Food Allergies and Intolerances: What You Need to Know

what to know about allergies vs intolerances

These days it’s not very uncommon to hear someone commenting on the fact that they have an allergy towards a certain food. Very often in essence it’s actually a food intolerance. Either way, as the prevalence of both food allergies and intolerances continues to increase, it is important to fully understand what is what and to know what you can do.


Food allergies and intolerances are often confused, as their symptoms can seem similar. In fact, the two are quite different and it’s important to get familiarised with the two:

  • A food allergy involves the immune system, and happens when the body reacts to a protein in specific foods, which are usually harmless. Reactions are usually immediate and can occur after being exposed to very small amounts of the food. Symptoms of an allergic reaction manifest in many ways such as rashes, itching, hives, swelling and when severe, can lead to serious trouble breathing and death. The most common food allergies include eggs, peanuts, soy, milk, wheat, fish and shellfish. Food allergies affect around one in 20 children, and two in 100 adults. Up to 10% of babies may suffer from food allergies, but most of these will grow out of the allergy early in life.
  • A food intolerance, on the other hand, does not involve the immune system however is a chemical reaction that is triggered from substances that naturally occur in foods ( such as lactose or gluten) or that arise in food processing methods (such as preservatives, artificial colours and flavourings). Reactions are dose dependent and different people will tolerate different amounts of any given chemical. The most common intolerances include lactose, histamine, tartrazine (artificial food colour),sulphites (preservative), monosodium glutamate (MSG) and increasingly gluten. An intolerance to food is rarely life threatening and tends to occur hours or days after the food is eaten. Symptoms are generally described as an unpleasant reaction to a particular food involving tummy cramps, flatulence, vomiting and diarrhoea.

food allergy and intolerance guide


Herein lies another big difference between food allergy and food intolerance. There is a valid and reliable way to test and diagnose food allergies, however there isn’t for food intolerances (sorry folks!).

To diagnose food allergies currently, medics use skin tests, patch tests and blood tests to begin diagnosing a food allergy. However, none of these methods stand alone for a diagnosis. The results from these tests must be taken into consideration with the patient’s medical history and must be confirmed by an oral challenge which is the gold standard in diagnosing a food allergy. In the oral challenge, the suspected food is removed for a period of time with an elimination diet ( in conjunction with a dietitian) then reintroduced. The reintroduction process varies based on the severity of the suspected allergic reaction, how many foods are suspected to cause an allergic response and the results from previous allergy tests. Due to the risk associated, an oral food challenge should not be attempted independently, but either under medical supervision or with medical approval.

Unfortunately with intolerances ( apart from lactose) there are no blood, breath, stool tests that can accurately determine food intolerances. As tempting and promising as these tests claim to be and as much as you just want answers for now the science says it’s best to save your money! Personalised nutrition is where the nutrition world is moving, however we are not there just yet. If you suspect you have an intolerance, I would recommend getting in touch with a dietitian or registered dietitian to work out a bespoke plan for you. While you wait for an appointment, keep a very specific food diary of what food you eat when and what symptoms you feed after you eat certain foods.

what to know about food allergies


It is not known exactly how many people in the UK have a food allergy or an intolerance however we do know that the numbers are on the increase. In the UK, it is estimated that allergies affect 1 in 25 of the population, although 20 – 30% of people perceive themselves to have an intolerance or an allergy to one or more foods. There is no single explanation for why we are becoming more allergic to food however science has some theories which include:

  • Vitamin D deficiency:

    Most populations around the world are spending less time in the sun or using sunscreen which affects how much vitamin D we make and have in store in our bodies. Reduced production and increased body fat levels ( fat traps vitamin D making it unavailable for use) mean that the majority of people are vitamin D deficient. Vitamin D is vital in helping us develop a healthy immune system hence a deficiency makes us less susceptible to allergies.
  • Hygiene hypothesis:

    Many studies have shown that in countries where there is more exposure to dirt and parasites there are a significantly lower risk of allergies. Parasitic infections in particular are normally fought by the same mechanism involved in tackling allergies. With fewer parasites to fight, the immune system turns against things that should be harmless like food. It seems that early training of the immune to deal with pathogens is key to immune development.
  • Dual allergen exposure:

    This newer theory suggests that food allergy development is down to a balance between the timing, dose and form of exposure. For example it is thought that eating potential allergens during weaning can lead to a healthy response and protect the allergy developing as it leads to tolerance.
  • Too many antibiotics and pesticides:

    A healthy and diverse gut microbiota is key to developing a strong immune system as this decreases the likelihood of intestinal permeability which makes us more prone to allergies. It is believed the increased exposure to antibiotics and pesticides within the western world and well as diets low in fibre are taking our intestinal flora out of balance.
  • Changed farming practices:

    Compared to 100 years ago our farming practices have changed and as a result the quality of the food we are eating has also been affected. Our food is mass-produced and grown in the quickest way possible which means there are more potential immunologically active proteins in our food system hence increasing the potential for allergic reactions. This is the same with environmental toxins.
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  3. Seth D et al. 2020. Food Allergy: A review. Pediatr Ann. 1:49 (1)
  4. Turnbull J. 2015. Review article the diagnosis and management of food allergy and food intolerance. Aliment Pharmacol Ther.41(1):3-25
  5. Guandalini S:2011. Differentiating food allergies from food intolerances. 426-34.