It can be difficult to determine the poorly tolerated substance as reactions can be delayed, dose-dependent, and a particular reaction-causing compound may be found in many foods.
[13] Respiratory tract symptoms can include nasal congestion, sinusitis, pharyngeal irritations, asthma and an unproductive cough.
[13] Food intolerance has been found associated with irritable bowel syndrome and inflammatory bowel disease,[14] chronic constipation,[15] chronic hepatitis C infection,[16] eczema,[17] NSAID intolerance,[18] respiratory complaints,[19] including asthma,[20] rhinitis and headache,[21][22] functional dyspepsia,[23] eosinophilic esophagitis[9] and ear, nose and throat (ENT) illnesses.
[21][24] Reactions to chemical components of the diet may be more common than true food allergies,[citation needed] although there is no evidence to support this.
[27][28] The most widely distributed naturally occurring food chemical capable of provoking reactions is salicylate,[18] although tartrazine and benzoic acid are well recognised in susceptible individuals.
[29][30][31] Benzoates and salicylates occur naturally in many foods, including fruits, juices, vegetables, spices, herbs, nuts, tea, wines, and coffee.
Other natural chemicals which commonly cause reactions and cross reactivity include amines, nitrates, sulphites and some antioxidants.
[41] Non-IgE-mediated intolerance is more chronic, less acute, less obvious in its clinical presentation, and often more difficult to diagnose than allergy, as skin tests and standard immunological studies are not helpful.
Clinical investigation is generally undertaken only for more serious cases, as for minor complaints which do not significantly limit the person's lifestyle the cure may be more inconvenient than the problem.
[46] Diagnosis is made using medical history and cutaneous and serological tests to exclude other causes, but to obtain final confirmation a double blind controlled food challenge must be performed.
The antigen leukocyte cellular antibody test (ALCAT) has been commercially promoted as an alternative, but has not been reliably shown to be of clinical value.
[48][49][50] There is emerging evidence from studies of cord blood that both sensitization and the acquisition of tolerance can begin in pregnancy, however, the window of main danger for sensitization to foods extends prenatally, remaining most critical during early infancy when the immune system and intestinal tract are still maturing.
[citation needed] There is no conclusive evidence to support the restriction of dairy intake in the maternal diet during pregnancy, and this is generally not recommended since the drawbacks in terms of loss of nutrition can out-weigh the benefits.
[51] A Cochrane review has concluded feeding with a soy formula cannot be recommended for prevention of allergy or food intolerance in infants.
[53][54] 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.
Persons unable to isolate foods and those more sensitive or with disabling symptoms should seek expert medical and dietitian help.
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.
[59] A study has demonstrated that identifying and appropriately addressing food sensitivity in IBS patients not previously responding to standard therapy results in a sustained clinical improvement and increased overall well-being and quality of life.
Out of 4,622 subjects with adequately filled-in questionnaires, 84 were included in the study (1.8%) Perceived food intolerance is a common problem with significant nutritional consequences in a population with IBS.
[62] According to the RACP working group, "Though not considered a "cause" of CFS, some patients with chronic fatigue report food intolerances that can exacerbate symptoms.
Using this approach the role played by dietary chemical factors in the pathogenesis of chronic idiopathic urticaria (CIU) was first established and set the stage for future DBPCT trials of such substances in food intolerance studies.
[60] In the Netherlands, patients and their doctors (GPs) have different perceptions of the efficacy of diagnostic and dietary interventions in IBS.
Patients consider food intolerance and GPs regard lack of fibre as the main etiologic dietary factor.
[73] A low-FODMAP diet might help to improve short-term digestive symptoms in adults with irritable bowel syndrome,[77][78][79][80] but its long-term follow-up can have negative effects because it causes a detrimental impact on the gut microbiota and metabolome.
Since the consumption of gluten is suppressed or reduced with a low-FODMAP diet, the improvement of the digestive symptoms with this diet may not be related to the withdrawal of the FODMAPs, but of gluten, indicating the presence of an unrecognized celiac disease, avoiding its diagnosis and correct treatment, with the consequent risk of several serious health complications, including various types of cancer.
[85] A three-month randomized, blinded, controlled trial on people with irritable bowel syndrome found that those who withdrew from the diet the foods to which they had shown an increased IgG antibody response experienced an improvement in their symptoms.
[86] In individuals with Crohn's disease and ulcerative colitis food-specific-IgG-based elimination diets have been shown to be effective at reducing symptoms.
[96][97][98] At present there are a number of ways to limit the increased permeability, but additional studies are required to assess if this approach reduces the prevalence and severity of specific conditions.