What is really dangerous in our diet?
All living creatures need to control the risks of food – in fact it is an essential strategy for survival. This is true even for single-cell organisms. This is because many substances in soil and water are detrimental to life. Arsenic and mercury, for instance, disturb the functions of many proteins. Organic substances are important sources of energy and the building blocks of the organism, but many of them are poisonous themselves or can form poisonous metabolites. Moreover many organisms attempt to prevent others from eating them or otherwise competing for their living space, and their defence mechanisms often include poisons. These organisms come from all classes, from the most primitive microbes to plants and animals. Mushrooms are well known for their poisons, plants contain alkaloids, and frog skin can be highly neurotoxic.
Even some of the very common cultivated plants are only today safe because they have been subjected to selective breeding, e.g. the wild forms of potato contain solanine. This might cause stomach pain, diarrhoea and even convulsions. Solanine is present in most parts of the potato plant, but selective breeding has decreased its levels to very low amounts in the edible part. However, if potatoes are kept in sunlight, or if they start budding, the solanine concentrations increase. Another typical rather poisonous cultivated plant is cassava (manioc). A cyanide-producing glycoside occurs in varying amounts in different varieties of cassava, and they have to be removed by complex refining systems. So it is worth remembering that eating “natural” foods and experimenting in the kitchen with new vegetables and plants are not risk-free activities.
Previously in Europe the most important chemical hazard in food was the ergot alkaloids produced in rye by the fungus Claviceps purpurea forming sclerotia. These alkaloids include ergotamine which was earlier used as a drug for treating migraine headache. Ergotamine poisoning causes extreme constriction of blood vessels, vascular damage and even gangrene of extremities. There was a disastrous ergot epidemic in France in the eighteenth century with 8,000 deaths, but as late as 1953 there was another epidemic. In most countries, seed control and technical developments as well as fungicides have helped to avoid these major calamities.
Safety based on selectivity
Since food can be poisonous, both herbivorous and carnivorous animals have to be selective in what they eat. Seeds and fruits are often nourishing and safe, because animals utilising them take part in the dispersal strategy of the plants. When a bird eats a cherry, the stony seed is preserved and deposited at a distance from the parent tree with fertilization following the deposition.
The safety and nutritional value of many cultivated plants are, however, based on selective plant breeding, and various common plant species may be quite far removed to the original natural ancestor. In animals there is also an efficient enzymatic machinery for turning foreign compounds into non-toxic metabolites to use them as an energy source, or at least rendering them water soluble so that they can be excreted out of the organism. These same enzyme systems handle synthetic compounds in the same way, although there are some notorious exceptions.
The most problematic health hazard concerning food is cancer. It has long been recognized that food is one of the most important risk factors for cancer. On the other hand, it has been known for a long time that this is not due to individual chemicals in food, but the food itself, its major components, and especially the total energy content, fat content and the balance between fat, meat and vegetables and fruit. Therefore the cancer risk, similarly to the risk of cardiovascular diseases, is dependent on the amount of food and its major constituents.
Food allergies usually mean sensitization to specific food items such as fish proteins, nuts or chocolate, but occasionally to food additives such as benzoic acid. A different kind of hypersensitivity is also known that is not based on immunological mechanisms, an example is sensitivity to azo dyes.
Understanding, less rigidity
The food properties described above lead to some obvious conclusions. There is no point talking only of chemicals added by man or present as contaminants from the environment. One has to deal simultaneously with all chemicals, man-made and natural. In some conditions, the synthetic chemicals do not increase risks, but rather decrease them. One example is the preservatives that prevent microbial growth and food poisonings.
Even some chemical hazards can be combatted by chemicals. Fungicides stop the growth of the fungus Aspergillus flavus, and so prevent formation of the carcinogenic aflatoxins in food products. Nitrites inhibit the growth of the bacterium Clostridium botulinum, and so prevent the production of the deadly botulinum toxin. Antioxidants are believed to decrease cancer risks. Many plants produce toxins to defend themselves against attack by pest species such as insects or fungi. Therefore pesticides may decrease the synthesis of the plant’s own toxins that often are much more toxic than the pesticide. A decrease of pesticide use on the other hand could lead to increased production of toxins.
Hence the question of chemical risks of food is very complicated indeed, and sometimes measures that seem crystal clear and logical are no such thing at all. Risk management requires a thorough comprehension of all aspects of the situation, and even alternative risks. Oversimplified enthusiasm in attempting to decrease one risk may sometimes increase the entire risk.
Food has caused many kinds of risks during the history of mankind, microbiological food poisonings, contaminant risks, and risks by natural toxins. In highly developed societies, the chemical risks are probably the least likely to occur because of strict controls. In the developing countries, the situation is very different.
Notes and references
- Alkaloids are organic bases (alkaline compounds) that contain in addition to carbon and hydrogen also nitrogen. Examples are caffeine, morphine, quinine, strychnine etc.
- Solanine is a glycoalkaloid (alkaloid containing sugar groups) typical of potato and tomato and related plants.
- Glycosides are sugar-containing active natural compounds that are often poisonous.
- Sclerotia are hardened mass of fungal growth allowing the fungus to lie dormant for long periods.
- Immunology deals with natural defence mechanisms of the body e.g. towards bacteria. The defences are based both on specialized cells and on antibodies, proteins that specifically bind to foreign substances, especially foreign proteins. The purpose is to neutralize the effects of the intruders, and/or to mark them to indicate that they should be destroyed by specific defence cells. Sometimes the defence mechanisms are directed to the wrong targets such as pollens, causing allergic reactions, or towards own tissues, causing autoimmune disease.
One level up: Is man defiled by what goes to his mouth?
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