Food Intolerance: How to Identify, Treat, and Improve Quality of Life

Have you ever felt discomfort after eating certain foods, such as bloating, abdominal pain, or even fatigue? These symptoms may indicate food intolerance, a common condition that affects millions of people worldwide. 

It is estimated that up to 20% of the population suffers from some type of food intolerance, but many people go years without a proper diagnosis. Recognizing the signs and getting the right test can be the key to improving quality of life. After all, understanding what your body needs (or does not tolerate) is essential for a balanced and discomfort-free diet! 

In this article, we will explore the difference between food intolerance and food allergy, the main foods that can trigger the condition, the diagnostic process, and the primary tests used to determine the best therapeutic approach for food intolerance. Enjoy your reading!

What is Food Intolerance? 

Food intolerance or sensitivity encompasses different definitions and is generally characterized as an adverse reaction to food without direct involvement of the immune system. 

This condition may be related to a deficiency of digestive enzymes, as in lactose intolerance, or to a delayed inflammatory response mediated by immunoglobulin G (IgG) (1,2). 

When there is a deficiency of enzymes responsible for digesting certain foods, their metabolism becomes incomplete, leading to uncomfortable gastrointestinal symptoms. 

Additionally, another suggested mechanism involves increased intestinal permeability, which may allow food antigens to enter circulation, stimulating the production of specific IgG against food proteins (3). 

This phenomenon is associated with reduced levels of anti-inflammatory cytokines, such as IL-10 and TGFb1, and has been studied in the context of irritable bowel syndrome (4). 

Food intolerance symptoms are diverse and can manifest in various ways, including gastrointestinal, respiratory, skin, and even neurological symptoms such as migraines (5-8). These signs may appear hours or even days after consuming the triggering food, making diagnosis challenging. 

This condition can arise at any stage of life, even if the individual has consumed the food for years without symptoms. Due to its inflammatory nature and delayed reaction, early recognition of food triggers can contribute to proper symptom management and improved quality of life. 

What Is the Difference Between Food Intolerance and Food Allergy? 

According to a panel of experts from the National Institute of Allergy and Infectious Diseases (NIAID) in 2010, food allergy is defined as an adverse health reaction resulting from a specific and reproducible immune response to food exposure. 

In contrast, food intolerance refers to non-immunological reactions, which may be related to metabolic, toxic, pharmacological, or still poorly understood mechanisms (9). 

Food allergy involves an exaggerated immune system response, even to small amounts of the food, primarily mediated by immunoglobulin E (IgE) and classified as a type I hypersensitivity reaction. Food intolerance, which is more common, results from factors such as food contamination, pharmacological reactions, or metabolic and neuropsychological changes (10-11), and is mediated by immunoglobulin G (IgG). 

Food allergy affects about 6-8% of children under three years old and approximately 3% of adults (12). Its incidence is higher in individuals with other allergic conditions, occurring in 38% of children with atopic dermatitis and 5% of those with asthma (13). 

Despite this distinction, confusion between the two concepts is frequent, as both can be triggered by the same foods. However, unlike the immediate immune reactions of food allergy, intolerances may have a delayed onset and be influenced by factors such as stress, infections, and the use of antibiotics and anti-inflammatory drugs, which compromise intestinal permeability. 

Food allergies usually develop in childhood and have a low remission rate over time, whereas intolerances can arise at any stage of life. 

Accurate diagnosis of these conditions is essential to ensure proper clinical treatment, and increasingly specialized tests allow for a more precise distinction between them. 

Learn more about the differences between food allergies and food intolerance in our dedicated article on the topic. 

What Are the Main Symptoms of Food Intolerance? 

Food intolerance symptoms can vary widely among individuals, depending on the type of food involved and the degree of intolerance. Although the gastrointestinal tract is the most affected, symptoms in other systems can also occur, making diagnosis challenging. The most common symptoms include (6,7,14): 

• Diarrhea
• Constipation
• Stomach pain
• Bloating
• Acid reflux
• Gas
• Irritable bowel syndrome
• Muscle and joint pain
• Fatigue
• Headaches
• Skin infections

 Which Foods Most Commonly Cause Intolerance? 

The foods that most commonly cause intolerance vary depending on the type of substance the body has difficulty digesting or metabolizing. Among the most common are (15): 

• Dairy (milk, cheese, yogurt, butter): Lactose intolerance, which we have already discussed on the blog, is one of the most frequent types, due to the body’s inability to digest the sugar present in milk.
• Gluten (wheat, barley, rye, and their derivatives): Unlike celiac disease, gluten intolerance can cause gastrointestinal discomfort and fatigue without involving the immune system. Read more about gluten intolerance in this article.
• Fructose: Fructose intolerance is related to the difficulty in metabolizing the sugar found in fruits, vegetables, and some artificial sweeteners.
• Histamine: Commonly found in fermented foods such as aged cheeses, wines, processed meats, and some vegetables, histamine intolerance can trigger reactions like headaches and digestive disorders.
• Seafood and fish: Some individuals experience adverse reactions to fish and seafood due to naturally occurring compounds in these foods.
• Eggs: Egg intolerance may be linked to difficulties digesting proteins found in either the egg white or yolk.
• Nuts and seeds (almonds, walnuts, cashews, peanuts): Although often associated with allergies, some people may experience intolerance to these foods.
• Soy and its derivatives: Soy contains compounds that can be difficult to digest, leading to gastrointestinal symptoms.
• Legumes (beans, lentils, peas, chickpeas): These foods can cause abdominal discomfort and gas due to fiber fermentation in the intestines.
• Food additives (colorants, preservatives, and artificial sweeteners): Some individuals may be sensitive to additives such as monosodium glutamate (MSG), sulfites, and aspartame.

How Is Food Intolerance Diagnosed? 

Diagnosing food intolerance is challenging due to its non-specific symptoms, lack of immediate response, and limitations of conventional tests, such as skin tests. 

Various mechanisms may be involved, including enzyme deficiencies, changes in gut microbiota, and gastrointestinal dysfunctions, making precise identification more complex (9). 

Additionally, factors such as stress, infections, and prolonged use of antibiotics can compromise intestinal mucosa integrity, increasing susceptibility to food intolerance. 

The clinical evaluation begins with a detailed history, including diet and lifestyle. For patients with persistent gastrointestinal symptoms, laboratory tests, endoscopy, and stool analysis may be performed to rule out organic diseases. 

In the absence of identifiable pathologies, the diagnosis generally falls under functional gastrointestinal disorders, such as irritable bowel syndrome (IBS) or functional dyspepsia (16). 

Scientific advancements have facilitated the identification of food intolerances through innovative tests, such as the A200, which analyze reactions to various foods from a simple serum sample. These tests allow for better clinical management, providing significant benefits to patients’ quality of life. 

What Are the Treatment Options and Dietary Alternatives? 

Many individuals suffer from chronic food intolerance to specific foods. It is estimated that about 20% of the population may experience some type of adverse reaction to certain foods. 

Identifying and eliminating foods that cause hypersensitivity leads to significant improvements in many patients’ quality of life, offering benefits ranging from relief of gastrointestinal symptoms to reduced inflammation and skin problems. 

The initial therapeutic approach for food intolerance involves eliminating foods to which the individual has specific antibodies. The detection of elevated IgG antibodies against certain foods can be a useful tool in identifying substances that trigger adverse reactions. 

Excluding these foods from the diet often results in a noticeable improvement in symptoms, which may include acne, joint pain, digestive disorders, and chronic fatigue. In approximately 75% of cases, removing these foods leads to a substantial reduction or even disappearance of symptoms. 

After six months of food elimination, the identified foods can be gradually reintroduced, allowing for an assessment of the body’s tolerance. This process should be conducted under professional guidance to prevent symptom recurrence and ensure a balanced and nutritious diet. 

What Tests Does SYNLAB Offer for Food Intolerances? 

SYNLAB offers specialized tests for investigating different types of food intolerances, helping to identify sensitivities and intolerances. The key tests include: 

• A200 Test: Determines the presence of IgG antibodies in serum against 216 food proteins (vegetables and greens, legumes, dairy and eggs, fish and seafood, meats, fruits, nuts, herbs and spices, cereals, and grains, among others). With a simple blood sample, you can identify which foods may be potentially harmful to your health.
  This test is recommended for patients with gastrointestinal and musculoskeletal disorders, respiratory and dermatological conditions, neurological and psychological diseases, among others. You can learn more about the A200 test in the article “A200 Test: Everything You Need to Know.“ 

• Lactose Test: A genetic test for lactose intolerance, analyzing the patient’s DNA to detect the presence of variants in the MCM6 gene associated with adult-onset lactose intolerance.
  This test is recommended for assessing hypolactasia in adults with clinical symptoms of lactose intolerance, such as abdominal pain and bloating, gas, and diarrhea, as well as in cases of suspected lactose intolerance. 

• Celia Test: A test for gluten intolerance, consisting of a genetic study analyzing risk haplotypes HLA-DQ2 and HLA-DQ8. The test evaluates the alleles DQA1*0501 and DQB1*0201 of the HLA-DQ2 haplotype (associated with 90% of gluten intolerance cases) and DQA1*0301 and DQB1*0302 of the HLA-DQ8 haplotype.
  This test is recommended for individuals with clinical suspicion and negative serological studies before undergoing a duodenal biopsy, for investigating genetic susceptibility in relatives of celiac patients, for individuals with positive serological studies, and for those following a gluten-free diet without a confirmed diagnosis, requiring gluten reintroduction after an exclusion diet. 

• Intolerance 2: A test for both gluten and lactose intolerance. The Intolerance 2 test allows the identification of genetic predisposition to celiac disease through the analysis of HLA-DQ2 and HLA-DQ8 haplotypes, as well as primary lactose intolerance through the -13910C>T variant in the MCM6 gene, responsible for lactase enzyme production, associated with 90% of lactose intolerance cases.
  This test is recommended for patients with clinical suspicion of celiac disease and negative serological tests before duodenal biopsy, for patients with positive serology for celiac disease who refuse a duodenal biopsy, and for those with symptoms compatible with celiac disease and/or lactose intolerance. 

• Fructose Test: A test for fructose intolerance that evaluates three common variants in the ALDOB gene (A149P, A174D, N334K), responsible for 90% of cases. As an alternative to the breath test, this analysis is performed using a blood sample, avoiding direct exposure of the patient to substances.
  This test is recommended for children with clinical symptoms and nutritional or familial characteristics suggestive of fructose intolerance, as well as for cases of suspected fructose malabsorption.

Get to Know SYNLAB – A Leading Provider of Medical Diagnostic Services! 

Performing accurate and up-to-date tests is essential for precise diagnoses and the best treatment strategies. SYNLAB is here to help. 

We offer high-quality diagnostic solutions with strict quality control for companies, patients, and doctors. Present in Brazil for over 10 years, we operate in 36 countries across three continents and are the leading provider of diagnostic services in Europe. 

Contact the SYNLAB team and learn more about the available tests! 

References 

1. Bricks LF. Reações adversas aos alimentos na infância: Intolerância e Alergia alimentar – atualização. Pediatria (São Paulo). 1994;16(4):177-185.

2. Sten Dreborg. Debates in allergy medicine: food intolerance does not exist. Dreborg World Allergy Organization Journal (2015) 8:37. DOI 10.1186/s40413-015-0088-6

3. Beyer K, Teuber SS. Food allergy diagnostics: scientific and unproven procedures. Curr Opin Allergy Clin Immunol. 2005;5(3):261–6.

4. Sentsova TB, Vorozhko IV, Isakov VA, Morozov SV, Shakhovskaia AK.[Immune status estimation algorithm in irritable bowel syndrome patients with food intolerance]. Eksp Klin Gastroenterol. 2014;(7):13-7.

5. Collard J. Food Allergy and Intolerance. Pract Nurse. 2010;39(1):17–21.

6. Guo H, Jiang T, Wang J, Chang Y, Guo H, Zhang W. The Value of Eliminating Foods According to Food-Specific Immunoglobulin G Antibodies in Irritable Bowel Syndrome with Diarrhoea. J Int Med Res. 2012;40(1):204–

7. Kumar R, Kumar M, Singh M, Bisht I, Gaur S, Gupta N. Prevalence of food intolerance in bronchial asthma in India. Indian J Allergy Asthma Immunol. 2013;27(2):121.

8. Gaur S, Kumar R. Food allergy or food intolerance.? Indian J Allergy Asthma Immunol. 2013;27(2):93.

9. Boyce, J.A.; Assa’ad, A.; Burks, A.W.; Jones, S.M.; Sampson, H.A.; Wood, R.A.; Plaut, M.; Cooper, S.F.; Fenton, M.J.; Arshad, S.H.; et al. Guidelines for the diagnosis and management of food allergy in the united states: Summary of the NIAID-sponsored expert panel report. J. Allergy Clin. Immunol. 2010, 126, 1105–1118.

10. Ferguson A. Definitions and diagnosis of food intolerance and food allergy: consensus and controversy. J. Pediatr, 121:S7-11, 1992.

11. Burks AW, Sampson HÁ. Diagnostic approaches to the patient with suspected food allergies. J Pediatr. 121:S64-71, 1992.

12. https://ada.com/pt/conditions/food-allergy/

13. Alergia alimentar [Internet]. ASBAI. 2019 [cited 2024 May 6]. Available from: http://asbai.org.br/alergia-alimentar-4

14. Wilders-Truschnig M, Mangge H, Lieners C, Gruber H-J, Mayer C, März W. IgG antibodies against food antigens are correlated with inflammation and intima media thickness in obese juveniles. Exp Clin Endocrinol Diabetes Off J Ger Soc Endocrinol Ger Diabetes Assoc. 2008;116(4):241–5.

15. Zingone F, Bertin L, Maniero D, Palo M, et al. Myths and Facts about Food Intolerance: A Narrative Review. Nutrients. 2023 Nov 30;15(23):4969. doi: 10.3390/nu15234969.

16. Lomer MC. Review article: the aetiology, diagnosis, mechanisms and clinical evidence for food intolerance. Aliment Pharmacol Ther. 2015 Feb;41(3):262-75.