Generally, food components are classified into four groups: nutrients, non-nutritive naturally occurring components, including antinutritives and natural toxins, and man-made contaminants and additives. For many food chemicals which are necessary for life, the margin between RDA and minimum toxic dose is often much smaller than a factor 100 or even 2, for example for fat. This is quite understandable, since nutrients play an essential role in the maintenance of homeostases. A slight overintake of nutrients may lead to exceeding the limits within which the homeostases should be kept.
As will be discussed in Section 8.8, there are large gaps in our knowledge of the toxic potential of the majority of natural food components and the consequences of their intake for human health. It is clear that this group of food components should have a high priority with regard to further toxicological research.
The requirements for testing the toxicity of man-made contaminants and their toxico-logical evaluation are similar to those for additives. ADIs are assessed and standards are set.
Before a chemical is admitted as a food additive, extensive toxicological research is required. The results are often the basis for assessing the recommended limit values, such as ADIs, usually applying a safety factor of 100. The levels of additives in food are usually much lower than the ADIs. Therefore, food additives are relatively safe.
Chapters 9 through 12 deal with the toxicology of the various groups of food components in general and the mechanisms underlying their toxic effects in particular. Consumers are increasingly confronted with food products and food components produced with modern technological methods.
Chapter 13 concerns the toxicology of mixtures of the chemical substances that make up our food. It looks at the different types of possible interactions between substances (antagonistic or synergistic) and of independent combined actions of substances (presence or absence of additivity or no additivity).
Not enough is known yet about the prevalence of food allergies and intolerances. Estimates vary widely and are unreliable. It is not easy to diagnose a food allergy and to identify the food component provoking the allergic reaction. The same holds for food intolerance. In Chapter 14, the different types of food allergy and food intolerance and the associated problems are discussed.
The final chapter of Part 2 is an introduction to the use of epidemiological methods in general, and to the application of epidemiology in studying associations between diet and adverse effects of food (components) in particular. The basic principles of epidemiology will be covered at an introductory level. Topics include types of study design, dietary exposure, disease outcome, causality, validity, bias, interpretation and integration of epi-demiological data with animal data. Special attention will be paid to the possibilities and limitations of diet assessment methods and the use of biomarkers in studying diet-disease associations.
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