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Why Would My Patient Have a Positive Food Sensitivity or Allergy if They Haven't Eaten That Food?

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Why Would My Patient Have a Positive Food Sensitivity or Allergy if They Haven't Eaten That Food?

True food allergies are when the body develops antigens against a particular or related food. Patients can be sensitive to food, they can be allergic, or they can be reactive in a different way. Sometimes patients will be surprised by a food antigen test result when a food they don’t eat shows up as positive for one of the allergic markers on the test. 

How can that be? Since a food allergy requires antigen development, then how would antigens develop if the food isn't consumed in the first place? There are several reasons. 

This article will explore food allergies and sensitivities, how the body makes antigens, and what food and/or environmental exposures can activate these antigens. 


Ruling Out Labeled Allergens

When a patient reacts to food, the first thing that should be done is to rule out that a hidden allergen isn't present in the patient's diet. 

Sometimes patients will consume foods they don't realize they are ingesting. A good example might be ingredients found in packaged foods as stabilizers, emulsifiers, thickening agents, and preservatives. Some examples include cornstarch, carrageenan (extracted from algae/moss), tapioca, arrowroot, guar gum, and gelatin. 

There are also ingredients that patients might need to be made aware of are standard components of some foods, such as gluten from wheat in soy sauce, anchovy in Worcestershire sauce, and insect and plant sources for food colorings. Interview the patient about sauces and flavorings they may use and encourage them to carefully read labels to rule out the possibility of an allergen they may not be aware of.

Ruling Out Hidden Allergens

A second possibility beyond a patient simply eating a labeled allergen without awareness is that they could be consuming hidden allergens. Hidden allergens are different from labeled allergens because a patient won't be able to tell from a label that the food is there, so it can be easier to miss. Dining out is particularly difficult when trying to parse out which allergens are present. Some restaurants are fantastic in providing allergen information, while others may need to be better informed or better communicate the data. Even restaurants that note specific allergens can still make mistakes. For example, a restaurant may not have a dedicated grill or fryer for different foods leading to cross-contamination. 

Outside the restaurant environment, packaged foods may have been processed on machinery that also processes an allergen. Certain hidden additives do not have to be reported on a label if used in small amounts under US or EEC guidelines. 

Common "hidden" allergens include mustard, celery, spices, lupine, pea, natural food colorings, and preservatives, but can occasionally include allergenic material from contaminants such as cereal mites." (1

Ruling Out Cross-Reactivity Between Foods In The Same Family

A third possibility is a cross-reactivity between foods in the same family. Foods are grouped into food families because they are taxonomy-related and share the capacity to cross-react in creating antibodies. Although this might be confusing in the sense that the test shows a food that isn't normally consumed as reactive, in fact, it's an opportunity for more effective treatment. After a positive food antigen test result, the standard of care is to place the patient on an elimination diet, where foods reacted to are eliminated and gradually introduced. 

Foods in the same family that can be cross-reactive are also recommended to be eliminated so that a complete chance for improvement is possible. It's better to cast a wider net- as long as that net is based on comprehensive testing that can offer guidelines for elimination based on an intersection of markers. 

Gluten or Wheat Allergy

A gluten or wheat allergy is one of the more important results that can be delivered. It's most likely that both gluten and wheat will show up together as positive if either does. Sometimes, a patient may test positive for gluten but not wheat or vice versa. Wheat contains gluten, but gluten comes from many other grains as well. If gluten shows up but wheat doesn't, the patient may not have consumed wheat, so the cross-reactivity isn't that strong. If wheat shows up, but gluten doesn't, then it's more likely that the patient is reacting to other compounds in the wheat. 

Mold Allergy 

Mold positivity could be cross-reactivity with cheeses that contain mold, peanuts, melons, sake, vinegar, kombucha, alcohol, soured breads, fermented foods, cider, rootbeer, pickled and smoked meats, dried fruits, canned tomatoes, and canned juices. 

Why? Sometimes because the mold has contaminated the food (dried fruit and tomatoes rarely are completely mold-free), and sometimes because specialized molds are used on purpose to ferment the foods (like kombucha, sake, and soured foods). 

Yeast positivity can be possible because a patient is infected with Candida. Take a look at the chart and see how related foods can cross-trigger as well. Examples include almonds with peaches, asparagus with garlic or onions, avocados with cinnamon, cacao with kola nut, spinach with quinoa, etc. 

Other Reasons For Reactions

Sometimes, a specific food won't appear on the test as an allergen or sensitivity when a patient knows they are reactive. There are several possible reasons for this as well. Foods high in histamines (like smoked meats, cheeses, etc.) can cause a direct reaction to the histamines in the food rather than an allergic reaction to the food itself. Likewise, foods like smoked meats can be high in nitrates and nitrites. Wine can be high in sulfites, etc. 

These chemical reactions are not allergic reactions to the foods themselves, and when an allergy doesn't show up, it can steer the patient to continue to consume meats and wines, for example. 

There can be non-allergic reactions to gluten because gluten interferes with the ability to convert amino acids into neurotransmitters. Specific foods might cause a platelet-activating factor- not an allergy, but a noticeable reaction. Depending on the patient, other foods may be high FODMAP. The P88 Dietary Antigen Test is a powerful tool for diagnosis, but like other valuable tools, sometimes it may just rule out a pathway.

Ruling Out Cross-Reactivity To An Environmental Allergen

The fourth possibility as to why a food that the patient doesn’t consume may still show up in the results of a food antigen test is because of cross-reactivity to an environmental (often airborne) allergen.

Some of these allergens are very interesting. For instance, someone who shows up as allergic to beef but is a vegetarian might be disbelieving. It turns out that beef allergies cross-react with tick allergies. In fact, someone who doesn't eat beef and tests positive for that food allergy should be examined for Lyme disease symptoms. 

Patients who don't eat seafood but test positive for clams may cross-react with an allergy to roaches. 

Latex is cross-reactive to bananas and a host of other foods. Meat allergies can be cross-reactive to animal dander. Many pollens can cross-react with fruits and vegetables. 

Maple syrup and barrel-aged products (including alcohol) may cross-react with the pollen from the trees used to age them (an ongoing area of research that is sometimes hotly disputed by the wine and spirits industry). It's wise to consider the environmental interplay when a specific food is tested as positive for a patient who says they don't consume that food.

The Physician's Guide to the P88 Food Antigen Test contains a chart showing potential environmental and food allergens interactions. 

Testing for Food Allergens and Cross-Reactivity 

The Precision Point Diagnostics P88 Dietary Antigen Test evaluates all foods for IgE, IgG, IgG4, and C3d reactions. The 88 foods on the test were chosen to represent a spectrum of foods common in the diet to have the most comprehensive usefulness to the clinician. In addition, the range of foods on the panel can be an excellent tool for picking up some foods that do not appear. Various food groups can show cross-reactivity with each other, allowing the clinician to consider foods outside the panel's scope.

This allows the physician to decide which food groups should be focused on for entire elimination (particularly those associated with a high C3d result indicating systemic inflammation and a low IgG4 reaction meaning little alleviation of inflammation through that response) and which food groups can be ignored altogether or only partially decreased in the elimination diet. 

As individual foods are reintroduced, the family cross-reactivity is zeroed in for that patient. 

Precision Point Diagnostics also offers a free physician's guide to the  P88 Dietary Antigen Test that not only describes the test in full and how to interpret it but also contains comprehensive tables on foods that are cross-reactive classified in groups, as well as a table on the interaction between specific environmental allergens and which foods they can interact with. 

Although you'll find a complete list of cross-reactive foods in the Physician's Guide tables, let's look at some of the interactions that might be of particular interest. 


Food antigen testing is a complicated business because of the complexity of the pathways whereby food allergies are formed. Knowing the interplay of foods with each other, foods with the environment, hidden food allergens, and the types of allergic reactions can make a more successful physician when treating your patients. Food allergies are as diverse as the patient, and this is why simple food tests that don't allow for the interactions between different pathways for allergic reaction don’t tell the whole story. Elimination diets can be challenging to get patients to comply with. The more compelling you can be with your explanations to them, the greater the degree of success you are likely to have. 

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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