Summary: Food allergens can affect your brain and behavior if you’re hypersensitized, even if you don’t have typical food allergy symptoms.
Source: The conversation
The prevalence of food allergies is increasing worldwide, to approach an epidemic level In certain regions. In the United States only, about 10% of children and adults suffer from food allergies, with allergies to cow’s milk, eggs, peanuts and tree nuts being the most common. Some patients have mild symptoms that may not require medical attention, leaving these cases unreported.
Food allergies, or food hypersensitivities, result from the immune system overreacting to usually harmless proteins in food. They can manifest as a range of symptomsranging from itching, redness and swelling for milder reactions, to vomiting, diarrhea, difficulty breathing and other life-threatening symptoms for severe reactions.
In addition to self-reporting, food allergies can be diagnosed by exposing patients to trace amounts of offending proteins, or allergens, via their mouth or skin and observe their immediate reactions. More commonly, doctors use blood tests to measure levels of immunoglobulin E or IgEa specialized antibody that the immune system uses to identify allergens and trigger a response.
Although healthy individuals may have low levels of IgE in their blood, patients with food allergies have much higher levels which increase their risk of having severe allergic reactions.
But some people who are positive in skin prick allergy tests with moderate increases in IgE do not notice any allergy-related symptoms when they eat the allergen. This condition is sometimes called asymptomatic sensitization. In many cases, people with this condition may not even be aware that they have a food hypersensitivity.
Are they really asymptomatic? Or are there effects in their body that they are unaware of?
I am a neuroscientist study how the brain is affected by food allergies. I became interested in this subject when I discovered that some members of my family had a hypersensitivity to cow’s milk. Some avoid dairy altogether because they have experienced severe and life-threatening symptoms. Those who don’t have typical allergic reactions eat dairy products occasionally, but seem to develop seemingly unrelated illnesses a day or two later.
What I and other researchers have found is that food allergens can affect your brain and behavior if you are hypersensitized, even if you don’t have typical food allergy symptoms.
Food allergies linked to behavioral disorders
Food sensitivities have been suspected by researchers for decades as a potential cause of behavioral disorders.
A 1949 case report described behavioral and mood disturbances in patients after eating certain foods, such as milk and eggs. Their symptoms improved after removing the suspect foods from their diet, suggesting food hypersensitivity was likely the culprit.
However, I was intrigued that patients could eat the offending foods until they chose to avoid them. In other words, they were asymptomatically sensitized, or tolerant, to allergens.
Several recent studies in humans have supported the association between food allergies and various neuropsychiatric disorders, including depression, anxiety, attention deficit/hyperactivity disorder and autism. They reinforce the possibility that certain reactions to food allergens may involve the nervous system and manifest themselves in behavioral disorders.
However, the idea of food hypersensitivity causing neuropsychiatric disorders is still controversial due to inconsistencies between studies. Differences in allergy types, ethnic backgrounds, dietary habits and other factors among study participants can produce conflicting results.
More importantly, some studies included people with self-reported food allergies, while others only included people with laboratory-confirmed food allergies. This limited investigations to only symptomatic individuals.
Food hypersensitivity, brain and behavior
My lab tested whether food allergens could manifest as behavioral symptoms, particularly in asymptomatically sensitized individuals. We wanted to know if eating offensive foods could lead to brain inflammation and behavioral changes after sensitization, even in the absence of other obvious severe reactions.
To minimize individual differences found in human studies, we decided to work with mice. We sensitized mice of the same age and genetic makeup to the common milk allergen, β-lactoglobulin, or BLG, and fed them the same diet in the same room.
We found that while BLG-sensitized mice produced moderately but significantly elevated levels of IgE, they did not show immediate allergic reactions.
They could even eat food containing the milk allergen for two weeks without showing any obvious symptoms, despite maintaining high IgE levels. This indicated that they were asymptomatically sensitized.
We then observed whether they showed any changes in their emotional behavior. Since we couldn’t ask the mice how they were feeling, we inferred their “feelings” by noting changes from their normal survival-oriented behavior. Mice instinctively explore their surroundings to seek food and shelter while avoiding potential dangers.
However, “anxious” mice tend to spend more time hiding to play it safe. We identified “depressed” mice by holding them briefly by the tail. Most mice will continue to fight their way out of this uncomfortable situation, while depressed mice quickly give up.
Our experiments were designed to simulate situations where asymptomatically sensitized individuals would eat either a large amount of an offending food in one day or small amounts every day for a few weeks.
We mimicked these situations by placing a large amount of the milk allergen directly into the stomachs of sensitized mice with a feeding tube, or by giving them allergen-containing mouse chow to eat the allergen a little at a time.
Interestingly, mice sensitized with BLG showed anxious behavior one day after receiving a large amount of allergen. Another group of sensitized mice developed depressive behavior after eating small amounts of allergens for two weeks.
Additionally, the BLG-sensitized mice showed signs of brain inflammation and neuronal damage, suggesting that changes in the brain may be responsible for their behavioral symptoms.
We also investigated long term effect of allergen consumption by keeping BLG-sensitized mice on the allergen-containing diet for one month. We found that IgE levels decreased in sensitized mice at the end of the month, indicating that continued consumption of small amounts of the allergen led to decreased immune responses, or “desensitization.” On the other hand, signs of brain inflammation remained, suggesting that the harmful effect of allergens persisted in the brain.
Chronic brain inflammation
Researchers have not yet studied prolonged brain inflammation, or neuroinflammation, in asymptomatically sensitized people. In general, however, chronic neuroinflammation is a known contributor to neurodegenerative diseases, such as multiple sclerosis and Alzheimer’s disease, although the exact causes of these diseases are unknown.
A better understanding of the role allergens play in neuroinflammation can help researchers determine whether food allergens trigger chronic inflammation that can lead to these diseases.
This knowledge could be particularly important for patients undergoing oral immunotherapyan approach to treating allergies that involves gradually ingesting small amounts of allergens over time.
The goal is to desensitize the immune system and reduce the incidence of anaphylaxis or life-threatening allergic reactions. In 2020, the US Food and Drug Administration approved a standardized form of peanut allergens to prevent anaphylaxis in eligible pediatric patients. However, its possible long-term effect on the nervous system is unknown.
Food allergens can affect the brains and behavior of seemingly asymptomatic people, making them less neurologically asymptomatic. Considering how your brain reacts to the food you eat gives a whole new meaning to the phrase “you are what you eat.”
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