The processes of planning and nutrient analyses of diets for controlled feeding trials in free-living subjects
Van der Watt, Izette
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Motivation: There is an increased tendency in the field of nutrition research to conduct human feeding studies in order to test diet-disease hypotheses. Using well controlled feeding approaches subjects consume only foods that have been precisely formulated and prepared in a research kitchen. The development of these accurate experimental diets is essential in order to meet the study objective and provide valid scientific data. Research dieticians use computerised nutrient databases to design these diets that meet the study protocol diet specifications. In most trials the developed experimental diet is chemically analysed to validate the menu. Chemical analysis is an expensive and time consuming procedure and if analysis presents with different nutrient content than planned, adjustments to the menu will follow and a possible repeat of the chemical analysis for verification, adding to the costs of the trial. Limited information has been published regarding the procedures for the planning and nutrient analysis of diets for controlled feeding trials thus, research teams are depending on trial and error experiences in order to guide them in the processes of planning and nutrient analysis for controlled feeding trials in free-living subjects. Objectives: The main aim of this study was to describe the processes of planning and nutrient analyses of diets for controlled feeding trials in free-living subjects. •The first objective was to develop appropriate methodologies for the planning of diets for controlled feeding trials in free-living subjects. Subsequently these recommended steps were used in developing a seven day menu cycle for a controlled feeding trial. •Secondly, the reliability of the two nutrient databases available in South Africa was tested by comparing the nutrient analysis of the menu as calculated by the databases with each other, as well as comparing it to the standard reference of chemical analysis. Methods: •The appropriate menu design methodology to be used in controlled feeding trials: In this study a literature search was conducted using electronic scientific journal databases. This literature search was done in order to locate published controlled feeding trials which described the methodology used for menu design. The information was summarised and a flow diagram was compiled presenting the identified steps that will guide the research team. •The process of nutrient analysis for controlled feeding trials: A comparative study of two South African nutrient databases with chemical analysis: A seven day menu providing 7500kJ/day (35% of the total energy as fat. 17% as protein and 48% as carbohydrates) was developed. The menu was then entered into FoodFinder3 and Dietary Manager Software programmes and nutrient analysis was done. Food prepared in the research kitchen, North-West University. Potchefstroom, South Africa, according to this menu was then chemically analysed for the macronutrient profiles (carbohydrate, fat, protein and fibre, soluble and insoluble fibre) and fatty acid distribution (saturated fatty acids, monounsaturated fatty acids and poly-unsaturated fatty acids) using standard methods. Differences between the different nutrient analyses were compared with non-parametric statistical tests by using the computer software program Statistica. Results: •The appropriate menu design methodology to be used in controlled feeding trials: Ten steps were identified and described in detail that will guide the research team in menu development for controlled feeding trials in free-living subjects. •The process of nutrient analysis for controlled feeding trials: A comparative study of two South African nutrient databases with chemical analysis: The nutrient content of the two nutrient databases did not differ significantly from each other, however, there were differences between the chemical analysed values and the databases calculated values. There were no significant differences between the amount of total energy, protein, carbohydrate, poly-unsaturated fatty acids and total fibre. The total fat, saturated fatty acids and mono-unsaturated fatty acids content using both FoodFinder363 and Dietary Manager were statistically and practically significantly higher than the chemical analysed values (p40.05). FoodFinder3B produced significantly lower levels of insoluble and soluble fibre compared to the chemical analysis. The main factors that were identified that could have contributed to these variations include the use of recipes and combination dishes not available on the database; variations in the fat content of meat dishes, and incomplete data of key nutrients in nutrient databases Conclusion: The 10 recommended steps need to be followed by the research team in order to accurately formulate, plan, produce and deliver research diets. There are important considerations to remember that might influence the success of the menu and the feeding trial. The use of computerised nutrient databases in menu design for controlled feeding trials is functional and assists the research dietician with this challenging task. However, computer nutrient databases are not reliable enough to exclude the step of menu validation by chemical analysis.
- Health Sciences