In a cross-over design, 82 women and men recorded their food intake by a precoded 7-day record book (PR) including both standard portions in household measures and photographs, and a weighed 7-day record (WR), respectively. Single 24-h urine samples, for determination of nitrogen excretion, were collected for 39 subjects during the WR period. Comparing the PR to the WR method, the mean intake of some foods, as cheese, was higher, and bread and vegetables lower. For energy and nutrients, the fat energy percent (E%) was higher, and protein E%, dietary fibre, iron, thiamin, folate, carotene and α-tocopherol were all lower. Protein intake registered by the PR method was 20% lower compared to 24-h urine samples, and 11% lower for the WR method. The results indicate that some of the standard portion sizes, used by the PR method, contributed to the observed differences in food and nutrient intakes. The subjects found it easier and less time-consuming to record their food intake with the PR than with the WR method. The time spent on processing data was reduced by 50% when using the PR method. The results of the study will be used for improvements in the design of the PR for use in large-scale dietary surveys for monitoring dietary habits.
Not only what we eat, but also when we eat seems to be of importance for well-being, nutritional status, and health. The regulation of food intake (amounts) operates through feed backs from the periphery reporting to the central nervous system about the energy content of the body. Timing of eating is controlled by circadian rhythms in activity and sleep, internal rhythms being entrained by the external light-dark rhythm. Disturbed behavioural rhythms, e.g. shift work and travelling across time zones, interact strongly with internal physiology. Life-style in the 24-hour society makes people stay awake, eat and sleep at the wrong times with respect to human circadian rhythms in metabolism and performance.
Nutritional assessment is the interpretation of information obtained from dietary, biochemical, anthropometric and clinical studies. In individuals, qualitative or quantitative food consumption data may be collected by food frequency questionnaires or interviews (retrospective methods), by use of food records (prospective methods); weighed food record, estimated food record or menu record, or by observations. Nutrient values derived from food composition data or direct chemical analysis represent the maximum available to the body and not the amount actually absorbed and utilized. The design of the study is crucial and the methods for carrying it out are aimed at minimizing bias to improve internal and external validity. This paper will focus on factors of importance to improve the internal validity of dietary assessment studies; selection of method; data collection, assessment of nutrient intakes from food consumption data and evaluation of data.