If you think you might be allergic to nuts then you'll probably want to steer clear of dry roasted peanuts, following new research suggesting that they're more likely to trigger allergic reactions than those that are "raw".
According to the study, the high temperatures involved in dry roasting cause chemical changes that can sensitise the immune system to peanut proteins.
Scientists believe this may explain why peanut allergy is so much more common in the West than in eastern Asia, as dry roasted peanuts are a popular snack in the UK and other Western countries, whereas in the East they are more often used in cooking and eaten raw, boiled or fried.
The research involved comparing the effects of proteins from dry roasted and raw peanuts in mice.
Animals initially exposed to dry roasted peanut proteins subsequently developed a far stronger immune reaction to peanuts.
Dr Amin Moghaddam, from Oxford University, said: "'Our results in mice suggest that dry roasted peanuts may be more likely to lead to peanut allergy than raw peanut.
"The dry roasting causes a chemical modification of peanut proteins that appears to activate the immune system against future exposure to peanuts.
"Allergies in people are driven by multiple factors including family genetic background and exposure to environmental triggers. In the case of peanut allergy, we think we may have discovered an environmental trigger in the way that peanuts are processed by high-temperature roasting."
Professor Quentin Sattentau, who led the team from Oxford University's Dunn School of Pathology, said: "This is the first time, to our knowledge, that a potential trigger for peanut allergy has been directly shown."
But he stressed that the research was at an early stage and it would be premature to avoid roasted peanuts or their products.
He added: "We think we have identified the chemical modifications involved in triggering an allergic response to peanuts, and are currently exploring methods that are food industry-friendly to eliminate these groups."
The findings appear in the Journal of Allergy and Clinical Immunology.
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Previous studies had shown that dry roasting modifies peanut proteins which in turn alters the way the proteins are recognised by the immune system. But until now there was no evidence that eating dry roasted peanuts could trigger an allergic immune response.
The dry roasting process involves temperatures of 160C to 170C or above. At temperatures higher than 130C, a chemical effect known as the Maillard reaction causes changes to specific elements of peanut proteins.
It is this molecular modification that appears to prime the immune system to over-react to peanuts in susceptible individuals.
Peanuts and tree nuts, such as walnuts and cashews, are the most common causes of food allergies in the UK.