What is Food Intolerance?

Food intolerance occurs when individuals experience nonimmunological, meaning not related to or caused by an immune response, adverse reactions to a given food.¹ Although both conditions fall under the umbrella of food hypersensitivity,² food intolerance is a distinct entity from food allergy. Food allergy is an immunological adverse reaction that occurs when an individual is exposed to a given food.¹ Food intolerance elicits a dose-dependent response, meaning that the severity of the adverse reaction is related to the amount of the ingested food; in contrast, for individuals with food allergies, exposure to even a very small amount of the food allergen can trigger a severe reaction.³

There are various types of food intolerance, but they often share common symptoms that affect the gastrointestinal (GI) tract; these symptoms include abdominal pain, nausea, flatulence, bloating, and diarrhea.^2–4 Common types of food intolerance include:

Lactose intolerance: Lactose intolerance occurs when individuals with lactose malabsorption (inability to absorb lactose) experience symptoms such as abdominal pain, bloating, and diarrhea following the consumption of lactose-containing foods.^2,4 Lactose malabsorption is caused by a deficiency in lactase, the enzyme that digests lactose; lactase deficiency can occur gradually as individual ages, or it can be caused by abnormalities in the intestines as a result of conditions such as viral gastroenteritis, inflammatory bowel disease (IBD), chemotherapy, or malnutrition, among others.^2–4

Non-celiac gluten/wheat sensitivity (NCGWS): NCGWS occurs when individuals have a sensitivity to gluten or other components of wheat but lack celiac antibodies or allergic markers. Individuals with NCGWS might experience intestinal symptoms, such as bloating, abdominal pain, and diarrhea, and extraintestinal symptoms, such as fatigue, headache, and weight loss.^2,4 

Histamine intolerance: It is believed that histamine intolerance stems from increased levels of histamine in the blood due to consumption of histamine-rich foods and an inability to properly metabolize histamine.^2–4 It is suspected that a lack of diamine oxidase (DAO) activity contributes to histamine intolerance. In addition to GI symptoms, other symptoms include neurological symptoms (eg, headaches, dizziness) and cardiovascular symptoms (eg, lowered blood pressure, palpitations, tachycardia), as well as rarer respiratory (eg, rhinitis, difficulty breathing) and cutaneous (eg, itching, flushing) symptoms.^3,4

Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs): FODMAPs are short-chain carbohydrates that are poorly digested, which results in the production of short-chain fatty acids (SCFAs) and gas that can then cause symptoms such as abdominal pain, diarrhea, and flatulence, especially in susceptible individuals, such as those with irritable bowel syndrome (IBS). FODMAPs are found in fruits, vegetables, diary, cereals, and sweeteners, and examples include lactose, fructose, fructans, mannitol, and sorbitol.^2,4

Hereditary fructose intolerance (HFI): HFI is a rare autosomal disorder wherein individuals cannot metabolize fructose correctly, leading to symptoms such as nausea, abdominal pain, and diarrhea following consumption of foods high in fructose, including honey, fruits, and vegetables.^2,4

Non-HFI: Non-HFI stems from an impairment in fructose uptake in the small intestine.^2,4

Diagnosis varies based on the type of food intolerance. For example, lactose malabsorption can be diagnosed via enzymatic assays, genetic tests, and noninvasive breath tests,^2–4 and HFI can be diagnosed with the use of Benedict’s test and a glucose dipstick test,^2,4 whereas determining the presence of NCGWS or FODMAP intolerance largely relies on patient self-reports.⁴ When NCGS is suspected, the Salerno Experts’ Criteria⁵ can be utilized for diagnosis. Put simply, this process involves establishing baseline symptoms to a gluten-containing diet, adherence to a gluten-free diet to determine if symptoms improve, and, among those who experience symptom improvement with a gluten-free diet, a gluten challenge. While a hydrogen breath test exists for the diagnosis of non-HFI, results can be inconsistent and its clinical utility is thus debated.^2,4 Overall, there is a lack of validated tests for food intolerance, making diagnosis challenging.^3,4 Treatments differ based on the type of food intolerance and should be personalized to the individual; treatment commonly involves altering one’s diet to avoid or lower intake of foods that cause adverse reactions.^2–4

Bottom line

Food intolerance encompasses a variety of conditions that often cause symptoms such as abdominal pain, bloating, and diarrhea. Diagnosis can be challenging, and treatment often involves dietary changes. Consult with a doctor if you suspect you have food intolerance.

Sources

1. Boyce JA, Assa’ad A, Burks AW, 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(6):1105–1118. 
2. Hage G, Sacre Y, Haddad J, et al. Food hypersensitivity: distinguishing allergy from intolerance, main characteristics, and symptoms-a narrative review. Nutrients. 2025;17(8):1359. 
3. Gargano D, Appanna R, Santonicola A, et al. Food allergy and intolerance: a narrative review on nutritional concerns. Nutrients. 2021;13(5):1638. 
4. Zingone F, Bertin L, Maniero D, et al. Myths and facts about food intolerance: a narrative review. Nutrients. 2023;15(23):4969.
5. Catassi C, Elli L, Bonaz B, et al. Diagnosis of non-celiac gluten sensitivity (NCGS): the Salerno Experts’ Criteria. Nutrients. 2015;7(6):4966–4977.