In the age of Google, patients often present in clinical settings with some medical understanding or hunches about what may be driving their symptoms. Among them may be ideas around what foods their body cannot tolerate. It is important for the practitioner to then distinguish if their symptoms are related to immune reactions or something else. Continue reading to find out how to identify these differences for your patients.
Immunologic reactions to foods:
- Immunologic reactions create an inflammatory cascade to protect the body. The body produces specific antibodies to antigens, which are mainly proteins (and less often oligosaccharides or lipids). Trace amounts of the food allergen can trigger a reaction.
- These generally fall into 2 categories: immediate or delayed onset reaction.
- Immediate reactions are mediated by IgE antibodies. The reaction mostly occurs seconds or up to 30 minutes after exposure to a food allergen and lasts only for 1 day. Severe anaphylaxis occurs with mass rapid liberation of histamine from degranulated mast cells.
- For example, after eating prawns a patient experiences an episode of vomiting and tachycardia. This does not occur the following day when prawns are not eaten.
- Delayed reactions are mediated by IgG antibodies. The reaction occurs anywhere from 3 hours to 3 days following ingestion.
- For example, 1 day after eating a breakfast of toast and poached eggs, a patient experiences reflux and struggles to have a bowel movement for the next 2 days.
- Removing IgG trigger foods may lead to significant symptom reduction only after a couple of weeks.
- Both IgG and IgE reactions can be determined via blood testing.
- There are cross linkages between these two immunologic reactions. For example Mammalian Meat Allergy, an IgE response to “alpha-gal” oligosaccharide present in mamalian meat can produce delayed anaphylaxis after red meat consumption. Linked with a tick bite, these patients often accumulate IgG antibodies toward beef, deer, goat, pork, rabbit and lamb.
Non-immunologic reactions to foods:
- Non-immunological reactions do not trigger inflammation.
- They can be broadly classed into enzymatic or malabsorption reactions.
- Lactose intolerance (deficiency in the lactase enzyme) will manifest diarrhoea 30 minutes to 2 hours following ingestion of at least 12g of lactose (tall glass of cows milk). Trace amounts of lactose, eg in medications or supplements will most likely be tolerated since this is not an immunologic reaction.
- Histamine intolerance (deficiency in Diamine Oxidase enzyme) may manifest as a rash and headache 30 minutes to 4 hours after ingestion of a glass of red wine and dark chocolate. The patient may experience nausea which can be traced to consumption of high histamine foods and resolves immediately when these foods are avoided.
- Fructose malabsorption (reduced capacity for uptake of fructose into small intestinal cells) can lead to abdominal fullness and weight loss lasting up to 2 days.
- FODMAP intolerance often signals an imbalanced gut microbiota leading to gas and bloating after consumption of long chan fibres (eg garlic and onion). However, long term avoidance of FODMAP foods can negatively impact the gut microbial balance further. Avoiding IgG trigger foods has shown greater efficacy for managing IBS.