Nutrition assessment and dietary guidelines: experience from the Dutch Nutrition Surveillance System

Assessment of intake from the diet

Exposure assessment is one of the key parts of the risk assessment process. Only intake of toxicologically significant amounts can lead to adverse health effects even for a relatively toxic substance. In the case of chemicals in foods this is based on three major aspects: (i) how to determine quantitatively the presence of a chemical in individual foods and diets, including its fate during the processes within the food production chain; (ii) how to determine the consumption patterns of the individual foods containing the relevant chemicals; (iii) how to integrate both the likelihood of consumers eating large amounts of the given foods and of the relevant chemical being present in these foods at high levels. The techniques used for the evaluation of these three aspects have been critically reviewed in this paper to determine those areas where the current approaches provide a solid basis for assessments and those areas where improvements are needed or desirable. For those latter areas, options for improvements are being suggested, including, for example, the development of a pan-European food composition database, activities to understand better effects of processing on individual food chemicals, harmonisation of food consumption survey methods with the option of a regular pan-European survey, evaluation of probabilistic models and the development of models to assess exposure to food allergens. In all three areas, the limitations of the approaches currently used lead to uncertainties which can either cause an over- or underestimation of real intakes and thus risks. Given these imprecisions, risk assessors tend to build in additional uncertainty factors to avoid health-relevant underestimates. This is partly done by using screening methods designed to look for "worst case" situations. Such worse case assumptions lead to intake estimates that are higher than reality. These screening methods are used to screen all those chemicals with a safe intake distribution. For chemicals with a potential risk, more information is needed to allow more refined screening or even the most accurate estimation. More information and more refined methods however, require more resources. The ultimate aims are: (1) to obtain appropriate estimations for the presence and quantity of a given chemical in a food and in the diet in general; (2) to assess the consumption patterns for the foods containing these substances, including especially those parts of the population with high consumption and thus potentially high intakes; and (3) to develop and apply tools to predict reliably the likelihood of high end consumption with the presence of high levels of the relevant substances. It has thus been demonstrated that a tiered approach at all three steps can be helpful to optimise the use of the available resources: if relatively crude tools - designed to provide a "worst case" estimate - do not suggest a toxicologically significant exposure (or a relevant deficit of a particular nutrient) it may not be necessary to use more sophisticated tools. These will be needed if initially high intakes are indicated for at least parts of the population. Existing pragmatic approaches are a first crude step to model food chemical intake. It is recommended to extend, refine and validate this approach in the near future. This has to result in a cost-effective exposure assessment system to be used for existing and potential categories of chemicals. This system of knowledge (with information on sensitivities, accuracy, etc.) will guide future data collection.

Dependence of dietary intake estimates on the time frame of assessment

Food chemical risk management needs, among other things, assessment of exposure. For dietary intake food consumption surveys are the data source to be used. One complicating factor in the usage of these data is the dependence of dietary intake estimates on the time frame of assessment. Central to this time dependence is the within-subject variation regarding the usage of food products and, as a consequence, the intake of chemicals. Within-subject variation is mostly as large as or larger than between-subject variation. Expressed per kilogram body weight, average (total) variation in intake variables depends on the age group, with variation usually being greater at younger age, most likely as a result of the higher intake levels at that age. Combination of age groups results in an increase in between-subject variation, and correction based on the figures for the total population will be too small. Ideally, exposure data for all days of one's life should be available to assess lifetime exposure. Since information on all these days is not an attainable and practical option, and not an option to strive for either, the most recent available data should be used that can be extended with simulation studies to anticipate future developments. The present food consumption surveys available in European countries are based on data that vary from 1 day (24-h recall and dietary record) to habitual intake (dietary history and food frequency). The data of a survey based on 1 day refer to 0.004% of an average lifetime of 70 years. Based on the demographic picture of the population, a reasonable approximation of lifetime intake can be obtained. The proportion of users and the consumption level among users depend on the time frame of assessment, especially for irregularly consumed products. Usage of the concept of "users only" overestimates lifetime exposure of the population, the extent of overestimation depending on the duration of the survey. The likelihood that all consumers have been exposed to a chemical once during a lifetime period is realistic in the sense of the best approximation of reality. As a result of this assumption all exposure assessments will have a similar point of departure and the dependence of the results on the food consumption method will be reduced.

Food-based dietary guidelines: some assumptions tested for The Netherlands

Recently, the concept of food-based dietary guidelines has been introduced by WHO and FAO. For this concept, several assumptions were necessary. The validity and potential consequences of some of these assumptions are discussed in this paper on the basis of the Dutch National Food Consumption Surveys. The topics were interrelationships among dietary characteristics, nutrient density, diets in accordance with the guidelines, and food variety. To obtain insight into overall diet quality, a dietary quality index based on nutrients and a food-based quality index based on food groups were created and tested. As expected the results showed that a higher dietary quality index was associated with an improved intake of the nutrients included in the index, in particular a lower intake of total fat and cholesterol. This was related to a lower consumption of cheese, fats and oils, meat and meat products, and a higher consumption of fruit and vegetables. The information obtained with a dietary quality index can be used to assess the feasibility of a particular goal in combination with other relevant goals and to obtain clues or confirmation for recommendations regarding food consumption. The food-based quality index created showed that a combination of several food-based goals (formulated in quantitative terms) was associated with an increase in food consumption, without a clear relevance for the dietary quality. Therefore, the formulation of food-based guidelines should be based on explicitly stated dietary goals. The findings regarding nutrient density were in the direction of what was assumed, namely a positive association between density and absolute intake, although the expected effects were not completely found. The results regarding the association between variety and dietary intake were characterized mainly by differences in quantity rather than dietary quality. The data indicate that energy intake may be an important pitfall in implementing food-based dietary guidelines, that 'eat a variety of food' can be an empty slogan and that nutrient density is positively related to the absolute intake of specific micronutrients. Further, the 'absence' of interrelationships among risk nutrients indicates that a selection process has to be applied.

Patterns of food and nutrient intakes of Dutch adults according to intakes of total fat, saturated fatty acids, dietary fibre, and of fruit and vegetables

Dietary intake characteristics were studied among 3833 adults of the second Dutch National Food Consumption Survey held in 1992. The subjects were classified into three groups based on their intake of total fat (% energy), saturated fatty acids (% energy), dietary fibre (g/MJ), and fruit and vegetables (g/d). All the classifications resulted in differences in energy intake. Except for dietary fibre, the mean energy intake was higher in the higher-intake tertiles. For the classification based on total fat, saturated fatty acids and dietary fibre the more prudent diets were accompanied with a lower energy-intake. As to the consumption of food groups, differences existed in both the proportion of consumers and in the mean consumption among users. It is concluded that the trends observed are probably more important than the actual figures.