A Q&A Guide to Understanding Food Allergies, Sensitivities & Testing

Millions of people struggle with symptoms like bloating, headaches, fatigue, skin problems, and digestive issues without realizing that the foods they eat every day may be contributing to the problem. In fact, research shows that 20% of people modify their diets because of adverse food reactions, yet many still never identify the true trigger.

This Q&A guide helps you understand the difference between food allergies, food sensitivities, and food intolerances, and how testing can help uncover hidden causes of your symptoms.

Q1: What’s the difference between a food allergy, sensitivity, and intolerance?

Food Allergy (IgE-mediated)

A food allergy is an immediate immune reaction involving IgE antibodies, often occurring within minutes of eating a trigger food. Symptoms may include:

  • Hives, swelling, itching

  • Wheezing or trouble breathing

  • Vomiting or diarrhea

  • Anaphylaxis (life-threatening)

The most common example is someone having an urgent severe peanut exposure reaction in which they need an emergency epinephrine dose (epi pen). These reactions occur when IgE antibodies bound to mast cells trigger a rapid release of histamine and other chemicals, causing classic allergy symptoms.

Food Sensitivity (IgG-mediated)

Food sensitivities involve IgG antibodies and produce a delayed Type III hypersensitivity reaction. Symptoms may appear hours, days, or even weeks later, making them difficult to trace.

IgG antibodies form immune complexes with food antigens; when the body cannot clear them, these complexes deposit in tissues and trigger inflammation, contributing to a wide range of symptoms.

Food sensitivities tend to be the most difficult for people to become aware because the of the delayed reaction. Honestly, can you remember what you had for lunch 5 days ago off the top of your head? You probably would have to have journal, right?

Food Intolerance (non-immune)

A food intolerance is not immune-mediated. It may result from enzyme deficiencies (e.g., lactose intolerance), chemical sensitivities, or difficulty digesting certain carbohydrates (FODMAPs). A common occurrence are intolerances for fatty foods, especially true for people who are having gallbladder or liver issues.

Q2: What symptoms might be caused by food sensitivities or allergies?

Common Symptoms of Food Sensitivities (IgG)

  • Digestive issues: bloating, constipation, diarrhea, gas, abdominal pain

  • Headaches or migraines

  • Brain fog, difficulty concentrating

  • Fatigue or chronic tiredness

  • Joint pain or stiffness

  • Skin conditions: eczema, psoriasis, hives

  • Mood disturbances: anxiety, irritability, depression

  • Respiratory symptoms: chronic sinus issues, asthma

  • Weight gain or difficulty losing weight

These symptoms tend to be delayed and chronic, worsening gradually as reactive foods continue to be consumed. Unfortunately for many patients they misunderstand that stopping these foods doesn’t necessarily produce immediate cessation of their symptoms, often it requires weeks or months. The misunderstanding can lead to confusion and question whether they have a food sensitivity or fearing it is something else.

Symptoms of Food Allergies (IgE)

  • Rapid onset hives, itching, swelling

  • Wheezing, coughing, shortness of breath

  • Vomiting or diarrhea

  • Anaphylaxis (life-threatening)

These occur immediately after consuming the food. Typically very easy for the patient to identify and understand which food caused the issue

Q3: Why do food sensitivities develop?

1. Increased intestinal permeability (“leaky gut”)

Damage to the intestinal lining allows partially digested food particles to enter the bloodstream, triggering an IgG immune response. This typically happens over time and can have a number of other factors that contribute, such as antibiotic use, food poisoning, gut infection (stomach flu), stress, alcohol, medications, nutrient deficiencies and auto-immune.

2. Loss of oral tolerance

Healthy immune systems “learn” not to react to foods. This process involves regulatory/suppressor T cells (TH3 cells) and production of TGF-β, which helps the body suppress unnecessary immune responses to foods. When tolerance fails, immune reactions emerge.

3. Frequent consumption of the same foods

Food sensitivities are most common to foods eaten daily because more immune complexes form with repetitive exposure. Every food is not pure, meaning there are always some elements within the food itself that the body doesn’t need. If the body doesn’t need it, it requires a process to eliminate it. These processes overtime can get overwhelmed triggering the immune system and symptoms (see answer to question 4).

Q4: How does IgG food sensitivity cause symptoms?

  1. IgG antibodies bind with reactive food antigens.

  2. Macrophages cannot clear all complexes when exposure is high.

  3. Excess immune complexes deposit in tissues.

  4. This causes Type III inflammatory reactions, contributing to symptoms in the gut, skin, joints, lungs, and brain.

Symptoms can persist weeks or months, even after removing the food, because IgG antibodies remain elevated for some time. This often can be confusing and frustrating for people, causing them to feel helpless and cause them to give up

Q5: How can testing help identify which foods are causing my symptoms?

1. IgE Allergy Testing (for immediate reactions)

Skin prick testing, RAST, or ImmunoCAP identify IgE-mediated allergies. These help diagnose immediate reactions such as peanut or shellfish allergies.

2. IgG Food Sensitivity Testing (for delayed reactions) aka “FST”

ELISA or microarray technology measures IgG antibodies, typically a range of 100–220 foods, identifying delayed reactions that contribute to IBS, migraines, skin issues, and more.

Studies show significant improvement when IgG-reactive foods are removed:

  • 76% saw symptom improvement

  • 68% saw benefits within 3 weeks

  • 92% had symptoms return when reactive foods were reintroduced

Supporting gut healing, proper detoxification of the gut and immune system can significantly reduce and remove reoccurrence of symptoms when offending foods are reintroduce in moderation or limited fashion.

It is important to understand the FST has limitations. It can have false positives and false negative results, obscuring a true understanding of which foods are affecting you. Clinically, the FST has about an 80% to 85% accuracy which provides a good guidance into launching into a optimize diet plan.

The final note on this test is timing. If there is chronic inflammation in the gut (hypersensitized immune system), there will be a lot of false positives with this test. It is best to get the inflammation controlled and then do the test.

3. Elimination and Challenge Diets (Optimizing Personal Diet)

The gold standard for confirming food reactions is the elimination and reintroduction food method, but often difficult and time-consuming to perform properly. Testing can guide which foods to eliminate first or set an agenda for the re-introduction of foods. Clinically, this is the most successful approach but does require time and dedication. 

This process starts with stripping down the diet to elemental or anti-inflammatory foods for 3 to 4 weeks, after which food or food groups are re-introduce according to a set agenda (FST, known or suspected foods or a list provided by your Naturopathic Doctor). Typically you would add them back one at a time, space out over 3 to 5 days so you can monitor how your body responds. Does it elicit a symptom over that period? This controlled reintroduction helps you clearly identify which foods are causing you problems. Ultimately, you will be able to design a tailored diet optimized for your body.

Q6: What conditions may improve by removing IgG-reactive foods?

Irritable Bowel Syndrome (IBS), A double-blind controlled trial showed significant reductions in IBS symptoms in patients who eliminated IgG-reactive foods compared to a sham diet.

Migraine Headaches, Removing IgG-reactive foods reduced the frequency of migraines and medication use. Reintroducing foods caused symptoms to return in 60% of patients.

Weight Management, Obese children and adults with elevated IgG antibodies showed improved inflammation markers, weight loss, and reduced waist/hip measurements when reactive foods were removed.

Skin Conditions, Mood Issues, Joint Pain & More, Improvements were seen in eczema, depression, anxiety, joint pain, and chronic fatigue after eliminating reactive foods (Box 15-1: Food Sensitivity Reactions).

Q7: What does a food sensitivity test report look like?

A typical report categorizes foods as:

  • Normal

  • Borderline

  • Elevated

This helps guide which foods should be eliminated and which are safe to include. Foods are often grouped into categories such as dairy, eggs, meats, grains, fruits, vegetables, nuts, seeds, and herbs/spices. To see a visual example, click here.

Q8: How long should I avoid reactive foods?

Ideal case is typically used in severe digestive distress cases, the Realistic case follows the 80/20 rule, gain 80% as quickly as possible to resolve the large majority, if not all the symptoms. Ultimately this is a good discussion as to what is right path for you with your Naturopathic Doctor.

Ideal case:

  • 4–6 months of elimination is recommended to allow IgG levels to drop and inflammation to resolve.

  • After this period, foods can be carefully reintroduced, typically every fifth day.

  • Some foods may need to be permanently avoided or severely limited if symptoms return.

Realistic case:

  • Most people improve after 3-4 weeks of avoiding certain foods, though gluten and dairy may need longer.  

  • Re-introducing foods using 3 day intervals, providing a more reasonable timeline

  • The large majority of foods can be re-introduced into the diet in limited fashion

Q9: Can food sensitivities ever resolve?

Absolutely! Once inflammation decreases and the gut heals, patients may tolerate reactive foods occasionally. However, chronic or repeated exposure may cause symptoms to return. 

People eventually learn the “price” (frequency and depth of reactivity) according to their decision of eating reactive foods. People can retake control of their diet, deciding when to eat liberally at important events such as a wedding. They'll recognize the consequences (symptoms) and, unless poor eating becomes a habit, can return to an optimal diet and restore gut health.

Conclusion: Are Your Symptoms Food-Related?

Food allergies, sensitivities, and intolerances often hide beneath chronic symptoms that seem unrelated to diet. Understanding the differences—and using the right testing—can help uncover the root cause of:

  • Digestive issues

  • Skin problems

  • Migraines

  • Fatigue

  • Mood imbalances

  • Weight changes

  • Chronic inflammation

If you’ve been struggling with persistent symptoms and haven’t found answers, food sensitivity may be a crucial next step. We can absolutely help you create and optimize a diet that works for your body!