For years, I’ve enjoyed a certain wry bemusement from the dietary restrictions imposed by the world’s various religions. It seems obvious to me that the vast majority of such rules were based upon common-sense recommendations for healthy eating from a pre-refrigeration age. Some rules do seem to have passed their “best-before” date: a favourite of mine that few of us obey is the rule that it’s OK to eat locusts but not prawns (Leviticus 11:9-22).

One such rule I learnt for the first time a day or so ago, as part of reading about the ancient Greek philosophers. It concerns the followers of Pythagoras – he of right-angled triangles fame – and the absolute no-no of eating beans.

Some background may help here. It turns out that Pythagoras was not just a mathematician and geometer but also a leader of a religious and political cult. Followers believed in reincarnation and that some or all living things – animals and plants – have souls. (There seems to be some measure of disagreement among the Pythagoreans whether all animals had souls and they were even less sure about plants, although they all seemed to agree that laurel bushes did.) Strictly interpreted, about all that was safe to eat was milk and honey: that steak or bunch of olives you’re tucking into just might contain the soul of your dearly-departed granny, so best avoided, eh? These rules were frequently broken, but they were all sure about the beans.

The Pythagoreans faded away about 2400 years ago and subsequent generations of Greeks thought the practice odd and speculated wildly on the origins of the “no beans” rule. Suggestions in circulation included:

• the flatulence beans cause disturbs our sleep and mental tranquillity
• beans are testicle-shaped
• they are shaped like the Gates of Hades
• they are shaped like the universe
• they are used in allotting political office (Pythagoreans were no democrats)
• buried in manure, they take on human shape
• their stems are hollow and so connect directly to the underworld.

More modern research suggests a more prosaic reason: some people get ill after eating fava beans, which were common in southern Italy where Pythagoras and his cult lived.

What struck me about this story is how easily wild rumours and speculation can gain hold and have some currency – a problem which our modern, digitally connected world can make worse for those who inhabit only those parts of cyberspace populated by like-minded people.

More beans, anyone?