I learned about food sensitivities and delayed reactions the hard way. My gluten sensitivity shows up about 48 hours after I eat it. No fireworks on the day. Two days later: foggy head, mouth ulcers, upset stomach and not feeling myself. It took me years to make the connection. Sadly that delay and confusion is common, on average people with coeliac disease see 10-15 different specialists before stumbling on the correct diagnosis.
People mix up allergy, intolerance, and sensitivity. Each means something different. Each has its own physiology and common triggers. Below, I explain all three in plain english. Then you’ll get a short one-week test you can run, with a diary, to learn what matters for you. I hope this will help you avoid the same mistakes I made and identify then remove foods which trigger your symptoms.
The three categories of food reactions
1) Allergy
What it is
An allergy is your immune system reacting to a food protein. Allergic reactions are fast, often happening in minutes to an hour. They can be serious and in some cases life threatening.
What happens in the body
Your immune system makes IgE antibodies to a food trigger. These sit on histamine containing cells called mast cells. When you eat the food again, mast cells release histamine and other chemicals. That causes hives, swelling, wheeze, vomiting, or in severe cases, anaphylaxis. A tiny amount of the trigger can be enough to set off the reaction.
Common triggers
Peanuts, tree nuts, shellfish, fish, milk, egg, wheat, soy, sesame.
Important: If you suspect allergy, avoid the triggering food and speak to your GP or an allergist. Do not self-challenge.
2) Intolerance
What it is
An intolerance is not an immune problem. It is processing trouble. Your gut struggles because you are lacking a specific enzyme or can’t handle a chemical load. Symptoms are mostly digestive and linked to dose.
What happens in the body
This isn’t an immune reaction; it’s a problem with how your gut processes the food. The mechanism will vary depending on the triggering food, here are some common examples:
- Lactose needs to be broken down by the lactase enzyme. Low lactase results in gas, bloating, cramps, loose stools.
- FODMAPs (certain carbs in wheat, vegetables like onions, beans, and cauliflower, and some types of fruit) pull water and ferment in the colon producing gas and bloating. That stretches the gut and hurts.
- Histamine in aged and fermented foods needs the DAO enzyme to clear it. Low DAO or high intake → flushing, headache, congestion, gut upset.
Small amounts may be fine. Larger portions tip you over.
Common triggers
Lactose in milk and soft dairy. FODMAPs in wheat fructans, onions, garlic, legumes (peas and beans), apples, stone fruits, sugar alcohols. Histamine-rich foods such as aged cheese, cured meats, wine, tinned fish, and leftovers.
3) Sensitivity
What it is
A sensitivity is an immune reaction that is not IgE-mediated (often it is other types of antibodies like IgG, or IgA) and is usually delayed. It can take hours or days before you notice any changes. Symptoms can be gut-related or body-wide.
What happens in the body
Other immune pathways get involved (IgG/IgA, T-cells, inflammatory mediators). Think of it as a slow, smouldering response rather than a fast flare. Because it is delayed and sometimes threshold-based, patterns are hard to spot without a structured trial.
Common triggers
Gluten in people without coeliac disease (non-coeliac gluten sensitivity). Note that coeliac disease follows a similar pathway (IgA mediated) but is classed as an auto-immune disease rather than a sensitivity.
Dairy proteins (casein and whey) even when lactose is tolerated.
Other common triggers include eggs, soy, and sweetcorn (corn for our American friends!). Peanuts, tree nuts, and sesame cause sensitivity reactions for some, as do nightshades like tomatoes, peppers, and aubergine. Yeast, chocolate, and coffee are less common but affect some people.
Triggers vary person to person, and it can be tricky to connect the symptoms to the cause. Using a food/symptom diary or working with a functional medicine practitioner or nutritionist to go through an elimination / reintroduction diet can help you figure out what’s going on.
The sunday reset: a 7-day gluten-and-dairy reset
If you are having any of the common symptoms of sensitivity or intolerance type reactions such as bloating, ‘IBS-like’ gut problems, or signs of inflammation like joint pain or rashes which you can’t explain this simple test might help.
Aim: remove two high-impact suspects, keep everything else steady, and track symptoms. This is a safe, simple test for most adults.
Before you start:
- If you want coeliac testing, do that before removing gluten.
- If you have allergy red flags (hives, lip/tongue swelling, wheeze, throat tightness), speak to your doctor
What to remove for 7 days (or longer if you can)
All gluten (wheat, barley, rye, spelt, and foods made with them).
All dairy (milk, yoghurt, cheese, cream, butter).
Good swaps
- Carbs: sweet potatoes, rice, quinoa, gluten-free oats.
- Protein: eggs, poultry, fish, beans, lentils, tofu, tempeh.
- Fats: olive oil, avocado, coconut oil.
- “Dairy” stand-ins: unsweetened almond, soya, or oat milk; coconut yoghurt.
Keep the rest steady
Caffeine, alcohol, steps, bedtime. Fewer moving parts means a clearer signal.
Symptom diary (one minute a day)
Keep a journal, each evening, score 0–10 for: energy, mood, bloating, bowel habit, skin, pain, headache, sleep. Note any slips. See if your symptoms change. The changes may be subtle at first, if you think things may be improving then extend the trial up to 4-6 weeks. Sometimes sensitivity type reactions can take longer to settle.
Do this week
Remove gluten and dairy for 7 days. Keep a simple daily score. Nothing fancy.
What good looks like
Common wins: less bloating, steadier energy, clearer skin, fewer headaches, calmer joints, better sleep.
not seeing any benefit?
If nothing changes after removing dairy and gluten, that is useful too, especially if you try for the full 4-6 weeks. It suggests gluten and dairy are not your issue, and you can stop restricting. If you decide to reintroduce them into your diet follow these steps:
- Introduce one at a time: If you reintroduce both at the same time and you find your symptoms worsen or return you won’t be sure what is causing the issue.
- Run an experiment: When reintroducing each food back into your diet try to eat 2-3 portions on a single day. Avoid mixed dishes like lasagna or pizza which have both dairy and gluten.
- Look for changes: keep your symptom diary going, remember sensitivities can take 48-72 hours to show up, so wait for 2-3 days to see if there is any reaction.
- Repeat for the other food: If you successfully reintroduce the first food you chose with no problems you can repeat the steps above for the other.
Quick FAQ
How long should I eliminate?
Seven days will often give a signal. Four to Six weeks will be definitive if you have the time (and patience!).
Do I need a food sensitivity blood test?
Usually no. Most IgG panels are not reliable for diagnosis. Most FM practitioners will recommend using elimination and re-challenge, similar to the exercise described above. However there are some exceptions, like coeliac disease, if you are unsure speak to your doctor.
What about calcium if I cut dairy?
Leafy greens, almonds, tahini, tinned fish with bones, and fortified plant milks cover it. You can also use supplements if needed or you have other medical problems with risk factors for bone problems like osteoporosis (brittle bones), speak to your doctor if you have any concerns.
Can sensitivities improve over time?
Yes some people get to a place where they have healed their gut and can then tolerate things they struggled with before. Reduce triggers, support the gut, then re-test later ideally working with a nutritionist or FM practitioner.
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Disclaimer: Education only, not medical advice. Speak to your clinician before making significant changes, especially if you take medication, are pregnant, have complex conditions, or suspect allergy.
