fruits and vegetables can improve bone health. The studies in Objective 3 examined the impact of saturated and monounsaturated fats upon the ability of mice to convert dietary polyunsaturated fatty acids like alpha-linolenic acid and linoleic acid to their bioactive long chain polyunsaturated fatty acids. Our data demonstrate that intake of the high-fat, obesogenic diets increased the amounts of long chain polyunsaturated fatty acids in several tissues but that diets high in oleic acid increased fatty liver and insulin resistance. Following up on these studies, we showed that medium chain saturated fatty acids as part of a high-fat, high energy diet, while still inducing weight gain in mice, increase the tissue content of long chain polyunsaturated fatty acids without causing fatty liver or insulin resistance. Current studies take advantage of the upcoming Unit projects and are determining if time-restricted feeding or addition of fermentable fiber to high-fat diets can result in elevated long chain polyunsaturated fatty acids in tissues while preventing the obesity-induced outcomes of fatty liver and insulin resistance. We developed a novel means of characterizing and analyzing lipidomic biomarkers of fatty acid nutrition in human plasma using an infusion-based, mass spectrometric approach. This novel method allowed us to determine that omega-3 polyunsaturated fatty acids in human plasma are incorporated into selective phospholipid and triacylglycerol lipid molecules following intake of farmed salmon. Efforts to streamline the sample handling and data processing have been successful. These technological advancements will assist clinical and basic scientists in improving biomarker analysis for human nutrition and disease outcomes. This research led to the formation of an international collaboration with Canadian scientists to understand how a person’s genetic background may affect these lipidomic biomarkers. Given the expertise in lipid analysis and population modeling of lipid intakes developed as part of Objective 1 and Objective 3 of this project, scientists at Grand Forks, North Dakota, were invited to play an integral role in two of the Agency sponsored Grand Challenge projects “Dairy Agriculture for People and the Planet” and the “Beef Grand Challenge”. The work for the “Dairy” Grand Challenge required the analysis of several hundred fluid milk samples in order to determine the impact of forage type upon the lipid quality of milk. Analysis of these results is ongoing. We are currently completing a modeling study to examine whether saturated fat intake by Americans can be lowered by changing the forage for or breeds of cattle. These results will have impact for beef producers, nutritionists, and the American population. In the clinical trial as part of Objective 4, we are comparing the efficacy of fish with differing long chain omega-3 fatty acid contents to reduce CVD risk markers in obese people with elevated CVD risk. The work is a collaboration with the National Center for Cool and Cold Water Aquaculture in Kearneysville, West Virginia. The trial is ongoing. As part of this collaboration we examined means to increase long chain omega-3 fatty acid content in rainbow trout while reducing fish meal feedstock input. Our data indicate that fatty acids accumulate during aging in triploid female trout unable to undergo sexual maturation vs diploid trout. We also demonstrated that fasting prior to providing the finishing diet does not improve tissue accumulation of long chain omega-3 fatty acids in fillets and that feeding rainbow trout a finishing diet enriched with long chain omega-3 fatty acids increases the omega 3 fatty acid content of trout fillets in a fillet-dependent manner. These findings will benefit fish producers by determining optimum finishing strategies and American consumers that wish to consume foods with an elevated content of long chain omega 3 fatty acids. The results regarding lipid metabolism and the technologies derived from this project were used for the successful development and transitioning to the replacing project 3062-51000-055-00D “Food Factors, Meal Patterns, and Lipoproteins” that begins October 1, 2019.
1. Medium chain saturated fats reduce obesity severity in mice. Dietary fats comprise 30% of average daily energy intake. Overeating saturated fat is associated with elevated obesity, fatty liver, inflammation, and insulin resistance. Medium chain saturated fats, also known as medium chain triglycerides (MCTs), are metabolized differently than other fats and are found in coconut oil and palm kernel oil of which over 11.5 million metric tons are produced annually. ARS scientists at Grand Forks, North Dakota, studied whether substituting medium chain saturated fats for long chain saturated fats would reduce obesity outcomes in mice. Using carefully formulated diets, the research showed that obese mice eating the medium chain saturated fats had reduced insulin resistance, fatty liver, and inflammation compared to mice that ate the long chain saturated fats. These data suggest that medium chain saturated fats may provide benefit for reducing obesity outcomes and warrant subsequent clinical study.
2. Dietary omega 3 fatty acids regulate specific genes in the growing brain. Dietary omega-3 polyunsaturated fatty acids are essential for cognitive development, but most research only has focused on antenatal and postnatal time periods. Omega 3 fatty acids are found in cold water fish like salmon and trout as well as in oils like flaxseed oil, canola oil, and soybean oil. While the brain is still developing in late childhood and adolescence, and the impacts of dietary omega-3 fatty acids during this critical period are not known. ARS scientists at Grand Forks, North Dakota, studied the cerebellum, a part of the brain that regulates movement coordination and develops into adolescence. In these studies, healthy young rats (similar in age to 2-3 year old humans) were given diets with trace amounts of omega-3 fatty acids. Researchers found that even at age 7 weeks (similar in age to an adolescent human) on the omega-3 depleted diet, expression of genes, particularly the gene Nr4a3, in the cerebellum changed although there was minimal loss of omega-3 in the cerebellum itself. These data shed light on an under-addressed area of fatty acid nutrition, demonstrate a potential new biomarker of omega-3 fatty acid intake, and are important for nutrition scientists who study the long-term development of the nervous system in undernourished children and adolescents.
3. Dietary omega-6 fatty acids, obesity, and bone health. Bone weakening is now being recognized as a consequence of obesity, and data suggest that inflammation plays a major role in this process. One school of thought suggests that too much dietary omega-6 fatty acid (such as found in corn oil or soybean oil) may cause inflammation and obesity. ARS scientists at Grand Forks, North Dakota, investigated whether changing the amount of omega-6 fatty acids modified bone health and obesity in mice. Results from this study demonstrated that neither obesity nor bone structure was affected by the amount of omega-6 fatty acid in the diet and do not support the claim that dietary omega-6 fatty acids (as found in commodity soybean oil and corn oil) are a cause of obesity. These data will be useful for nutrition scientists and other biomedical scientists studying the causes and prevention of obesity and bone loss.
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