Diet design for a multicenter controlled feeding trial: The DELTA program

Objective To describe the process and results of diet standardization, diet validation, and monitoring of diet composition, which were key components of protocol 1 of Dietary Effects on Lipoproteins and Thrombogenic Activity (DELTA-1), the initial protocol in a program of multicenter human feeding studies designed to evaluate the effects of mount and type of fat on lipoproteins and hemostasis parameters in various demographic groups. Design DELTA-1 was based on a randomized, blinded, crossover experimental design. Three diets were fed for 8 weeks to 103 healthy men and women aged 22 to 67 years at 4 field centers. Diet A, an average American diet, was designed to provide 37% of energy from fat, 16% of energy from saturated fatty acids (SFAs); diet B (step 1 diet) was designed to provide 30% of energy from fat, 9% of energy from SFA; and diet C (low SFA diet) was designed to provide 26% of energy from fat, 5% of energy from SFA. Key features of diet standardization included central procurement of fat-containing foods, inclusion of standard ingredients, precision weighing of foods-especially sources of fat and cholesterol-and use of standardized written procedures. Setting For menu validation, a set of 12 menus for each diet was prepared in duplicate and chemically assayed. For monitoring of diet composition during the study, an 8-day diet cycle (6 weekday and 2 weekend menus) was sampled by every field center twice during each of 3 feeding periods. Statistical analyses Means (+/-standard error) were calculated and compared with target nutrient specifications. Results DELTA-1 was able to provide a standardized diet that met nutrient specifications across 4 field centers over 24 weeks of participant feeding spanning a total of 8 months. Applications Prestudy chemical validation of menus and continuous sampling and assay of diets throughout the study are essential to standardize experimental diets and to ensure that nutrient target goals are met and maintained throughout a controlled multicenter feeding study.