Design and quality control issues related to dietary assessment, randomized clinical trials and meta-analysis of field-based studies in developing countries.

The essential design and quality control aspects of dietary assessment, randomized controlled trials (RCT) in developing countries and their subsequent meta-analysis are reviewed. Dietary assessment protocols consist of three stages: measurement of food intakes using a method appropriate for the study objectives, calculation of nutrient intakes and finally an evaluation of their nutrient adequacy. The latter may involve: 1) assessment of dietary diversity (average number of different foods consumed per day) and selected indices of dietary quality such as intakes of animal source foods (g/d); 2) percentage of energy from protein, fat and animal protein; 3) selected nutrient densities; and 4) dietary phytate:zinc molar ratio, as well as the prevalence of inadequate nutrient intakes calculated using a probability approach. To establish causality between the nutrient inadequacies identified and adverse health outcomes, RCT must be undertaken. A prerequisite of RCT is double-blind randomization, a procedure designed to eliminate biases arising from baseline confounding variables, unintended interventions and ascertainment bias. Results from existing RCT can be summarized via meta-analysis to gain a better understanding of the population relationship. Meta-analysis is a statistical technique involving linear models or generalized linear models, which can be performed after locating the individual studies, and selecting and abstracting all the necessary data.