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Rights: University of Waikato
Published 18 March 2011 Referencing Hub media

Polyphenols present in plants we eat are toxic in large amounts, but in small amounts, they are beneficial. Plant & Food Research’s Dr David Stevenson explains this apparent contradiction. David describes a new theory called ‘hormesis’ that has evolved from the debate around this contradiction.

Point of interest
Botulinum toxin type A is an injectable neurotoxin, that is, a toxin that blocks the ability of nerves to make muscles contract. It paralyses muscles. It is the most toxic substance known but is used in extremely small amounts in cosmetic surgery to remove frown lines from the brow. If you opt for a Botox treatment, make sure the dose you are receiving is correct.

All things are poisons, and there is nothing that is harmless; the dose alone decides that something is a poison.

Paracelsus (1493–1541)



We used to think that every compound in existence was either good or bad. There were toxins, there were nutrients. Toxins were bad, nutrients were good. What we now know is that there is really nothing that is all good or all bad – it’s all in the dose
There is a new theory of how toxins work called hormesis, which says that a toxin is a compound which is bad for you in excess but may well often be good for you in very small quantities, because it may well stimulate some defensive mechanism in the cells, which not only protects you from that toxin but maybe a lot of other ones. One very good example is actually the polyphenols, because the plants actually don’t make them for our benefit, they make them to be mildly toxic and to make us go away and eat something else.

It has been found from animal studies that, if you feed animals very large amounts of polyphenols – far more than you could possibly get by eating foods – then there are toxic effects. But we also know that small amounts are very beneficial, so basically hormesis says that, if you have the right amount of something, then it’s good for you.

You could probably also apply that to free radicals, whereas large amounts of free radicals will cause all sorts of damage to your cells whereas small amounts are necessary for signalling.

The New Zealand Biotechnology Hub
Dr David Scobie