Location: Food Components and Health Laboratory2015 Annual Report
Diet is a modifiable factor that can influence the multitude of chronic health disorders that face the U.S. adult population, including type 2 diabetes, cardiovascular disease, some cancers, arthritis, endothelial dysfunction, and others. Through the experiments planned for this project, we will attempt to improve the understanding of the influence of diet on chronic disease. We will investigate direct effects of diet on cardiometabolic profile and additionally factors that influence weight gain, which increases risk for chronic disease. Objective 1. Determine the energy content of specific foods in the context of a mixed diet, and the absorption, metabolism and impact on biomarkers for health promotion of these foods or their macro and micro components. Objective 2. Determine the influence and interaction of the composition of food intake and exercise on glucoregulation, cardiometabolic profile, and metabolic flexibility (fuel management). Objective 3. Determine the extent to which the day-to-day variation in daily voluntary food intake, measured over at least 3 months, is related to diet composition, physical activity, and changes in physiological and metabolic markers related to energy balance, satiety and hunger.
Diet is a modifiable lifestyle factor that can influence the multitude of chronic diseases faced by an increasing proportion of the U.S. population, including type 2 diabetes, hypertension, vascular dysfunction, cardiovascular disease, cancer, and arthritis. Moreover, the widespread global prevalence of these diseases threatens the quality of life and places additional stresses on an already overburdened health care system. This project, through highly controlled human feeding studies, will target specific factors which influence risk for and development of chronic disease. First, research will be conducted to improve accuracy of the energy value of foods, which can impact weight gain, a risk factor for chronic disease. Second, research will be conducted to investigate dietary factors that can influence cardiometabolic profile, i.e. risk for cardiovascular disease, stroke, or diabetes. Third, we will study how diet influences voluntary food intake, again impacting weight gain, a risk factor for chronic disease. The outcomes of this research will provide a better understanding of 1) the energy content of specific foods in the context of a mixed diet, and the absorption, metabolism and impact on biomarkers for health promotion of these foods or their components, 2) dietary and lifestyle influences on diabetes and cardiovascular disease risk, and 3) the extent to which the day-to-day variation in daily voluntary food intake is related to diet composition. This research will fill knowledge gaps in the metabolism of macro and micro food components related to the development and management of obesity and chronic diseases, and provide a scientific basis for dietary recommendations and nutrition policy.
Progress was made for two objectives of this project plan linked to National Program 107 plan, focusing on Component 3 to provide a Scientific Basis for Dietary Guidance. Progress has been made addressing Problem Statement 3B: Identify Roles of Food, Food Components and Physical Activity in Promoting Health and Preventing Disease through studies on tree nuts and energy metabolism. Building on previous research, additional studies were conducted to measure the metabolizable energy of tree nuts, which previous studies have shown are difficult to digest. To accomplish the plan’s objective 1 (determine the energy content of specific foods in the context of a mixed diet) this research was conducted to evaluate the accuracy of Atwater factors that are typically used in determining the metabolizable energy value (which is the value listed on the food label) of foods. The Atwater factors were developed in the early 1900s and meant to be used for complete diets and not individual foods. However, despite their intended use for generalized diets, they have been used for labeling of individual foods and their accuracy for individual foods has seldom (perhaps never) been evaluated. A study of walnuts was initiated and completed. Similar to previous work, the Atwater approach for calculating the energy content of walnuts overestimates the actual calories by 21%. Also building on previous research with almonds, a second study of almonds was conducted to determine how the physical form of almonds affects their metabolizable energy value. A clinical intervention was completed with the objective of this project to measure, in humans, the metabolizable energy value of four forms of almonds when consumed as part of a complete diet. The almond forms were 1) whole raw, 2) whole roasted, 3) chopped, and 4) butter. The energy value of whole raw almonds was greater than that of roasted whole almonds. There was no difference between roasted whole and chopped; however, both whole roasted and chopped had a significantly lower ME value compared to butter. Atwater factors (general or specific) provide inaccurate estimates of ME for almonds whether they are consumed whole, whole roasted, or chopped, whereas they are accurate for butter. It is likely that estimates of macronutrient digestibility used to develop the Atwater general and specific factors are incorrect for nuts. Research continues investigating dietary plant sterols (objective 1, determine the absorption, metabolism and impact on biomarkers for health promotion of foods or their macro and micro components). Dietary plant sterols can reduce LDL cholesterol in people by 10 to 20%, mostly through decreasing cholesterol absorption. There is significant variation among people in their response to consumption of dietary plant sterols. A randomized clinical trial was conducted to investigate whether the change in cholesterol absorption in response to plant sterol consumption was related to the change in circulating LDL-C concentrations in individuals with a high or low ability to synthesize their own cholesterol. Individuals with a high rate of cholesterol synthesis had a higher rate of cholesterol synthesis during both the placebo and plant sterol periods compared to the other participants. However, cholesterol absorption was decreased due to plant sterol consumption, with no difference between the two groups. There was no change in circulating LDL-cholesterol concentration; change in cholesterol absorption following plant sterol consumption did correlate with the change in the rate of cholesterol synthesis. These findings suggest that as cholesterol absorption was lowered, there was a reciprocal increase in cholesterol synthesis; however, this did not associate with a change in circulating LDL-cholesterol concentration. These findings indicate that plant sterol consumption lowers cholesterol absorption; however, other mechanisms likely influence whether this decrease in cholesterol absorption results in a decrease in circulating cholesterol. Research continues with investigating metabolic flexibility, an approach that we are researching as a metabolic marker in the development of insulin resistance and type 2 diabetes. Obesity is a major public health concern in the United States and globally. The increased incidence of obesity results in an increased risk of developing type 2 diabetes. This research is conducted in support of objective 2 (to determine the influence and interaction of the composition of food intake and exercise on glucoregulation, cardiometabolic profile, and metabolic flexibility (fuel management)). Metabolic flexibility is defined as the body’s ability to switch among the metabolic fuels (protein, fat or carbohydrate) that we burn (oxidize) in our body to support our energetic (caloric) demands. Metabolic flexibility is related to the availability of the metabolic fuels, and it is commonly measured as the change in respiratory quotient (measuring oxygen breathed and carbon dioxide exhaled) from the fasted state to the insulin-stimulated state. Typically, this measurement is performed using a euglycemic-hyperinsulinemic clamp and hood calorimetry both of which are cumbersome measurements. A study was performed to evaluate if room calorimetry alone could provide the same results. During 24-hour measurements in the room calorimeter on four separate occasions, research volunteers participated in meal and exercise challenges. These challenges included exercise sessions on a treadmill (high intensity – short duration or low intensity – long duration) and consumption of one of two treatment beverages for lunch (high carbohydrate or high fat shake). Metabolic flexibility was calculated in a manner similar to the literature, and new metabolic flexibility variables were also evaluated. Post-lunch rate of change of respiratory quotient was significantly larger following the high carbohydrate shake compared to the high fat shake. The rate of change of the increase in respiratory quotient following the start of exercise was negatively correlated with age and body fat. This study shows that the non-invasive room calorimetry method can be used to measure many metabolic flexibility variables. To improve research results associated with objective 2 (to determine the influence and interaction of the composition of food intake and exercise on glucoregulation, cardiometabolic profile, and metabolic flexibility (fuel management) studies were conducted to improve the accuracy and efficacy of respiratory-exchange-ratio measurement in order to provide low-cost, widely accessible tracking of personal fuel utilization. The interest in measuring stand-alone respiratory-exchange-ratio is motivated by a metabolic state model that suggests respiratory-exchange-ratio may be a simpler and more informative metric to track for weight management than traditional calorie intake and expenditure tracking. Additionally, the capability to measure respiratory-exchange-ratio any time, and track trends over long time periods and diverse activities, presents intriguing possibilities for endurance training. Two approaches were used to improve analysis of calorimetry (breath gas) data, including deconvolution (this is a common mathematical/engineering technique used to separate different influences over output data collected at frequent intervals) and resampling methods (statistical techniques which basically extend the data set to provide more reliable measures of the population statistics). This research improves the capability of scientists to determine energy expenditure and burning of fat and carbohydrate with much greater accuracy.
1. Calorie content of walnuts is less than previously thought. Continuing with research conducted with pistachios and almonds, ARS researchers in the Beltsville Human Nutrition Research Center, Beltsville, Maryland, discovered the calorie content of walnuts is 21% less than what is found using the current method for measuring calories for food labeling (a calculation using the Atwater factors). The discrepancy between the measured metabolizable energy value and the value estimated by use of the Atwater factors for walnuts is similar to the discrepancy for almonds. The discrepancy was less, however, for pistachios. The reason for these differences among nuts is unclear. Nevertheless, walnuts are the third tree nut for which the currently used method for determining calories is inaccurate. Each of these tree nuts are excellent or good sources of nutrients, including key essential nutrients that are not consumed in sufficient quantity by most Americans (short-fall nutrients). Some consumers avoid these nutrient-dense nuts over concern that they contain excessive calories. The current research with walnuts and previous research with almonds demonstrates that the calories in these nuts are significantly lower than previously known. This research helps to explain the observations that consumers of nuts do not gain excessive weight. This new research is affecting food labeling and should help consumers to make healthier food choices.
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