Do Foods or Plants Contain IgG?
No, foods and plants do not naturally contain Immunoglobulin G (IgG) antibodies—IgG is an antibody produced exclusively by the mammalian immune system in response to antigens, not a component inherent to plant or animal food sources.
Understanding IgG in the Context of Food
IgG antibodies are immunoglobulins synthesized by B lymphocytes in mammals as part of the adaptive immune response. They circulate in blood and other body fluids but are not structural components of foods themselves 1.
The IgG-Food Relationship: Immune Response, Not Food Content
IgG antibodies develop against food antigens, not within foods: When individuals consume foods, their immune system may produce IgG antibodies in response to specific food proteins (antigens) such as casein, cow's milk, wheat, gliadin, egg whites, and rice 1.
IgG food reactivity reflects immune exposure: Elevated IgG antibodies to specific foods indicate prior immune system exposure to those food antigens, not that the foods contain IgG 2, 3.
IgG4 to foods is a marker of tolerance, not allergy: Food-specific IgG4 antibodies typically represent immune tolerance rather than pathological reactivity, and their presence does not indicate food allergy or intolerance in most clinical contexts 4.
The Exception: Contamination in Biological Products
IgG in Intravenous Immunoglobulin Preparations
The only scenario where IgG might be associated with "food products" involves pharmaceutical preparations derived from human blood:
Intravenous IgG preparations may contain trace IgE: Commercial intravenous immunoglobulin products used for replacement therapy can contain small amounts of IgE antibodies, including food-specific IgE to house dust mite, rye grass, and cow's milk, as well as IgG anti-IgE antibodies typically found in atopic patients 5.
This represents donor antibodies, not food-derived IgG: These immunoglobulins come from pooled human plasma donors, not from the foods themselves 5.
Clinical Implications: IgG Testing for Food Reactions
When IgG Food Testing May Have Limited Utility
- IgG4 testing lacks diagnostic value in adults: In adult patients with chronic urticaria and suspected food allergy, food-specific IgG4 testing showed no clinical utility—none of the IgG4-positive patients demonstrated adverse reactions to corresponding foods on double-blind placebo-controlled challenges 4.
Emerging Evidence in Specific Conditions
IgG-guided elimination may benefit IBS: In irritable bowel syndrome, dietary elimination based on elevated IgG antibodies to foods resulted in a 10% greater reduction in symptom scores compared with sham diet (26% improvement in compliant patients), though this remains an area requiring further validation 3.
Lipedema shows paradoxical IgG patterns: Women with lipedema exhibit more frequent IgG food reactivities despite significantly lower total IgG levels (1747.1 vs 2974.8 AU; p<0.001), suggesting mucosal immune dysregulation rather than food-derived IgG 6.
Common Pitfalls to Avoid
Do not confuse IgG to foods with IgG in foods: The distinction is critical—IgG antibodies are produced by the immune system in response to food antigens, not components naturally present in the foods themselves 1.
IgE-mediated food allergy is distinct from IgG reactivity: Food allergies involve IgE-mediated immunological responses to food antigens, while IgG responses typically represent exposure or tolerance 1.
Alpha-gal syndrome involves IgE to a carbohydrate epitope: This condition represents IgE-mediated allergy to galactose-alpha-1,3-galactose present in mammalian meat, not IgG in the meat itself 1, 7.