Why one bad meal can put us off a dish for life

·3-min read
Freshly made curry and rice in a cardboard takeaway container sold at Manchester Christmas markets.
One bad curry could flip a 'switch' in our brain that turns us off that dish for life. (Stock, Getty Images)

One dodgy curry could have you swearing off vindaloos for life.

While memories of food poisoning can make a dish unappealing, scientists from the University of Sussex have found a negative meal experience may actually flip a "switch" in our brain.

The team studied snails, who usually slurp up sugar as soon as it is in front of them.

Gently tapping the animals on the head when the sugar appeared altered their behaviour, however, with the molluscs then refusing to eat the sweet stuff even when hungry.

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The scientists discovered so-called "aversive training" essentially caused a switch to flip in the animal's brain, reversing their normal response to the once-loved food.

While snails are a long way from humans, the team believes a similar mechanism may occur in people after a "bad takeaway curry".

snail crawling on a tree close up
The scientists studied snails; 'a similar yet exceptionally basic model of how human brains work'. (Stock, Getty Images)

"Snails provide us with a similar yet exceptionally basic model of how human brains work," said study author Professor George Kemenes.

"In our research, the negative experience the snail had with the sugar could be likened to eating a bad takeaway curry, which then puts us off that particular dish in future.

"We believe in a human brain, a similar switch could be happening where particular groups of neurones [nerve cells] reverse their activity in line with the negative association of a particular food."

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Animals are thought to have evolved "sensory cues" when it comes to food in order to survive.

"Attractive tastes" indicate something is safe to eat, "essential for foraging while the recognition of inedible substrates prevents harm", the Sussex scientists wrote in the journal Current Biology.

Distinguishing these flavours comes naturally, however, the process "can undergo fundamental changes due to prior experience" with the food in question.

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Snails have nerve cells that normally limit their eating habits.

"By suppressing the feeding circuit, it ensures the snail doesn't just eat everything and anything; but when sugar or other food stimulus is present, this neurone becomes inhibited so feeding can commence," said study author Dr Ildikó Kemenes.

Sugar is high in calories, which animals normally seek for energy.

"After the aversive training, we found this neurone reverses its electrical response to sugar and becomes excited instead of inhibited by it," said Dr Kemenes.

"Effectively, a switch has been flipped in the brain which means the snail no longer eats the sugar when presented with it, because sugar now suppresses rather than activates feeding."

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After the sugar-related head tapping, the snails ate a piece of cucumber, suggesting the brain switch trained the animals to reject a specific food.

When the scientists turned off the excited neurone in the snails, the molluscs ate sugar again.

"This suggests the neurone is necessary for the expression of the learned behaviour and for altering the response to sugar," said Dr Kemenes.

"However, we cannot rule out the sugar-activated sensory pathway also undergoes some changes, so we don't make the assumption that this is all that's happening in the brain."

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