Food Intolerance

How Food Intolerance Differs From Allergy

Food intolerance is a digestive system response that occurs when the body is unable to properly digest certain foods or food components. Unlike food allergies, which involve the immune system, food intolerances are generally less severe and primarily affect the digestive system. They can, however, lead to significant discomfort.

Common Types of Food Intolerance

1. Lactose Intolerance

Caused by: The body's inability to produce enough lactase, the enzyme needed to digest lactose (the sugar found in milk and dairy products).
Symptoms: Bloating, diarrhea, gas, and stomach pain after consuming dairy.

2. Gluten Intolerance (Non-Celiac Gluten Sensitivity)

Caused by: A reaction to gluten, a protein found in wheat, barley, and rye.
Symptoms: Bloating, stomach pain, fatigue, and headaches.
Note: Different from celiac disease, which is an autoimmune disorder.
Gluten or other wheat sugars: In a 2013 double-blind crossover trial, 37 people who believed they had non-celiac gluten sensitivity (and also had irritable bowel syndrome) first ate a diet low in fermentable short-chain sugars (FODMAPs) for 2 weeks, which improved their gut symptoms. When gluten (16 g a day) or a whey-protein placebo was then added without their knowing which, symptoms worsened to a similar degree with both; gluten-specific effects were seen in only 8% of participants, and the authors found no evidence of a specific or dose-dependent effect of gluten in these people.

3. Fructose Malabsorption

Caused by: Difficulty absorbing fructose, a sugar found in fruits, some vegetables, and honey.
Symptoms: Bloating, gas, diarrhea, and abdominal pain.
Not the same as hereditary fructose intolerance: Hereditary fructose intolerance is a rare inherited disorder (a defect in the liver enzyme aldolase B, passed on when both parents carry the gene). In it, eating fructose, sorbitol or table sugar (sucrose) causes abdominal pain, vomiting and metabolic upsets, including low blood sugar, that may prove fatal. When these sugars are removed from the diet the response is rapid and people can live a normal life span; survivors often develop a strong dislike of fruit, nuts and sweet foods (Cox 1994).

4. Histamine Intolerance

Caused by: The inability to break down histamine in foods due to low levels of diamine oxidase (DAO), the enzyme that metabolizes histamine.
Symptoms: Headaches, hives, flushing, and digestive issues.

Common Symptoms of Food Intolerance

Bloating and gas
Diarrhea
Stomach pain and cramps
Nausea
Headaches
Heartburn
Fatigue
Skin rashes

Causes and Risk Factors

Enzyme deficiencies: Lack of specific enzymes needed to break down certain foods (e.g., lactase for lactose intolerance).
Food additives: Reactions to artificial colors, flavors, or preservatives (e.g., sulfites and MSG).
Sensitivity to natural food chemicals: Such as caffeine or histamine.
Underlying conditions: Such as irritable bowel syndrome (IBS), which can exacerbate food intolerance symptoms.
Genetic predisposition: A family history of food intolerance may increase risk.

Diagnosis

Medical history and symptom assessment: The history of which foods were eaten, how much, and how soon symptoms followed points to possible triggers.
Elimination diet: Suspected foods are removed from the diet for a time and then added back one by one to identify the source of symptoms.
Breath tests: To diagnose lactose intolerance or fructose malabsorption.
Food diary: A record of meals and symptoms helps identify potential food intolerances.

Treatment and Management Strategies

Dietary adjustments:
- Leaving out trigger foods: People usually identify and leave out the foods that cause their symptoms.
- Alternatives: Lactose-free dairy products and gluten-free grains are common substitutes.
- Yogurt: A 2014 review explains that the lactose in yogurt is digested better than lactose in other dairy foods, because yogurt's live bacteria carry their own lactase enzyme. This enzyme survives stomach acid inside the bacteria and becomes active in the small intestine, digesting the lactose well enough to prevent symptoms in people with lactose intolerance. Plain (unflavored) yogurts showed somewhat more lactase activity than flavored ones, though flavored yogurts were still well tolerated (Savaiano 2014).
Enzyme supplements:
- Lactase supplements: For those with lactose intolerance.
Portion control: Eating smaller amounts of trigger foods may help reduce symptoms.
Hydration and a balanced diet: Enough fluids and a varied diet help keep nutrition adequate when some foods are left out.

Prevention Tips

Food labels: Ingredient lists show additives and allergens. US federal law names nine major food allergens (milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans and sesame); since January 1, 2023, sesame must also be declared as an allergen on packaged foods (US Food and Drug Administration).
Meal planning: Meals prepared at home without known triggers give the most control over ingredients.
A balanced diet: When whole food groups are left out, replacing their nutrients from other foods prevents deficiencies (see Complications below).

Complications of Food Intolerance

Digestive discomfort: Chronic symptoms can impact quality of life.
Nutritional deficiencies: Avoiding certain foods without proper substitutions can lead to deficiencies.
Social and emotional impact: Anxiety or stress related to food choices and dining out.

Key Research Papers

Cooper BT, Holmes GK, Ferguson R, Thompson RA, Allan RN, Cooke WT. Gluten-sensitive diarrhea without evidence of celiac disease. Gastroenterology. 1980;79(5 Pt 1):801-806. — PubMed PMID: 7419003
Maintz L, Novak N. Histamine and histamine intolerance. American Journal of Clinical Nutrition. 2007;85(5):1185-1196. — doi:10.1093/ajcn/85.5.1185
Catassi C, et al. Non-celiac gluten sensitivity: the new frontier of gluten related disorders. Nutrients. 2013;5(10):3839-3853. — doi:10.3390/nu5103839
Swagerty DL, Walling AD, Klein RM. Lactose intolerance. American Family Physician. 2002;65(9):1845-1850. PubMed PMID: 12018807
Gibson PR, Shepherd SJ. Evidence-based dietary management of functional gastrointestinal symptoms: the FODMAP approach. Journal of Gastroenterology and Hepatology. 2010;25(2):252-258. — PubMed PMID: 20136989
Halmos EP, et al. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology. 2014;146(1):67-75. — doi:10.1053/j.gastro.2013.09.046
Biesiekierski JR, et al. No effects of gluten in patients with self-reported non-celiac gluten sensitivity after dietary reduction of fermentable, poorly absorbed, short-chain carbohydrates. Gastroenterology. 2013;145(2):320-328. — doi:10.1053/j.gastro.2013.04.051
Boyce JA, et al. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel. Journal of Allergy and Clinical Immunology. 2010;126(6):S1-S58. — doi:10.1016/j.jaci.2010.10.007
Turnbull JL, Adams HN, Gorard DA. Review article: the diagnosis and management of food allergy and food intolerances. Alimentary Pharmacology & Therapeutics. 2015;41(1):3-25. — doi:10.1111/apt.12984
Lomer MCE. Review article: the aetiology, diagnosis, mechanisms and clinical evidence for food intolerance. Alimentary Pharmacology & Therapeutics. 2015;41(3):262-275. — doi:10.1111/apt.13041
Elli L, et al. Diagnosis of gluten related disorders: celiac disease, wheat allergy and non-celiac gluten sensitivity. World Journal of Gastroenterology. 2015;21(23):7110-7119. — doi:10.3748/wjg.v21.i23.7110
Cox TM. Aldolase B and fructose intolerance. FASEB Journal. 1994;8(1):62-71. — PubMed PMID: 8299892
Savaiano DA. Lactose digestion from yogurt: mechanism and relevance. American Journal of Clinical Nutrition. 2014;99(5 Suppl):1251S-1255S. — PubMed PMID: 24695892
US Food and Drug Administration. The FASTER Act: Sesame Is the Ninth Major Food Allergen. — fda.gov

Historical Background

The concept of food intolerance was distinguished from food allergy in the mid-20th century. Lactose intolerance was first scientifically described by Abraham Jacobi in the 1900s, while the enzyme lactase and its deficiency were characterized by Auricchio and Dahlqvist in the 1960s. The concept of non-celiac gluten sensitivity was first proposed by Cooper and colleagues in 1980, and histamine intolerance was formally described by Maintz and Novak in 2007.

PubMed Topic Searches

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