A Transformation Approach to Estimating Usual Intake Distributions

Current concerns over links between diet and health, the safety of food, and developing effective nutrition education and food assistance programs have placed increasing demands on federal data collection and methods of monitoring the food supply. Design of effective food and nutrition policies, efficient allocation of resources, and more precise targeting of programs require good estimates of the percentage of the population with deficient, or excess, nutrient or other food component intake. An individual\u27s mean daily intake of the dietary component is a good estimate of the individual\u27s dietary status. However, to evaluate dietary adequacy of a population it is necessary to obtain an estimate of the distribution of usual intakes. Often, the distribution of usual intakes is estimated from the distribution of mean daily intakes. Further, it is usually assumed that usual intakes of nutrients are normally distributed. Two problems arise. First, distributions of usual intakes for most nutrients are skewed. Second, the variance of the distribution of mean daily intakes is larger than the variance of the true usual intake distribution, due to within-individual variability of daily intakes. Some proposed adjustments produce the correct mean and variance in the estimated distribution, but fail to correct the skewness, unless the true distribution of usual intakes is normal. We describe a method for estimating usual intake distributions which does not assume normality, and which takes into account the within-individual variation in daily intake. The method consists in transforming the dietary data from the original space into normal space, and predicting the usual daily intakes in normal space. Inferences about the dietary status of the population can then be made in normal space. Alternatively, predicted normal usual intakes can be transformed back to obtain a set of pseudo usual intakes in the original scale

Critique of Two Methods for Assessing the Nutrient Adequacy of Diets

The adequacy of diets can be assessed using several analytical approaches. This paper reviews two methods of assessment: a cutoff method, which estimates the percentage of the population having usual intakes below a given value; and a probability method, which assesses the percentage of the population whose usual intakes are below their individual requirements. First, the concept of usual nutrient intakes and the problems associated with estimating usual intake distributions are discussed. Next, the two methods of dietary assessment and their related assumptions are described and compared. The more specific inference of the probability method is shown to rely on its assumptions and data that are currently not available. While the cutoff method is simpler, its use may result in misclassification errors and its estimates are highly influenced by the cut-off standard selected.

A TRANSFORMATION APPROACH TO ESTIMATING USUAL INTAKE DISTRIBUTIONS

Design of effective food and nutrition policies, efficient allocation of resources, and more precise targeting of food programs require good estimates of the percentage of the population with deficient, or excess, nutrient or other food component intake. An individual\u27s mean daily intake of the dietary component is a good estimate of the individual\u27s dietary status. However, to evaluate dietary adequacy of a population it is necessary to obtain an estimate of the distribution of usual intakes. Often, the distribution of usual intakes is estimated from the distribution of mean daily intakes. Two problems arise. First, distributions of usual intakes for most nutrients are skewed. Second, the variance of the distribution of mean daily intakes is larger than the variance of the true usual intake. distribution, due to within- individual variability of daily intakes. We describe a method for estimating usual intake distributions which does not assume normality, and which takes into account the within-individual variation in daily intake. The method relies on appropriate transformation of the dietary data from the original space into normal space

Usual energy and macronutrient intakes in 2-9-year-old European children

OBJECTIVE: Valid estimates of population intakes are essential for monitoring trends as well as for nutritional interventions, but such data are rare in young children. In particular, the problem of misreporting in dietary data is usually not accounted for. Therefore, this study aims to provide accurate estimates of intake distributions in European children. DESIGN: Cross-sectional setting-based multi-centre study. SUBJECTS: A total of 9560 children aged 2-9 years from eight European countries with at least one 24-h dietary recall (24-HDR). METHODS: The 24-HDRs were classified in three reporting groups based on age- and sex-specific Goldberg cutoffs (underreports, plausible reports, overreports). Only plausible reports were considered in the final analysis (N=8611 children). The National Cancer Institute (NCI)-Method was applied to estimate population distributions of usual intakes correcting for the variance inflation in short-term dietary data. RESULTS: The prevalence of underreporting (9.5%) was higher compared with overreporting (3.4%). Exclusion of misreports resulted in a shift of the energy and absolute macronutrient intake distributions to the right, and further led to the exclusion of extreme values, that is, mean values and lower percentiles increased, whereas upper percentiles decreased. The distributions of relative macronutrient intakes (% energy intake from fat/carbohydrates/proteins) remained almost unchanged when excluding misreports. Application of the NCI-Method resulted in markedly narrower intake distributions compared with estimates based on single 24-HDRs. Mean percentages of usual energy intake from fat, carbohydrates and proteins were 32.2, 52.1 and 15.7%, respectively, suggesting the majority of European children are complying with common macronutrient intake recommendations. In contrast, total water intake (mean: 1216.7 ml per day) lay below the recommended value for >90% of the children. CONCLUSION: This study provides recent estimates of intake distributions of European children correcting for misreporting as well as for the daily variation in dietary data. These data may help to assess the adequacy of young children's diets in Europe