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 c omponents of protocol 1 of Dietary Effects on Lipoproteins and Thrombo genic Activity (DELTA-1), the initial protocol in a program of multice nter human feeding studies designed to evaluate the effects of mount a nd type of fat on lipoproteins and hemostasis parameters in various de mographic groups. Design DELTA-1 was based on a randomized, blinded, c rossover 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 f at, 16% of energy from saturated fatty acids (SFAs); diet B (step 1 di et) 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 f rom fat, 5% of energy from SFA. Key features of diet standardization i ncluded central procurement of fat-containing foods, inclusion of stan dard ingredients, precision weighing of foods-especially sources of fa t and cholesterol-and use of standardized written procedures. Setting For menu validation, a set of 12 menus for each diet was prepared in d uplicate and chemically assayed. For monitoring of diet composition du ring the study, an 8-day diet cycle (6 weekday and 2 weekend menus) wa s sampled by every field center twice during each of 3 feeding periods . Statistical analyses Means (+/-standard error) were calculated and c ompared 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 c ontinuous sampling and assay of diets throughout the study are essenti al to standardize experimental diets and to ensure that nutrient targe t goals are met and maintained throughout a controlled multicenter fee ding study.