How To Read Food Intolerance Test Report: Levels, Colors & Meaning

A food intolerance test report serves as a practical guide rather than a permanent food restriction list. It uses laboratory methods to identify immune responses to specific foods. By understanding IgG levels and color-coded results, you can identify foods that may be triggering delayed symptoms.

Receiving a food intolerance test report can initially feel confusing. You will be introduced to a very long list of common foods, some of which are red, others are yellow or green.

Many reports fail to clearly explain what the results mean for your health. You are not alone if you do not know how to interpret the food intolerance test results.

Most modern food intolerance tests measure food-specific IgG (Immunoglobulin G) antibodies linked to delayed immune reactions. The test measures IgG antibodies produced by your immune system in response to specific foods.

These antibodies are linked to delayed reactions that can occur hours or even days after eating.

These reactions are quite different compared to the classic food allergies that are tested using the IgE (Immunoglobulin E) antibodies. An allergy test, such as a skin test or a blood test for IgE antibodies, is designed to detect IgE-mediated allergies, which cause immediate and sometimes severe reactions like hives or anaphylaxis.

IgG-mediated reactions typically develop hours or even days after eating the food. The symptoms are commonly associated with bloating, headaches, joint pain, skin problems, fatigue, or brain fog. Repeated exposure to certain food components can contribute to chronic inflammation and long-term health issues.

Most laboratories adopt the use of a traffic-light color system to make interpretation easy. This visual system allows you to quickly identify potential trigger foods. Ongoing exposure to certain food components can contribute to chronic inflammation, which may lead to persistent health issues.

The test can also help identify specific food components, such as proteins or other elements within foods, that may be responsible for triggering immune responses.

It shows elevated food-specific IgG antibodies, which may indicate immune recognition and possible sensitivity when correlated with symptoms. It indicates specific foods that most probably cause symptoms. A red-zone result indicates that your immune system has produced high levels of IgG antibodies against a specific food protein.

What it means

Your body is now sensitized towards this food. The immune system actively reacts to the offending food, which can lead to ongoing low-grade inflammation.

It is possible that recurring exposure is maintaining your immune system in a chronic and low-grade inflammatory state, which leads to chronic symptoms. Unlike food allergies, which cause immediate and severe reactions such as hives or anaphylaxis, food intolerances usually cause delayed and milder symptoms.

Common culprits

Some of the dietary staples found in red-zone foods are:

• Dairy products

• Gluten-containing grains

• Eggs

• Soy

• Certain nuts or legumes

These foods are usually eaten, and this raises the possibility of overexposing the immune system.

Next steps

Most functional medicine practitioners prescribe 3-6 months of total abstinence from red-zone foods. This rest period gives the gut lining time to repair and the immune system time to down-regulate. After this period, you can cautiously reintroduce foods while monitoring symptom improvement.

This result indicates a moderate immune response. Demonstrates an average immune response. It indicates certain foods that can be problematic when consumed regularly or when they are combined with other trigger foods.

The Yellow-zone outcomes are moderately elevated IgG levels, suggesting a partial or emerging immune response.

What it means

These foods do not always cause symptoms when you eat them. However, moderate immune responses may occur to particular foods.

Consuming these foods together or frequently can make symptoms worse. They have the potential to add to the so-called ‘toxic bucket’ effect described by practitioners.

Next steps

Medical and allergy organisations do not universally accept IgG food testing as a diagnostic tool for food intolerance. This implies that one should consume yellow-zone foods not more than three to four times a week.

The green zone shows a mild or normal reaction. Represents low IgG activity. The immune system is generally well-tolerant of these foods.

The grey zone usually represents borderline or inconclusive reactions rather than true negatives. It indicates the foods that are unlikely to cause symptoms and are related to the immune system.

What it means

Such foods are not likely to cause the symptoms of immune-mediated food intolerance and can usually be consumed regularly in the diet.

Important note

IgG testing does not measure:

• Lactose intolerance

• Lactase deficiency

• Fructose malabsorption

• Histamine intolerance

• Food allergy or allergy to chemicals

In cases where true allergy is suspected but IgG testing is negative, oral food challenges may be used alongside other diagnostic methods, such as medical history, physical examination, skin prick testing, and food-specific IgE levels, to confirm food allergies.

Even when a food appears in the green zone, individual symptoms should always guide decisions. If symptoms consistently return following the consumption of a green-zone food, then non-immune intolerance might be linked.

Note: IgG food testing is not universally accepted as a diagnostic test for food intolerance. Many professional allergy organisations consider IgG antibodies to reflect food exposure rather than disease. For this reason, IgG results should never be used alone to diagnose food intolerance but rather as a guide alongside symptom tracking and professional evaluation.

Most food intolerance test reports, in addition to color coding, give numerical values of the IgG antibody levels, usually in IU/ml (International Units per milliliter). These figures are the measurements of the degree of immune response to certain food proteins.

The larger the value of IU/ml, the stronger the source of immune recognition is at the time. Elevated levels can help identify potential food triggers that may be contributing to symptoms such as digestive issues, migraines, skin conditions, or inflammation.

The adaptive immune response of the body contains IgG antibodies. Increased intestinal permeability may allow larger food protein fragments to cross the gut barrier in some individuals.

No standard normal IgG level for food intolerance testing exists. Each laboratory sets its own reference ranges depending on its test procedure, antigen preparation and population data.

In most reports:

• Low or Negative: A value that falls below a predetermined cutoff (usually at or below 7.5 IU/ml) is considered negative or clinically insignificant

• Moderate: The mid-range values are in a moderate or yellow range

• High: The values that are higher than the upper threshold are considered as high or red-zone reactions

Due to reference ranges, it is necessary to put the numbers in the context of the color coding used by the lab, not to compare the values of various testing providers.

The most frequent misconception is that the greater the number of IU/ml, the worse the symptoms. Actually, the IgG level is not an ideal correlate of the intensity of the symptoms.

• There are those with high IgG levels and few symptoms, particularly when the nervous system and detox pathways are strong.

• Others develop considerable symptoms even with moderate or even low levels of IgG, especially when they are exposed to more than one trigger or are inflamed. These individuals may experience symptoms across multiple body systems, including migraines, asthma, anxiety, or chronic fatigue.

IgG is an indication of immune recognition, not an expression of the symptoms. The symptoms are based on numerous other factors, such as gut health, stress, hormonal balance, microbial diversity, and the total inflammatory burden.

Learning about your food intolerance report is not the end. The difference between the real and the ideal is the way you use the results in your real life.

The IgG food intolerance test is not a matter of forever exclusion of foods when done in a proper manner. It is a matter of pattern determination, reduction of immune stress and development of tolerance with time.

Identifying and managing food triggers can help alleviate digestive issues, such as bloating, diarrhea, and stomach discomfort, which are commonly associated with food intolerances.

Pause and relate your test results to your real-life experience before getting rid of anything. Examine the foods to know:

• Do I consume these foods on a daily basis or several times a week?

• Do my symptoms get worse after eating these types of foods?

• Do these foods make up my healthy staples?

Reactive foods are often consumed frequently. This repeated exposure keeps the immune system activated and sustains symptoms. Test results are much more likely to cause bloating, fatigue, headaches, skin problems, or digestive distress.

Digestive problems such as bloating, gas, or stomach pain are common symptoms to watch for when correlating test results with your experience. This action assists one in focusing on what is to be addressed initially rather than doing everything at once.

The elimination phase aims to reduce immune stimulation and allow the gut lining to recover.

During this phase:

• Eliminate high-IgG (red-zone) foods entirely

• Minimize or provisional cutback of moderate (yellow-zone) foods, based on the severity of symptoms

• Focus on simple, whole, anti-inflammatory foods

Most of the practitioners suggest that the elimination should take no less than 4 weeks, and that will give the inflammatory signals time to calm down and symptoms to get better. At this period, foods that promote gut integrity should be of primary importance, including fibre-rich vegetables, high-quality proteins, healthy fats, and proper hydration.

The reintroduction phase starts when the symptoms are improved or stabilized. This is a very important step that is not taken seriously, but it is the most valuable insight.

Reintroduce foods:

• One at a time

• In a small portion on day one

• Space between tests of two or three days

Keep an eye on both digestive and non-digestive symptoms such as stomach pain, fatigue, headaches, joint pain, mood changes or skin reactions. Stomach pain is a key digestive symptom to watch for, as it may indicate a food intolerance. In case of a recurrence of the symptoms, then that food is probably a true trigger and must be avoided over a more extended time.

This step helps differentiate true food intolerances from foods that appeared reactive due to temporary gut inflammation or overexposure.

Although self-elimination may be effective, a qualified nutritionist or functional health practitioner can help to make the process safe and effective.

Professional advice is useful in:

• Nutritional adequacy, particularly in the case of numerous foods being eliminated

• Planning of a balanced meal to avoid deficiencies or overrestriction

• Planned reintroduction, decreasing avoidance of food and unwarranted avoidance in the long term

A healthcare provider can also assist in determining underlying causes of gut infections, stress, or enzyme deficiencies, which may be causing food sensitivities in the first place. They provide the best suggestions for your overall well-being.