LTP allergy: what you can and cannot eat

What is LTP and why does it cause allergies?

LTP (short for lipid transfer protein) is a protein plants use to defend themselves against microbes, extreme heat and drought [2]. It is found only in the plant kingdom. Meat, fish, eggs and dairy products do not contain it.

Two features make it a difficult allergen. First, it is resilient. Its structure, held together by four disulfide bonds, withstands heat and digestion, so it remains present in raw, cooked and processed foods [2]. Second, it is very similar from one plant to another. The four main sites recognised by the immune system in peach LTP are the same in other related fruits [2]. As a result, an allergy that starts with one fruit can end up affecting very different foods.

Which foods contain LTP?

Many, which is why a general list is of little use. LTP has been identified in stone and pome fruits (peach, apricot, plum, cherry, apple and pear), as well as in strawberry, grape, kiwi, citrus fruits, pomegranate and blackberry [2]. It is also found in tomato, lettuce, cabbage, cauliflower, broccoli, asparagus, celery and carrot, and in wheat, maize and rice [2]. It is found in almonds, hazelnuts, walnuts, chestnuts and sunflower seeds; lentils, beans, peanuts and soy; and mustard, flaxseed and other seeds [2].

What matters is the difference between being sensitised, meaning a test comes back positive, and reacting when you eat the food. Across seventeen allergy clinics in Italy, the 210 people who were sensitised reported reactions mainly to peach (85 %), apple (35 %) and nuts (20 %) [2]. By contrast, most reported no reaction to lentils, soy, maize or sesame, even though tests were positive for LTP in those foods [2].

Do you need to avoid all foods that contain LTP?

No. Avoid the food you are allergic to and keep eating the foods you tolerate. These are the first two recommendations in the European food allergy guideline, and both carry strong recommendations [1]. The second is there precisely because the first is applied too broadly.

Advice needs to be tailored to each person to prevent many foods being excluded at once [4]. What to remove and what to keep depends on your clinical history and test results. A positive test for an LTP allergen only confirms the diagnosis when it is accompanied by a typical clinical history [4].

Doing the opposite has a cost. Unsupervised avoidance diets that are continued for too long increase the risk of nutritional deficiencies [1]. This is where we come in. The same guideline recommends individualised dietary advice, with support from a dietitian-nutritionist in complex cases [1]. This is how we work in our allergy and intolerance dietitian-nutritionist consultation.

Does peeling or cooking fruit help?

It can help to some extent, and it is useful to know why. LTP is concentrated in the outer layers of plants. In peaches, the amount of Pru p 3 (the technical name for its LTP) is high in the skin. In walnuts and hazelnuts, it accumulates in the brown skin around the seed [2]. Removing the skin therefore reduces the amount of protein that reaches your plate .

Reducing it does not remove it. LTP withstands heat and processing, so it remains present in cooked and processed foods [4]. In UK data, reported triggers included prepared dishes such as pizza or curry [4]. An allergy specialist will decide whether peeling or cooking is enough in your case, almost always with a controlled food challenge .

Why do I react sometimes but not others?

Because of cofactors, the question we hear most often in consultations. Many of these reactions may need a cofactor for the food to trigger them, such as exercise, alcohol, anti-inflammatory medicines or cannabis [3]. The same peach that caused no problem yesterday may trigger a reaction today if you eat it before going for a run.

Severe reactions, including anaphylaxis, are not uncommon with this allergy and are often facilitated by exercise or alcohol [4]. So, when you eat something you are not entirely sure about, avoid strenuous exercise and alcohol, including beer and wine. No amount of alcohol is safe for health (WHO): the less, the better. Avoid it completely during pregnancy and breastfeeding, in childhood, if you are going to drive, or if your medication does not allow it. If you take anti-inflammatory medicines often, discuss this with your doctor .

What is LTP syndrome?

LTP syndrome is the term for the condition when the allergy affects several plant foods at once, whether related or not, because their LTPs are similar [2]. It is the same allergy involving more foods. In the Mediterranean basin, it is an important cause of food allergy in adults. It accounts for a large proportion, perhaps the largest, of food-related anaphylaxis [2].

Giving the condition its own name does not change the advice. Avoid what has caused a reaction and whatever the allergy specialist recommends, and keep everything else in your diet. What does change is the care needed when planning your shopping, because the more foods you have to avoid, the easier it is to miss something.

How to order at a restaurant

Name the specific foods. “I have an LTP allergy” does not tell the kitchen much. “I cannot eat peach, apple or nuts, including in sauces or desserts” is clear straight away. Also ask about dressings and side dishes, where these ingredients can slip in.

The fruits and vegetables that most often cause reactions are not among the fourteen allergens that must be declared. Neither the menu nor the label will alert you to them, so you need to ask.

What mistakes do we see most often in consultations?

Removing the whole list on day one. It comes from the shock and is understandable, but in three months it leaves a diet of ten foods. Avoid what caused a reaction, and keep eating the rest unless your allergy specialist advises otherwise.

Checking at home whether you can tolerate a food again. With an allergy that carries a risk of anaphylaxis, a food is reintroduced in hospital, with the necessary medical resources . At home, the only thing you are testing is your luck.

Not reviewing the diagnosis. Some people have avoided fifteen foods for years based on old test results. The avoidance diet should be reviewed with an allergy specialist, and it is common to be able to bring some foods back. If, over time, the main problems are bloating and digestive discomfort rather than reactions, it is worth looking at another explanation. For example, it could be sorbitol intolerance, involving a sugar found in many fruits.