Introduction to the toxicological aspects of nutrient intake

101 Toxic Food Ingredients

101 Toxic Food Ingredients

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This chapter focuses on the toxicological aspects of a special group of substances, the nutrients. With respect to nutrient intake two points are of high toxicological importance.

First, attention should be paid to the margin between physiological need and toxic intake, i.e., dose. On the one hand, nutrients are necessary for life and good health, on the other, they may pose life threatening risks. When the intake of nutrients is very low, this may lead to lethal deficiencies, whereas a very high intake may cause toxic effects. The requirements for optimal nutrient intake are based on both deficiency and toxicity data. The optimal intake of a nutrient may be defined as the intake that meets the minimal physiological needs of an organism for that nutrient, and does not cause adverse effects. An example of the implications of overintake is the acute vitamin A toxicity in Arctic and Antarctic explorers on the consumption of polar bear liver containing about 600 mg retinol per 100 g liver. The explorers were informed by the Eskimos that eating polar bear liver may cause drowsiness, headache, vomiting, and extensive peeling of the skin.

A second point that deserves attention with respect to nutrients is the possible interaction between components of a diet. If there is an interaction, there is no adequate procedure to evaluate the toxicological safety, since the traditional procedure for the evaluation of toxicological safety is inappropriate. For example, if a meal consists of protein-rich fish or fish products, and green leafy vegetables, like spinach, interaction may occur leading to the formation of nitrosamines (e.g., dimethylnitrosamine) in the stomach. Dimethylnitrosamine has been shown to induce tumors in experimental animals.

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concentration food - oriented chemicals: food additives, and contaminants concentration food - oriented chemicals: food additives, and contaminants

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Figure 12.1 Impact of concentration on health in the case of food-oriented substances, such as food additives and contaminants. A, no-observed-adverse-effect concentration (acceptable daily intake, ADI); B, no-observed-adverse-effect level (NOAEL); C, minimum-observed-adverse-effect level; D, lethally high concentration; C1-D1, genotoxic substances such as nitrosamines; A2-D2 food contaminants such as nitrite; A3-D3, food additives such as benzoic acid; A4-D4, toxins of microbial origin such as botulinum toxin; f, safety margin.

The actual toxicological risks associated with the intake of excessive amounts of nutrients differ from nutrient to nutrient. For instance, induction of toxic effects is hard to imagine after vitamin C intake, while vitamin A poisoning following the consumption of livers of animals high in the food chain, as in the example described above, is well-known. If common nutrients pose health hazards, they must be either highly active or accumulate to a high degree in tissues. In order to gain more insight into the toxicological aspects of nutrient intake, it is useful to divide food chemicals into two groups: food-oriented and body-oriented chemicals.

Food-oriented chemicals have no nutritional value and are primarily associated with food. The group of food-oriented chemicals includes food additives (preservatives such as benzoic acid), antioxidants (butylated hydroxyanisole, BHA), (sweeteners, such as sorbitol), food contaminants (nitrate and nitrite, lead and cadmium, polycyclic aromatic hydrocarbons), and natural toxins (aflatoxins). Assessment of the toxicological risks from the intake of food-oriented chemicals is based on the results of extensive, carefully regulated toxicological screening. Therefore, food-oriented chemicals are considered to be relatively safe (see Figure 12.1). The toxicology of these substances is discussed in Chapters 9, 10, and 11 in more detail.

Body-oriented food chemicals are the nutrients. Nutrients are necessary for growth, maintenance, and reproduction of living organisms (body-oriented). They are divided into two groups: macronutrients (fats, carbohydrates, and proteins) and micronutrients (vitamins and minerals, including trace elements).

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concentration toxicity optimal activity low activity deficiency body - oriented chemicals: nutrients, hormones and drugs

Figure 12.2 Impact of concentration on health in the case of body-oriented substances, such as nutrients, hormones and drugs. A, lethally low concentration; B, minimum concentration compatible with good health; C, concentration for optimal health (nutrients; Recommended Dietary Allowance, RDA); D, maximum concentration compatible with good health; E, lethally high concentration. A1-E1, hydrophilic vitamins such as vitamin C and B1; A2-E2, lipophilic vitamins such as vitamin A and E, or selenium; A3-E3, macronutrients such as fat; f, safety margin.

For the intake of nutrients recommended dietary allowances (RDAs) are set by official committees. RDAs are defined as the intake levels of essential nutrients that (on the basis of present scientific knowledge) meet the needs of practically all healthy persons. Generally, these levels are considered to be safe (see Figure 12.2 and Table 12.1).

In the next sections, the present knowledge of the toxicity and safety of a number of selected nutrients are discussed. A more extensive study of nutritional toxicology is beyond the scope of this textbook. (For information about nutrients that are not discussed here see the reference list).

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