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What is Food Intolerance ?

What is Food Intolerance ?


Food intolerance is essentially an abnormal reaction to certain foods which can manifest itself in a number of ways. It may be the result of various different mechanisms, however Cambridge Nutritional Sciences (CNS) is primarily interested in those food intolerances in which an immune response occurs (i.e. IgG antibodies are produced), and has developed tests that detect the presence of these antibodies using a pin-prick sample of blood. Other mechanisms of food intolerance are not mediated by the immune system. Typical examples include:

  • Enzyme insufficiency/ deficiency
    • Lactase as in lactose intolerance (bloating, diarrhoea, abdominal pain)
  • Chemical / pharmacological sensitivity
    • MSG in Chinese food ( headaches, sweating, dizziness)
    • Sulphites in dried fruits and vegetables, wine, beer (asthma)
    • Vasoactive amines such as phenylethylamine in chocolate, red wine (migraines)

Is There A Difference Between Food Allergy And Food Intolerance?

Many people think that food allergies and food intolerances are the same, however there are many significant differences:

  • Allergies tend to produce an immediate response after ingestion whereas an intolerance can produce delayed symptoms up to 3 days after ingestion.
  • Allergies are IgE mediated whereas intolerances produce IgG antibodies.
  • The incidence for allergies is relatively low, whereas the incidence for intolerances is relatively high.
  • Allergies tend to be a result from infrequent exposure whereas intolerances result from frequent exposure.
  • The mechanism for an allergic response involves a rapid release of histamine from mast cells, whereas the mechanism for food intolerance involves the slow formation of antigen/antibody complexes which are deposited in tissues and cause inflammation.
  • Allergies tend to produce classical predictable symptoms such as rashes, sneezing, hay fever, breathing difficulties, asthma, and even anaphylactic shock, however intolerances can produce many symptoms that can affect any part of the body and patients often report multiple symptoms.
  • Allergies can be fatal whereas food intolerances are not life-threatening.
  • Allergies can last a lifetime, however food intolerances can be reversed by the elimination of foods that produce high IgG levels.
  • Allergies show positive in a skin-prick test, whereas food intolerances give a negative result.
  • Allergies are often self-diagnosed as it is usually obvious which food or foods cause the problem, but it is much harder to say which foods are causing the problem with food intolerances and therefore the importance of IgG tests.

Mechanism Of Food Allergy

The mechanism of classical food allergy involves the release of inflammatory mediators after IgE antibodies bind to a mast cell. The sequence of events is as follows:

  • Food antigen stimulates a class of lymphocytes called Th2 helper T cells.
  • These Th2 helper T cells secrete cytokines that instruct B lymphocytes to produce antigen specific IgE antibodies.
  • IgE antibodies bind to mast cells and stimulate the release of inflammatory mediators, including histamine.
  • Inflammation is caused, producing classical allergic symptoms such as sneezing, watery eyes, itching, rashes, difficulty breathing etc.

Mechanism Of Food Intolerance

The mechanism of food intolerance involves the production of antigen/antibody complexes which are deposited in the tissues, triggering the release of inflammatory chemicals causing damage and inflammation in that particular tissue. This could be in any part of the body such as for example, the gut, causing IBS symptoms; in the joints, producing symptoms of arthritis; in the head producing migraines etc. The sequence of events is as follows:

  • Partially digested foods pass between gut cells into the blood.
  • These proteins are recognised as ‘foreign’ and food specific IgG are produced in response.
  • Antigen/ antibody complexes form between the partially digested foods and the IgG antibodies. The symptoms of food intolerance tend to be delayed because this formation of complexes is a gradual process – it does not happen immediately.
  • The complexes are deposited in tissues (could be anywhere in body such as gut, head, skin etc.).
  • Complement is activated which causes respiratory burst in neutrophils, release of proteolytic enzymes, mast cell mediators and vasoactive peptides, and aggregation of platelets.
  • Complement and macrophages stimulate inflammation, although complement helps to prevent smaller complexes going on to form larger complexes.
  • C2 and C5 (part of the enzyme cascade) can release histamine too.
  • Macrophages release inflammatory mediators such as interleukin-1, tumour necrosis factor, reactive oxygen species and nitric oxide (NB: The complement system is an enzyme cascade that helps defend against infection).

Symptoms Of Food Intolerance

There are many symptoms associated with food intolerances and as they tend to be delayed it can be difficult to determine which food is causing the problem, and therefore tests for IgG antibodies can be extremely valuable. Symptoms include:

  • Arthritis, fibromyalgia, joint pain
  • Asthma
  • Anxiety, depression
  • Attention deficit or hyperactivity disorders
  • Bed wetting and chronic bladder infections
  • Dark circles or puffiness under the eyes
  • Headaches or migraine
  • Insomnia, lethargy, “fogginess”
  • Myalgic Encephalomyelitis / Chronic Fatigue Syndrome
  • Persistent cough, catarrh
  • Sinusitis
  • Skin disorders including eczema, rashes and spots
  • Weight retention problems
  • Chronic respiratory symptoms (wheezing/ bronchitis)
  • Auto-immune disorders
  • Fatigue
  • Palpitations
  • Water retention
  • Bowel problems (colitis, IBS, constipation, diarrhoea, bloating, abdominal pain, flatulence)

Foods Commonly Associated With Food Intolerance

The most common foods that are associated with food intolerances are:

  • Cow’s milk
  • Eggs
  • Nuts
  • Wheat
  • Gluten
  • Soya
  • Yeast

The Link Between IgG Antibodies And Symptoms

It is important to note that IgG antibodies are produced all the time in normal individuals, but these do not usually cause symptoms provided that:

  • The Immune system is functioning efficiently and /or
  • The permeability of the gut is not increased.

Symptoms tend to occur when the immune system is compromised and/ or the permeability of the gut is increased

These mechanisms will be described below and compared with the normal response to food in healthy individuals, i.e. the normal response to food where both the gut wall and immune system are healthy.

Responses To Foods

1. Normal

In any normal individual, some partially digested foods pass between the gut cells into the blood stream and trigger an immune response. The sequence of events is as follows:

  • Healthy gastro-intestinal tract and healthy immune system.
  • Foods are digested to basic components (glucose, amino acids and fatty acids) and absorbed through the gut lining into blood stream.
  • Some partially digested foods will pass between gut cells directly into blood stream.
  • Antibodies (IgG) produced against these partially digested foods and form antigen/ antibody complexes.
  • An efficient immune system (i.e. macrophages) will clear all these complexes.
  • No complexes left to be deposited in tissues.
  • Therefore, no damage or inflammation of tissues.
  • Therefore, no symptoms (despite an immune reaction occurring).
  • Therefore, antibodies are produced against food as a normal response to food, but it is not a problem due to the efficiency of the immune system.

2. Compromised Immune System

When the immune system is compromised, the sequence of events is similar to that of a normal response but there will be insufficient macrophages to clear away the complexes, and therefore these will be deposited in the tissues, producing an inflammatory response and therefore symptoms:

  • Healthy Gastro-intestinal tract but compromised Immune system.
  • Foods digested to basic components (glucose, amino acids and fatty acids) and absorbed through the gut lining into blood stream.
  • Some partially digested foods will pass between gut cells directly into blood stream.
  • Antibodies (IgG) produced against these partially digested foods and form antigen/ antibody complexes.
  • Insufficient macrophages to clear all the complexes.
  • Therefore excess complexes will circulate in the blood stream and be deposited in tissues (anywhere in body).
  • Damage and inflammation to the tissues occurs.
  • Therefore, symptoms produced.

3. Increased Gut Permeabilitya

In this situation, the immune system is working efficiently, but the gut wall becomes more permeable (i.e. there is an increase in the number of partially digested foods entering the blood stream), and the immune system becomes overloaded. Therefore not all of the immune complexes can be cleared away and therefore, excess complexes are deposited in tissues causing symptoms:

  • Normal healthy immune system, but increased gut wall permeability.
  • Increase in partially digested foods passing between gut cells directly into blood stream.
  • Antibodies produced against these partially digested foods with the formation of antigen/ antibody complexes.
  • Immune system becomes overwhelmed/ overloaded.
  • Insufficient macrophages to clear all the complexes.
  • Therefore excess complexes circulate in the blood and become deposited in tissues (i.e. anywhere in body).
  • Tissue damage and inflammation occurs.
  • Therefore, symptoms are produced.

Factors That May Exacerbate A Leaky Gut

The following factors can all put stress on a person’s health and can lead to increased gut permeability

  • Low levels of secretory IgA
    • Secretory IgA is an immune marker and is the first line of defence in the gut against bacteria, food residue, fungus, parasites and viruses.
  • Stress
    • Stress can deplete the body of secretory IgA and hence reduce the body’s defence system against foreign bodies. Also stress depletes the gut of good bacteria, and therefore allows an overgrowth of bad bacteria and yeast such as Candida.
  • Imbalanced gut flora
  • Mucosal injury due to infection or certain medical drugs
    • Non-steroidal Anti-Inflammatory Drugs (NSAIDS) e.g. Aspirin, damage the intestinal wall causing inflammation resulting eventually with an increase in permeability.
  • Parasites
    • Parasites also damage the intestinal wall causing inflammation, eventually resulting in an increase in permeability.
  • Lack of variation in the diet egg too much gluten
  • Low stomach acid
  • Low pancreatic enzymes
    • When the intestinal lining is damaged, the microvilli are also damaged thus reducing absorption of nutrients vital for the manufacture of digestive enzymes. Consequently foods are not fully digested, pass into blood stream and stimulate antibody response.
  • Poor nutrient status
    • Damage to the intestinal lining reduces nutrient absorption with the consequence of impaired gut repair, and therefore further impaired digestion and absorption.