Dry roasted peanuts are more likely to trigger an allergy to peanuts than raw peanuts, suggests an Oxford University study involving mice.
The researchers say that specific chemical changes caused by the high temperatures of the dry roasting process are recognised by the body's immune system, 'priming' the body to set off an allergic immune response the next time it sees any peanuts.
The results might explain the difference in the number of people with peanut allergies in the Western world compared to populations in East Asia, the researchers say. In the West, where roasted and dry-roasted peanuts are common, there are far more people with peanut allergies than in the East, where peanuts are more often eaten raw, boiled or fried. Numbers of people with other food allergies show no such difference.
The study is published in the Journal of Allergy and Clinical Immunology and was funded by the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre, the US National Institutes of Health and the Swiss National Science Foundation.
The researchers purified proteins from dry roasted peanuts and from raw peanuts. They introduced the peanut proteins to mice in three different ways - injected under the skin, applied to broken skin, and introduced directly into the stomach. The immune responses of the mice to further peanut extracts given later were measured.
The mice that had been initially exposed to dry roasted peanuts generated greatly increased immune responses to peanuts, compared to mice that had been exposed to raw peanut proteins. The types of immune responses seen are characteristic of allergic reactions.
Professor Quentin Sattentau, who led the research at the Dunn School of Pathology at the University of Oxford, says: 'This is the first time, to our knowledge, that a potential trigger for peanut allergy has been directly shown.'
Previous studies have shown that roasting modifies peanut proteins leading to altered recognition by the immune system, but they did not show that roasted peanuts can trigger an allergic immune response.
First author Dr Amin Moghaddam of Oxford University says: 'Our results in mice suggest that dry roasted peanuts may be more likely to lead to peanut allergy than raw peanuts: 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 Sattentau says: 'We know that children in families with other allergies are more likely to develop peanut allergy. However our research is at an early stage and we think that it would be premature to avoid roasted peanuts and their products until further work has been carried out to confirm this result.'
He adds: '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.'
- Dry roasting involves temperatures of 160-170°C and above. Above 130°C, the Maillard chemical reaction efficiently leads to modification of specific chemical groups in proteins. The products of the Maillard reaction in dry-roasted peanuts can activate a strong allergic immune response, the researchers suggest.
- Allergy UK says allergy to peanut and tree nuts is the most common food allergy in adults and children, with peanut allergy estimated to affect 1 in 50 young infants. The majority of allergic reactions to peanut and tree nuts are mild. However, some allergic reactions to peanut or tree nuts can be severe, causing difficulty in breathing due to asthma-like symptoms or throat swelling, or a drop in blood pressure. This is known as anaphylaxis, and allergy to peanut or tree nuts is one of the most common triggers.
- There is currently no evidence-based advice for prevention of food allergies. It used to be believed that avoiding eating peanuts during pregnancy and when breastfeeding could help reduce the risk but this theory has now been questioned.
- Children are more likely to develop a peanut allergy if they already have a known allergy (such as eczema or a diagnosed food allergy), or there's a history of allergy in their immediate family (such as asthma, eczema or hay fever).
NHS Choices offers advice on food allergies in children here: http://www.nhs.uk/conditions/pregnancy-and-baby/pages/food-allergies-in-children.aspx#close
The paper 'Dry roasting enhances peanut allergic sensitization across mucosal and cutaneous routes in mice' by Amin Moghaddam and colleagues is to be published in the Journal of Allergy and Clinical Immunology with an embargo of 00:01 UK time on Monday 22 September 2014 / 19:01 US Eastern Time on Sunday 21 September 2014.
The study was funded by the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre, the US National Institutes of Health and the Swiss National Science Foundation.
The National Institute for Health Research (NIHR) is funded by the Department of Health to improve the health and wealth of the nation through research. Since its establishment in April 2006, the NIHR has transformed research in the NHS. It has increased the volume of applied health research for the benefit of patients and the public, driven faster translation of basic science discoveries into tangible benefits for patients and the economy, and developed and supported the people who conduct and contribute to applied health research. The NIHR plays a key role in the Government's strategy for economic growth, attracting investment by the life-sciences industries through its world-class infrastructure for health research. Together, the NIHR people, programmes, centres of excellence and systems represent the most integrated health research system in the world. For further information, visit the NIHR website .
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Journal of Allergy and Clinical Immunology