Food toxins

From Ganfyd

Food toxins are responsible for food poisoning which generally relates to agents produced by living organisms that have contaminated normally safe food. This page gives more information about non living toxins and risks with accepted food. It does not consider the risks associated with excessive protein, lipid or carbohydrate consumption.

The issues involved are complex and not always treated objectively due to conflicts of interest that vary between food producers need for income and individual's distorted perceptions of nutrition and risk. Information to consumers by a manufacturer or retailer may be inaccurate or based on inadequate knowledge but often the consumer and their health advisors have similar problems.

Natural Toxins

Intrinsic to the Food

Many foods have intrinsic toxins to man which may be dealt with by

• careful food selection eg
  • Green potatoes - solanine a glycoalkaloid - not eating potato spouts, green (you can remove green areas) or bitter potatoes
  • Apple and pear seeds and the inner stony pit (kernel) of apricots and peaches, almonds - amygdalin converted to cyanide - don't eat more than safe amount of food in question, eg one or two apricot kernels a day.
  • Courgette -cucurbitacins- do not eat if bitter (levels unpredictable but problem rare)
  • Cassava -raw tapioca - cyanide from cyanogenic glycosides - needs proper preparation peeling and cooking
  • Bamboo shoots - cyanide from cyanogenic glycosides - remove outer leaves and any fibrous tissue at the base.
• responsible food preparation eg
  • Rhubarb - oxalic acid - only eat stems - cooking necessary for other toxins.
  • Kidney beans -lectins - Especially red kidney beans - soak the beans for at least five hours and then boil briskly in fresh water for at least 10 minutes - improperly cooked beans can be more toxic than raw ones
  • Lima beans - cyanide from cyanogenic glycosides.
  • Parsnip - Furocoumarins remove diseased areas and always peel
  • Sweet potato (Kumara NZ) - ipomeamarone - remove diseased areas, do not eat if bitter (Note all yams except the Lesser yam (D. esculenta) widely cultivated in Asia, contain the alkaloid dioscorine which is destroyed by cooking, certain yams, contain more toxic alkaloids such as the African bitter yam(D. dumetorum) -dihydrodioscorine or in the case of the Asiatic bitter yam (D. hispida)- larger amounts of dioscorine, which are removed by prolonged boiling and water changing unless as in the later case you use it as an animal hunting poison,
  • Acrylamide from starch-containing foods cooked at high temperatures, such as fried or roasted potato products and bread- safe levels yet to be determined but not an issue with moderate consumption.
  • Lucerne (alfalfa) sprouts contain L-canavanine which induces autoimmune lupus^[1], but this is not an issue at low levels of consumption.
  • Tetrodotoxin by the Japanese but the rest of us are advised to stay well away from puffer fish etc as this is specialised food preparation carried to an extreme some say because of the risk rather than the delicacies taste.
• Some of these toxins such as capsaicin are actually valued components of the food (in moderation) or abused for their properties (eg sugar,salt, alcohol).
• Some may well be found in quantities that are likely to be insignificant such as the carcinogen agaritine in mushrooms with lifetime cumulative cancer risk estimated to be about two cases per 100,000^[2].
• Flavonoids as found as general pigments in plants have such complex properties that generalizations are impossible. For example quercetin which is ubiquitous in the diet might be mutogenic but in mice has distinct anticarcinogenic properties. Similar issues appear to apply to other common food compounds such as allyl isothiocyanate in oil of mustard, horseradish, and cabbage.

Extrinsic to the food

Foods can be subject to contamination during growth, processing and preparation (especially food surfaces)

• Scombrotoxic fish poisoning- bacterial breakdown of fish such as tuna, mackerel producing histamine and other substances that block histamine breakdown. Drugs such as isoniazide and doxycycline can aggrevate by interferring with hepatic histamine breakdown.
• Gastroenteritis
• Enteric pathogens (where there is a link to the HPA guidance on the management of infection with enteric pathogens).

Environmental Toxins

Accidental and Unpredictable Contamination

• Such incidents will always happen
  • Dinoflagellate toxins
    • Paralytic shellfish poisoning from "red tides" such as Alexandrium spp -over 21 known saxitoxins- can be fatal
    • Ciguatoxins causing ciguatera poisoning from toxin accumulation up food chain especially with tropically grown fish - less likely to be serious
    • Neurotoxic shellfish poisoning typically 3 day corse and rarely serious
  • Amnesic shellfish poisoning from diatom Nitzchia pungens concentrated in shellfish

General Environmental Problems

• Dioxins -all foods contain background levels (as they are produced naturally when any organic material is burned) but more will be in animal fats due to food chain accumulation and where industrial exposure takes place
• Polychlorinated biphenols - present since 1930's due to industralisation
• Heavy metals - mining , industrial waste, natural ores

Food Processing Issues

These tend to be recurrent as ignorance is common, and staff may be unaware of issues. Changes in technology, as with composition of soft drinks to allow benzene formation or in the animal rendering process which may have been a factor with BSE can be important.

Food Additives

A wide range of substances are added to food to enhance colour, texture or shelf life. A number have been withdrawn because of toxicity and indeed there is considerable inconsistency worldwide as to which additives are allowed. Studies have been strongly suggestive that one or more of the additives commonly found in sweets are associated with hyperactive behaviour in 3-year-old and 8/9-year-old children^[3][4]:

• Sunset yellow E110
• Carmoisine E122
• Tartrazine E102
• Ponceau 4R E124
• Sodium benzoate E211
• Quinoline yellow E104
• Allura red AC E129

References