Food intolerance

# Overview
Food intolerance or food sensitivity is a negative reaction to a food that may or may not be related to the immune system or to food poisoning. It can be caused by the absence of specific chemicals or enzymes needed to digest a food substance, or by the body's responses and reactions to certain food constituents (chemicals) both natural or artificial.  Symptoms of food intolerance vary greatly, and can be mistaken for the symptoms of an allergy. While true allergies are associated with fast-acting immunoglobulin IgE responses, it can be difficult to determine the offending food causing an intolerance because if the immune system is involved, the response is likely to be IgG mediated and takes place over a prolonged period of time. Thus the causative agent and the response are separated in time, and may not be obviously related.  A deficiency in digestive enzymes can also cause some types of food intolerances. Lactose intolerance is a result of the body not producing enough lactase used to break down the lactose in milk. Gluten intolerance results in damage to villi in the small intestine, which makes it difficult for the body to absorb water and nutrients from foods. Another type of food intolerance is an intolerance to food chemicals such as salicylates or salicylate sensitivity. Salicylates are chemicals that can occur naturally in many foods. Salicylate sensitivity causes many symptoms the most common of which are: hives, stomach pain, headaches, mouth ulcers, and it has even been linked to ADD and ADHD.  Food intolerance can exist as a separate condition or contribute to the symptoms of complex syndromes such as Chronic Fatigue Syndrome CFS/CFIDS, Myalgic Encephalomyelitis  ME, Post-Viral Fatigue Syndrome PVFS and may involve causes such as Leaky Gut Syndrome. For these reasons diagnosis is best carried out by experienced practitioners.  Symptoms of a food intolerance include gas, intermittent diarrhea, constipation, irritable bowel syndrome, skin rashes, migraine headaches, and an unproductive cough.

# Food Intolerance (Chemical Sensitivity)
Reactions to chemical components of the diet are more common than true food allergies. They are caused by various organic chemicals occurring naturally in a wide variety of plant and other foods. Also, and more commonly recognised, by additives, preservatives, colourings and flavourings added to foods in preparation. Both natural and artificial ingredients may cause adverse reactions in sensitive people if consumed in sufficient amount, the degree of sensitivity varying between individuals. Reactions to natural food chemicals are more frequent and more insidious as they can be more difficult to diagnose.
Chemical  intolerance can occur in individuals from both allergic and non-allergic family backgrounds. Symptoms can occur at any age either suddenly or more gradually. Sometimes a change in diet can trigger it, or as a result of virus infection, or serious illness, particularly when a sudden weight loss is observed. Reactions to drugs and environmental chemical exposure can occasionally be involved. It occurs more commonly in women and may be because of hormone differences, as many food chemicals mimic hormones.
This form of food intolerance can present with symptoms affecting the skin, respiratory tract,  gastrointestinal tract (GIT), central nervous system (CNS) either individually or in combination.  
The best recognised symptoms include urticaria, angioedema, migraine or headaches, irritable bowel syndrome.
Respiratory tract symptoms can include nasal congestion, sinusitis, pharyngeal irritations and asthma.
GIT symptoms include mouth ulcers,  abdominal cramp, nausea, bloating, diarrhoea, constipation or irregular bowel movement and gas.
CNS symptoms can be bizarre resulting in patients being labelled neurotic or hysterical if food intolerance is not recognised, headache, lethargy, and myalgia are common but also memory loss, concentration difficulty, mental agitation, depression, dysphasia, visual disturbances, dizziness, tinnitus,  autonomic disturbances, paraesthesias and neuralgias.
Some other commonly reported symptoms include fatigue, sudden loss of energy or chronic lack of energy.
Note that CNS and these symptoms can be caused otherwise, making diagnosis difficult.
The most widely distributed natural food chemical capable of provoking reactions is salicylate containing foods, cross reactions with tartrazine and benzoic acid are well recognised. However it is not widely recognised that significant amounts of benzoates and salicylates occur naturally in many different foods including fruits, juices, vegetables, spices, herbs,  nuts, tea, wines, and coffee. Other natural chemicals which commonly cause reactions and cross reactivity include amines, monosodium glutamate (MSG), nitrates and some anti-oxidants. Chemicals involved in aroma and flavour are often suspect.
It should be noted that classification or avoidance of foods based on botanical families bears no relationship to their chemical content and is not relevant in  the management of food intolerance.
Salicylate containing foods include apples, citrus fruits, strawberries,  tomatoes, and wine, however reactions to chocolate, cheese,  bananas, avocado, tomato and wine point to amines as the likely food chemical. Thus exclusion of single foods does not necessarily identify the chemical responsible as several chemicals can be present in a food and many are sensitive to a number of food chemicals and reaction more likely to occur when foods are eaten in combination that exceed sensitivity thresholds. Others may be more sensitive and react to tiny amounts. 

## Weight Management, Metabolism and Fluid Retention
Food intolerance can cause fluid retention as an offending food appears to increase the permeability of the capillaries or fine blood vessels and extra water enters the cells making them swell. Or sometimes bloating can be a sign of fluid retention or that the GI is not dealing properly with a certain food, in both cases excess weight is the result.
Ongoing research is linking food intolerance and bad digestion to a slower metabolism.

## Diagnosis, Treatment and Management
Diagnosis can include elimination and challenge testing, clinical investigation is generally undertaken only for more serious cases, as for minor complaints not affecting lifestyle the cure may be more inconvenient than the problem. Treatment can involve avoidance, and re-establishing a level of tolerance.
Individuals can try minor changes of diet to exclude foods causing obvious reactions, and for many this may be adequate without the need for professional assistance. For reasons mentioned above foods causing problems may not be so obvious. Persons unable to isolate foods and those more sensitive or with disabling symptoms should seek expert medical and dietitian help. The dietetic departments of teaching hospitals is a good start. (see links below)
Guidance can also be given to your general practitioner to assist in diagnosis and management. Food Elimination Diets have been designed to exclude food chemicals likely to cause reactions and foods commonly causing true allergy problems and those foods where enzyme deficiency cause symptoms.  These elimination diets are not every day diets but intended to isolate problem foods and chemicals. Avoidance of foods with additives is also essential in this process.
Individuals and practitioners need to be aware that during the elimination process patients can display aspects of food addiction, masking, withdrawals, and further sensitization and intolerance.
Those foods that an individual considers a 'must have everyday' are suspect
addictions, this does include tea, coffee, chocolate and health foods and drinks, as they all contain food chemicals.  Individuals are also unlikely to associate foods causing problems because of masking. Where separation of time between eating and symptoms occur. The elimination process can overcome addiction and unmask problem foods so that the patients can associate cause and effect.
It takes around 5 days of total abstinence to unmask a food/chemical, during the first week on an elimination diet withdrawal symptoms can occur but it takes at least 2 weeks to remove residual traces. If symptoms have not subsided after 6 weeks, food intolerance is unlikely involved and a normal diet should be restarted. Withdrawals are often associated with a lowering of the threshold for sensitivity which assists in challenge testing, but in this period individuals can be ultra sensitive even to food smells so care must be taken to avoid all exposures.
After 2 or more weeks if the symptoms have reduced considerably or gone for at least 5 days then challenge testing can begin. This can be carried out with selected foods containing only one food chemical, so as to isolate it if reactions occur. In some countries such as Australia purified food chemicals in capsule form are available to doctors for patient testing, these are often combined with placebo capsules for control purposes. (see link below) This type of challenge is more definitive. New challenges should only be given after 48 hours if no reactions occur. Or after 5 days of no symptoms if reactions occur.
Over a period of time it is possible for individuals avoiding food chemicals to build up a level of resistance by regular exposure to small amounts in a controlled way, but care must be taken, the aim being to build up a varied diet with adequate composition.

### IgG Blood Tests
The food intolerance IgG blood test detects the antibody reactions in the blood. A tiny sample of blood is required, sometimes using a pinprick instead of a syringe. The presence of a food specific IgG antibody indicates that the body has a reaction to this specific food item and depending how high the IgG's are the test can tell the level of the individual's intolerance to this food.
Once all food chemicals are identified  a dietitian or a healthcare professional can prescribe an appropriate diet for the individual to avoid foods with those chemicals. Lists of suitable foods are available from various hospitals and patient support groups can give local food brand advice. A dietitian will ensure adequate nutrition is achieved with safe foods and supplements if need be.
Shown below is an example of IgG blood tests, courtesy of Dr. Dayana Davidis.
It is common for individuals that are intolerant to certain foods to develop an intolerance to other foods with a similar molecular structure or a similar protein structure. This is known as cross reactivity. This would mean that the person suffering from symptoms that are caused by certain food intolerances would still suffer from the same symptoms even while avoiding these foods. The most common food cross reactivity are between the legumes and between the apple and birch pollen, for example if a person has reacted to peanuts, he or she might develop an intolerance to chickpeas or lentils as they all belong to the same family of legumes.
Shown Below is an example of an interpretation of an IgG food intolerance test, courtesy of Dr. Dayana Davidis.