When Can a Person Be Allergic to a Sugar? Alpha-Gal Syndrome Explained

Most food allergies are caused by proteins. Contrary to myth, sugars don’t typically cause allergic reactions—they’re more often linked to intolerances or sensitivities.

But there’s an exception: Alpha-Gal Syndrome (AGS). This emerging, often-misdiagnosed condition occurs when a tick bite makes people allergic to a sugar in mammal meat. A CDC study estimated that up to 450,000 people in the U.S. may be affected, and numbers are rising.

What Makes AGS Unique?

• Unlike most food allergies, AGS involves an immune response to a sugar (galactose-alpha-1,3-galactose), not a protein.
• This sugar is present in most mammalian meat but not in humans, birds, fish, or apes.
• Cause: Lone star tick bites transmit alpha-gal, triggering allergic antibodies that cause reactions upon later consumption of mammal meat (e.g., beef, pork, lamb).
• Exposure can also occur through gelatin or other mammal-based products.

Symptoms of Alpha-Gal Syndrome

• Abdominal pain, diarrhea, nausea
• Hives, swelling
• Anaphylaxis in severe cases
• Some patients only experience gastrointestinal symptoms
• Timing: Unlike typical food allergies (minutes), AGS reactions often appear 2–8 hours after eating

This delayed onset makes AGS an elusive diagnosis. Even when clinicians know of it, proper recognition and testing can be challenging.

Foods That Contain Alpha-Gal

• Mammalian meat: beef, pork, lamb, venison, rabbit
• Organs (higher concentrations)
• Gelatin (especially in medical products)
• Lard
• Meat broth, stock
• Certain medications or medical products (e.g., cetuximab)
• Milk contains alpha-gal, but many patients tolerate it

Foods That Do Not Contain Alpha-Gal

• Seafood
• Poultry
• Eggs

Diagnosing Alpha-Gal Syndrome

Diagnosis starts with a detailed history:

• Possible tick exposure or bites
• Timing of symptoms (2–8 hours after eating mammal products)

Testing:

• Blood test for alpha-gal IgE antibodies
• Important caveats: high false-positive rate, negative standard beef/pork tests, need for specialist interpretation
• Additional options: gelatin-specific IgE, basophil activation testing (available in select centers)
• Differential diagnosis: pork-cat syndrome and other food allergies

Treatment of AGS

• Strict avoidance of triggering foods and products
• Always carry injectable epinephrine
• Preventing tick bites is critical

Prevention tips:

• Stay on trails and avoid tall grass/bushes
• Wear long sleeves and pants; treat clothing with permethrin
• Use EPA-registered insect repellent
• Check yourself, your family, and pets for ticks after being outdoors
• Remove ticks promptly and clean the area thoroughly

Effects of Climate Change

As global warming expands tick populations, AGS is likely to become a more widespread health concern. Awareness of its unique presentation is vital for timely referral, diagnosis, and management.

References

• CDC: Alpha-Gal Syndrome
• Alpha-Gal Information: Diagnosis and Testing

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