Written by Hannah Hunter, Specialist Allergy Dietitian
When people think about food allergy, the first foods that typically spring to mind include peanuts, milk, eggs and fish. It may therefore surprise many to hear that fruits and vegetables are the top foods responsible for food allergy in adults (1 - see references below article).
Whilst egg and milk allergy are more common in children (2), these are usually outgrown by adulthood (3) (4), when we see different patterns of food allergy emerge (5).
Pollen food syndrome
The most common form of allergy involving plant foods is known as pollen food syndrome (PFS) or oral allergy syndrome (OAS).
PFS affects approximately 2% of UK adults (1) and is related to an allergy to pollen, usually birch (6). Most people will also have springtime hayfever, although this is not always present. Plant foods such as apples contain similar proteins to those found in pollens and when uncooked versions of these foods are consumed by people with PFS an allergic reaction occurs, known as a crossreaction. Symptoms usually just affect the mouth and throat and consist of itching and local swelling.
Which foods are involved?
- PFS can be triggered by a variety of plant foods in their raw form:
- Fruits – apple, pear, cherry, peaches, plums, strawberry, kiwi
- Vegetables – carrots, celery, tomato, beansprouts
- Nuts – hazelnuts, almonds, brazil nuts, walnuts. It is also common for people to get itchy hands when handling raw fruits or vegetables, particularly when peeling potatoes
How can you recognise PFS?
A useful questionnaire and algorithm has been developed and validated to recognise PFS7 to provide appropriate advice.
Based on this algorithm, a diagnosis of PFS can be made without further testing if the following features are present:
- Symptoms of hayfever (March-May)
- Reactions occur with fruit, vegetables, nuts or herbs
- Reactions to raw but not cooked fruit and vegetables or when peeling fruits or vegetables
- Symptoms occur on biting, chewing, swallowing or less than five minutes after eating
- Usual symptoms of mild-moderate tingling, itching, soreness or angioedema of the oropharynx or throat
Practical advice for PFS
1. Avoid the foods that cause symptoms – most people will do this automatically since the symptoms are unpleasant. Fresh smoothies and raw juices should also be avoided as these can contain large amounts of the allergenic proteins.
2. Find alternatives – although it is common to react to different raw fruits, vegetables or nuts, there are usually a number of other plant foods that people will be able to eat without symptoms.
3. Choose cooked or tinned versions – the proteins involved in PFS are denatured by heat6 so cooking or pasteurising usually renders the foods safe. Most reactions are mild and are relieved with an antihistamine tablet and by drinking water.
The BDA's Food Allergy Specialist Group has developed a comprehensive diet sheet on PFS
Can PFS be severe?
Although in most cases symptoms are mild and resolve quickly, a small number of people develop more severe reactions due to PFS.
These individuals may need to carry an adrenaline pen (e.g. Epipen or Jext) and should be assessed by an allergy specialist (8). Severe reactions have also been reported in people who consume large amounts of the foods they react to (9).
This is why it is important to avoid raw juices and smoothies that contain fruits and vegetables that usually provoke PFS symptoms. Advice from a dietitian regarding this is beneficial. People with PFS can also have reactions that range from mild to severe to soya milk, in which the proteins involved are present in large amounts despite processing (10). People who react to soya milk usually tolerate other soya foods such as tofu and soy sauce.
Lipid transfer protein (LTP) allergy
Other severe reactions to fruits and vegetables can occur due to LTP allergy (11). LTPs are small proteins found in a wide variety of plant foods; common foods include tomatoes, apples, raspberries, stoned fruit, grapes, walnuts, almonds, corn and barley.
Patients may react to one or multiple foods. The allergens are not destroyed by heat and are therefore present in cooked and processed foods, including wine and beer. Reactions are often associated or exacerbated by exercise or alcohol consumption and therefore may be delayed or inconsistent. A diagnosis of LTP allergy should be made by an experienced allergy specialist supported by a dietitian, as these foods are not covered by the current labelling law.
When should someone be referred to an allergy clinic?
If a diagnosis of PFS is clear, they may not require referral for a specialist allergy assessment and can be managed using the above advice. There are three scenarios when referral to an appropriate allergy clinic should be made:
1. Following severe reactions or anaphylaxis: If a patient has developed systemic symptoms after eating fruits or vegetables, such as rashes, severe swelling, vomiting, difficulty breathing, or collapse, they require further investigations as they may not have PFS or may need to carry an adrenaline pen.
2. Reactions to nuts: It can be difficult to distinguish PFS from primary nut allergy when people react to nuts, especially as the cross reactive proteins are present in both the raw and cooked forms of nuts.
3. Reactions occur with cooked fruit or vegetables: In this instance, PFS is unlikely and the individual may have another form of food allergy, such as to LTPs.
- Skypala I.J., Bull S., Deegan K., GruffyddJones K., Holmes S., Small I., et al. prevalence of PFS and prevalence and characteristics of reported food allergy; a survey of UK adults aged 18-75 incorporating a validated PFS diagnostic questionnaire. Clinical and Experimental Allergy. 2013;43(8): 928-940.
- Venter, C., et al., Prevalence and cumulative incidence of food hypersensitivity in the first 3 years of life. Allergy, 2008. 63(3): p. 354-359.
- Santos, A., A. Dias, and J.A. Pinheiro, Predictive factors for the persistence of cow’s milk allergy. Pediatr Allergy Immunol, 2010. 21(8): p. 1127-1134
- Allen, C.W., A.S. Kemp, and D.E. Campbell, Dietary advice, dietary adherence and the acquisition of tolerance in egg-allergic children: a 5-yr follow-up. Pediatr Allergy Immunol, 2009. 20(3): p. 213-218.
- Ker, J. and T.V. Hartert, The atopic march: what’s the evidence? Ann.Allergy Asthma Immunol., 2009. 103(4): p. 282-289.
- Andersen M.B., Hall S., Dragsted LO. Identification of european allergy patterns to the allergen families PR10, LTP, and profilin from Rosaceae fruits. Clinical reviews in allergy & immunology. 2011;41(1): 4-19
- Skypala I.J., Calderon M.A., Leeds A.R., Emery P., Till S.J., Durham SR. Development and validation of a structured questionnaire for the diagnosis of oral allergy syndrome in subjects with seasonal allergic rhinitis during the UK birch pollen season. Clinical and Experimental Allergy. 2011;41(7): 1001-1011.
- Katelaris CH. Should patients with pollen fruit syndrome be prescribed an automatic epinephrine injector?. Current Opinion in Allergy and Clinical Immunology. 2016;16(4): 370-374.
- Roseler S., Balakirski G., Plange J., Wurpts G., Baron J.M., Megahed M., et al. Anaphylaxis to PR-10 proteins (Bet v1 homologues). Hautarzt. 2013;64(12): 890-892.
- Treudler R., Werner M., Thiery J., Kramer S., Gebhardt C., Averbeck M., et al. High risk of immediatetype reactions to soy drinks in 50 patients with birch pollinosis. Journal of Investigational Allergology and Clinical Immunology. 2008;18(6): 483-484.
- Asero R, Mistrello G, Roncarolo D, Amato S. Relationship between peach lipid transfer protein specific IgE levels and hypersensitivity to non-Rosaceae vegetable foods in patients allergic to lipid transfer protein. Annals of Allergy, Asthma and Immunology. 2004;92(2): 268-272.