The Sudden Onset of "Food Allergies" in Adulthood: The Threat Posed by Gut Health and Modern Lifestyle Creating a "Perfect Storm"

Chapter 1: What Exactly is "Food Allergy"?

1-1 The Mechanism of Food Allergies

Food allergies are diseases where the immune system mistakenly identifies proteins (allergens) in food as "enemies" and overreacts.

・Symptoms can occur even with a small intake
・It is often necessary to completely avoid the causative food
・Rarely, it can cause life-threatening anaphylaxis

These are some of its characteristics.

Symptoms are diverse, including itching, hives, swelling of the eyelids or lips, abdominal pain, vomiting, diarrhea, wheezing, difficulty breathing, low blood pressure, and impaired consciousness. Japanese data reports that about 10% of all food allergies involve shock symptoms (anaphylaxis).fujita-hu.ac.jp+1

1-2 From Childhood Illness to "Lifetime Risk"

In the traditional textbook image, it has been explained as follows:
・Onset occurs in infancy to early childhood
・Tolerance is acquired with growth
・Prevalence decreases in adults

In fact, some Japanese explanations estimate that "the prevalence of food allergies in adults is lower than in children, at about 1%."Japan Medical Journal

However, it is difficult to say "it's low, so it's safe." The type of food allergy that develops in adulthood has characteristics such as:
・Difficult to identify the cause
・Patients themselves may not suspect an allergy
・First noticed through severe anaphylaxis

Even in small numbers, these can lead to serious harm.

Chapter 2: The Global Increase in "Adult-Onset"

2-1 America: About Half of Adults Develop Allergies in Adulthood

According to a 2019 JAMA survey cited by Fox News, nearly half of adults with food allergies developed at least one food allergy in adulthood.Fox News+1

Additionally, an analysis by the allergy patient organization FARE (Food Allergy Research & Education) reported:
・Between 2007 and 2016, insurance claims for anaphylaxis due to food increased by about 377%
・More than one-third of these were adults aged 18 and over
・Anaphylaxis due to food additives and shellfish allergies is particularly common in adults

These findings have been reported.FoodAllergy.org

FAF estimates that "about 10% of American adults have some form of food allergy," with many believed to have developed in adulthood.FoodAllergy.org+1

2-2 Europe & Oceania: Emergence of New Allergens

In the UK, it is estimated that about 6% of adults have clinically confirmed food allergies.Food Standards Agency

Furthermore, French studies have reported an increase in adult anaphylaxis due to new foods not previously listed as major allergens, such as pine nuts, buckwheat, legumes, kiwi, apples, and bee products (honey and pollen).The Times

In Australia, while the prevalence of food allergies in adults is reported to be about 1 in 50, self-reported surveys in the US suggest that "1 in 10 adults has at least one food allergy."Hunter Medical Research Institute+1

2-3 Japan: From Infant-Centric to Unique Adult Allergies

In Japan, the prevalence of food allergies across all ages is estimated to be around 1-2%, with particularly high rates in infancy, and 1.3-4.5% after school age.foodallergy.jp+1

However, recent surveys and academic symposiums have reported:
・An increasing trend in the number of adult food allergy patients
・A rapid increase in demand for specialized medical care due to diverse pathologies and allergens
・Attention on "adult-specific" food allergies

These findings have been reported.Ministry of Health, Labour and Welfare Research Database+2CareNet.com+2

Examples include:
・"Food-dependent exercise-induced anaphylaxis" triggered by wheat + exercise
・"Pollen-food allergy syndrome (PFAS)" where people with birch pollen allergies experience oral itching from raw fruits like apples and peaches
These types of food allergies, which become more prominent in adulthood, are increasing.National Center for Child Health and Development+1

Chapter 3: Why Do Allergies Suddenly Develop in Adulthood?

Regarding adult-onset food allergies, it is not yet fully understood globally why they are increasing so much now. Fox News reports that a forum attended by the US Secretary of Health and Human Services (HHS), FDA Commissioner, and NIH (National Institutes of Health) Director discussed that "the cause is still not well understood."Fox News+1

Let's organize some of the factors currently considered influential.

3-1 Disruption of Gut Microbiota (Microbiome)

Dr. Makary, a top FDA physician, commented in a Fox News article:
"The gut contains billions of types of bacteria that maintain balance, but modern diets, antibiotics, and environmental factors can disrupt this balance, causing inflammation and potentially contributing to food allergies."
Fox News+1

・Western-style high-fat, high-sugar diets low in dietary fiber
・Frequent use of processed foods and additives
・Repeated use of antibiotics

These are pointed out as factors that reduce the diversity of gut bacteria, leading to an imbalance in the immune system and causing overreactions to previously harmless foods.CDC+1

3-2 Hygiene Hypothesis and "Too Clean" Environments

In modernized countries, infectious diseases and parasites have decreased, and living environments have become cleaner. While this seems beneficial, it is suggested that a lack of "moderate exposure to bacteria and parasites" in childhood may lead to an immune system that "does not get used to external threats as it grows into adulthood."Ministry of Health, Labour and Welfare+1

As a result,
・Overreacting to otherwise harmless foods or pollen
・The immune system attacking itself or harmless substances

This is the "hygiene hypothesis," suggesting an increase in allergic tendencies.

3-3 Environmental Chemicals and Air Pollution

・Microplastics
・Pesticides
・Preservatives and additives
・Exhaust gases and PM2.5

These modern life chemicals and air pollutants are also thought to affect the immune system. While not many specific substances have been identified as causes, the timing of the overall increase in allergic diseases and environmental changes coincides, leading more experts to see it as "multiple factors accumulating and manifesting as food allergies."PMC+1

3-4 Changes in Diet and "New Ingredients"

・The normalization of nuts (walnuts, cashews, pistachios, etc.)
・The rapid spread of plant-based milk and high-protein plant foods (pea protein, lentils, etc.)
・Diversification of imported foods and ethnic cuisine

These changes have increased opportunities to consume "ingredients that were not commonly eaten before." French research has shown that these "newcomer" ingredients are a factor in adult anaphylaxis, calling for a review of Europe's allergen labeling list.The Times+1

In Japan, there is an increase in shock cases due to tree nuts like walnuts and cashews, with recent surveys reporting walnuts as one of the top causative foods.Consumer Affairs Agency+1

Chapter 4: Common Allergens in Adults: Differences Between the World and Japan

4-1 Notable Allergens in America and Europe

Common allergens for "new onset" in adults include:
・Shellfish (shrimp, crab, lobster, etc.)
・Tree nuts (walnuts