Monday September 22 2014
Roasting peanuts may ‘confuse’ the immune system
“Dry-roasted peanuts 'worst for allergies',” the Mail Online reports. New research involving mice suggests that the roasting process increases the "allergic power" of peanuts.
Researchers exposed mice to small amounts of proteins derived from either "raw" peanuts or dry-roasted peanuts, to “prime” their immune systems for an allergic reaction. They later gave them larger doses of the proteins and found that the intensity of the allergic reaction was much larger after priming with the dry-roasted protein, compared with the raw.
The researchers speculated that the roasting process may change the chemical composition of nuts, making them more likely to provoke an allergic reaction.
The research team thought this might partially explain why there is a much higher prevalence of peanut allergies in Western countries – where dry roasting is more common – compared with Eastern countries.
Importantly, the findings were based on mice, so are not directly applicable to humans. Studies involving humans would be needed to better explore these issues. There may be ethical considerations, however, due to the possible risk of anaphylaxis – a severe allergic reaction.
This research alone does not warrant the avoidance of dry-roasted peanuts out of fear of developing a nut allergy. Similarly, if you have a history of nut allergies, you shouldn’t assume that raw, boiled or fried nuts will be safe to eat. Those with an existing allergy should continue to take their normal action to prevent triggering their own allergy, which will vary from person to person.
Where did the story come from?
The study was carried out by researchers from Universities in Oxford (UK) and Philadelphia (US), and was funded by the National Institute for Health Research Oxford Biomedical Research Centre (UK), the National Institutes of Health (US) and the Swiss National Science Foundation Prospective and Advanced Research Fellowships.
The study was published in The Journal of Allergy and Clinical Immunology, a peer-reviewed science journal.
The UK media’s reporting was generally accurate, with some warning against over-extrapolating the results to humans, and that new treatments or allergy-prevention strategies may take a long time to develop, if at all.
What kind of research was this?
This was an animal study, using mice to research allergic reactions to peanuts.
Peanut allergies are relatively common and can be serious, sometimes fatal. The researchers highlight how, despite similar peanut consumption, the Western world has a much higher prevalence of peanut allergy than the Eastern world. The research team suggested that this might be due to the way nuts are prepared. Eastern countries tend to eat their nuts raw, boiled or fried, whereas Western countries consume more dry-roasted nuts.
Researchers often use mice for research purposes because, as mammals, they are biologically similar to humans. Hence, conducting research on mice can tell us what might happen to humans without directly experimenting on them. The caveat is that there is no guarantee the results seen in mice will be applicable to humans; while similar, the biology of the two organisms is not identical, and the differences can sometimes be crucial.
What did the research involve?
The researchers studied the immune response of mice to various peanut products: peanut protein extracted from raw nuts; peanut protein extracted from dry-roasted nuts; raw peanut kernels (grain or seed); and dry-roasted peanut kernels.
The team studied how immune cells reacted to the peanut products and the biochemistry involved in the response.
They studied three main routes of exposure to the peanut products:
- peanut protein extracts were injected into the mice under the skin (subcutaneous route)
- peanut kernels were fed to the mice for them to eat as they normally would (gastrointestinal route)
- extracts were applied to sores in the skin (epicutaneous route)
The main analysis looked at the immune reactions of the mice, comparing raw with dry-roasted peanuts and peanut proteins.
What were the basic results?
The main finding was that the dry-roasted peanut protein extracts and whole peanut kernel elicited a much stronger immune response in the mice than the equivalent raw peanuts and extracts. This occurred consistently across all three exposure routes – on skin, in the stomach and under the skin.
Interestingly, when the mice were “primed” with low levels of dry-roasted peanut proteins to give a low-level reaction, they gave a much larger subsequent reaction to both raw and dry-roasted products. This suggested that exposure to dry-roasted nuts influenced subsequent reaction to raw nuts, possibly sensitising an individual for a strong reaction in the future.
How did the researchers interpret the results?
The researchers indicated that this is the first experiment to show a larger immune response elicited by dry-roasted peanuts compared with raw peanuts in a living mammal.
They suggest that: “A better understanding of how high-temperature antigen modification, such as peanut dry roasting, leads to allergic sensitisation should inform future preventive strategies, including those concerning early-age exposure, and therapeutic measures, such as the choice and route of antigen delivery in desensitisation strategies.”
This small animal study indicates that dry-roasted nuts and nut proteins cause a larger immune reaction than raw nuts. The team hypothesise that this might explain the difference between the prevalence of nut allergies in Western countries – where dry roasting is more common – and Eastern countries – where raw nuts are more typically consumed. While this study lends some weight to this idea, it does not directly prove it.
The study was consistent in its findings, giving them some validity, but we should consider that this was a small study involving mice. The findings are not directly applicable to humans, so we cannot say for sure that dry-roasted peanuts cause more allergic reactions or are the cause of the higher prevalence in the West – studies involving people would be needed to better explore this.
As the researchers acknowledge, further research confirming the findings of this study are required, which could include exploring ways to prevent allergies to nuts through desensitisation (immunotherapy). After these methods are developed in mice models, they might be investigated in humans. The path to a treatment or preventative strategy from this very early-stage research might be long and complex, so readers should not expect any immediate or short-term impact.
This research alone does not warrant the avoidance of dry-roasted nuts out of fear of developing a nut allergy. Similarly, if you have a history of nut allergies, you shouldn’t assume that raw, boiled or fried nuts will be safe to eat.
Those with an existing allergy should continue to take their normal action to prevent triggering their own allergy. Allergies can be very different in different people, so this might vary between individuals.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.