Some people with food allergies may not experience any obvious signs or symptoms
Food allergies are becoming more common around the world, and in some places, they are getting close to being an epidemic. Only in the U.S., do about 10% of children and adults have food allergies. The most common allergies are to cow’s milk, eggs, peanuts, and tree nuts. Some people have mild symptoms that might not need medical help, so these cases don’t get reported.
Food allergies, also known as food hypersensitivities, happen when the immune system overreacts to proteins in food that are usually safe. They can cause a wide range of symptoms, from itching, redness, and swelling in mild cases to vomiting, diarrhea, trouble breathing, and other symptoms that could be life-threatening in severe cases.
Patients can also be tested for food allergies by putting trace amounts of the offending proteins, called allergens, in their mouths or skin and watching how they react immediately. Doctors often use blood tests to measure how much immunoglobulin E, or IgE, is in the body. IgE is a special antibody that the immune system uses to find allergens and cause a response. Healthy people may have low amounts of IgE in their blood, but people with food allergies have much higher amounts, which makes them more likely to have severe allergic reactions.
But some people who show moderate increases in IgE on skin-prick allergy tests don’t have any allergy symptoms when they eat the allergen. This condition is also sometimes called “sensitization without symptoms.” People with this condition may not even know they have food hypersensitivity most of the time.
But are food allergies really without signs or symptoms? Or does it have effects on their bodies that they don’t know about?
As a health blogger, I study how food allergies change the brain. When I found out that some of my family members were allergic to cow’s milk, I became interested in this topic. Some people never eat dairy products at all because they have very bad symptoms that could kill them. People who don’t have typical allergic reactions sometimes eat dairy, but they get sick a day or two later for no obvious reason.
Researchers have found that if you’re hypersensitized, food allergens can affect your brain and behavior even if you don’t have typical food allergy symptoms.
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Behavioral disorders and food allergies are linked
Researchers have thought for decades that food hypersensitivities could be a cause of behavioral disorders. In 1949, a case report said that patients’ behavior and mood changed after they ate certain foods, like milk and eggs. After taking the suspected foods out of their diet, their symptoms got better, which suggests that food hypersensitivity was probably to blame. But it was interesting to me that the patients had been able to eat the foods that made them sick until they chose to stop. In other words, they were immune to the allergens even though they didn’t have any symptoms.
Several recent studies have shown a link between food allergies and depression, anxiety, attention-deficit/hyperactivity disorder (ADHD), and autism. They make it more likely that certain reactions to food allergens could involve the nervous system and show up as problems with how people act.
But the idea that food hypersensitivity can cause neuropsychiatric disorders is still debated because studies have come to different conclusions. Different types of allergies, ethnic backgrounds, eating habits, and other factors can lead to different results from the same study. More importantly, some studies included people who said they had food allergies but didn’t have lab tests to prove it, while others only included people with lab-proven food allergies. This meant that only people with symptoms could be looked into.
Food allergies, the brain, and how people act
One lab looked into whether food allergens could cause behavioral symptoms, especially in people who were sensitive but didn’t have any symptoms. They wanted to find out if eating the offending food could cause inflammation in the brain and changes in behavior after sensitization, even if there were no other obvious severe reactions.
They chose to work with mice to reduce the differences between people that come up in human studies. They made mice of the same age and genetic background sensitive to -lactoglobulin, or BLG, which is a common milk allergen, and then fed them the same food in the same room. They found that BLG-sensitized mice had slightly but significantly higher levels of IgE, but they did not react right away. Even though their IgE levels stayed high, they could eat food with the milk allergen in it for two weeks without showing any obvious symptoms. This showed that they were sensitive but didn’t have any symptoms.
Then they watched to see if their actions were still based on how they felt. They couldn’t ask mice how they felt, so they figured out what they were thinking by noticing changes in their normal, survival-focused behavior. Mice instinctively look around their environment for food and a safe place to live while avoiding danger. “Anxious” mice, on the other hand, tend to hide more to stay safe. They found mice that were “depressed” by holding them by the tail for a short time. Most mice will keep trying to get out of a bad situation, but sad mice will give up quickly.
Their experiments were meant to show what would happen if a person who was already sensitive to a food ate a lot of it in one day or small amounts of it every day for a few weeks. They imitated these situations by putting a lot of the milk allergen directly into the stomach of sensitized mice through a feeding tube or by giving them mouse food with the allergen in it so they could eat it slowly.
Mice that had been sensitized to BLG showed behavior like anxiety one day after getting a lot of the allergen. After eating small amounts of allergen for two weeks, another group of mice that had been sensitized showed signs of depression. Also, mice that had been exposed to BLG showed signs of brain inflammation and neuronal damage, which suggests that changes in the brain may be behind their behavioral symptoms.
They also looked at the long-term effects of eating allergens by giving BLG-sensitized mice a diet with allergens for one month. We found that the IgE levels of mice that had been sensitized went down by the end of the month. This shows that eating small amounts of the allergen over and over again led to less immune responses, or “desensitization.” On the other hand, there were still signs of brain inflammation, which shows that the harmful effects of allergens stayed in the brain.
Continuous brain swelling
Neuroinflammation, or long-term inflammation of the brain, has not yet been studied in people who are sensitized but don’t have any symptoms. In general, though, chronic neuroinflammation is known to contribute to neurodegenerative diseases like multiple sclerosis and Alzheimer’s disease, even though the exact causes of these diseases are unknown. Researchers can find out if food allergens can cause chronic inflammation that can lead to these diseases if they learn more about the role allergens play in neuroinflammation.
This information could be especially helpful for people who are getting allergy treatment through oral immunotherapy, which involves taking small amounts of allergens over time. The goal is to make the immune system less sensitive so that life-threatening allergic reactions, called anaphylaxis, happen less often. The U.S. The Food and Drug Administration has approved a standard form of peanut allergens to stop anaphylaxis in eligible children. But no one knows what it might do to the nervous system in the long run.
Food allergens can change the brain and behavior of people with no symptoms, making them neurologically not so asymptomatic. “You are what you eat” takes on a whole new meaning when you think about how your brain reacts to the food you eat.
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