Food Allergy, Intolerance or Sensitivity? What’s the Difference — and Why It Matters for Gut Health

By Lucy Sugars, Nutritional Therapist

If you’ve ever felt bloated, gassy, or foggy after eating — or noticed a skin flare-up, headache or fatigue that doesn’t make sense — you may have wondered if food could be to blame.

But with terms like allergy, intolerance, and sensitivity often used interchangeably, it’s no wonder people feel confused. As a nutritional therapist specialising in gut health, I regularly help clients untangle these reactions — and understand how to support their body.

Let’s break it down simply.

🚨 What is a Food Allergy?

A food allergy is a fast-acting, immune-mediated reaction — typically involving IgE antibodies. These reactions usually happen within seconds to minutes of eating the food and can be severe or even life-threatening (as in the case of anaphylaxis).

Common allergens include:

  • Peanuts and tree nuts
  • Shellfish
  • Milk and eggs
  • Wheat and soya
  • Oranges and fish

🧬 Important to know:

Food allergies are usually lifelong, as IgE antibodies have a long memory.

Reactions may worsen over time with repeated exposure.

They often run in families and are usually diagnosed via blood (IgE) or skin testing.

Allergies require clinical diagnosis and management, often with the use of an EpiPen.

⚠️ If you suspect a food allergy, speak to your GP for a referral to an NHS allergy clinic. As a nutritional therapist, I can support you once a diagnosis has been made — helping you find safe, nourishing alternatives. We cannot diagnose and cannot access food allergy testing, I cannot stress enough that this must be done via an NHS allergy clinic.

🍞 What is a Food Intolerance?

Food intolerance is not an immune reaction — it usually happens because the body struggles to digest certain substances. This can be due to:

  • A lack of digestive enzymes
  • Sensitivity to naturally occurring compounds in food
  • Overfermentation by gut bacteria

💨 Symptoms are mostly digestive and may include:

  • Bloating and abdominal pain
  • Diarrhoea or constipation
  • Excess gas

🔍 Common examples:

  • Lactose intolerance (lack of the enzyme lactase)
  • FODMAP sensitivity (fermentable carbs that irritate the gut)
  • Difficulty digesting legumes, gluten, or certain fibres

Intolerances can be frustrating — but they’re not life-threatening. With the right gut support (including enzyme or microbiome support), many people are able to reintroduce foods over time. This is an area I work with all the time and it can be life changing when you discover what foods your body is reacting to, so you can find nutritious alternatives to them instead.

🛡️ What is a Food Sensitivity?

Food sensitivities are delayed immune responses, often involving IgG or IgA antibodies rather than IgE. Unlike allergies, symptoms may appear hours to days after eating — making them tricky to pinpoint.

🔁 Common symptoms include:

  • Digestive issues (bloating, cramps, diarrhoea)
  • Headaches or migraines
  • Skin rashes or itching
  • Brain fog and fatigue
  • Difficulty losing weight
  • Respiratory issues (wheezing, sinus congestion)

🧠 These reactions are often linked to increased gut permeability, where food particles trigger immune responses due to a compromised gut lining.

💡 Good news:

Sensitivities are often reversible.

With gut repair and temporary removal of triggers, foods may be reintroduced.

A guided elimination and reintroduction protocol is the most reliable method — best done with professional support.

🧪 What About Testing?

While there are IgG-based sensitivity tests available, the science is mixed. They can sometimes help identify patterns, but results should be interpreted cautiously.

For many clients, I recommend:

  • Keeping a structured food and symptom diary
  • Running a short trial elimination (typically 3–4 weeks)
  • Following a gradual reintroduction protocol to assess tolerance

This avoids unnecessarily restricting the diet — which can impact gut and nutrient health if not done carefully.

🧬 Why This Matters for Gut Health

Your gut is home to 70% of your immune system. When it’s constantly triggered by reactive foods — whether through inflammation, fermentation, or immune responses — symptoms can build and healing becomes harder.

Identifying and managing food reactions can:

  • Calm inflammation
  • Reduce bloating and diarrhoea
  • Support skin and hormone health
  • Improve energy, mood, and focus
  • Help rebuild a stronger gut lining and more resilient microbiome

✅ Final Thoughts

If you’re dealing with ongoing digestive issues, skin flare-ups, or unexplained fatigue — food reactions may be part of the puzzle. The good news? With the right support, your gut can become more resilient, and many foods may be enjoyed again over time.

👉 Fill out my client intake form if you’d like to explore what might be going on with your gut and work together to uncover your triggers in a supportive, realistic way.