symptoms have not subsided after six weeks, food intolerance is unlikely to be 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 two or more weeks if the symptoms have reduced considerably or gone for at least five days then challenge testing can begin. this can be carried out with selected foods containing only one food chemical, to isolate it if reactions occur. in australia, purified food chemicals in capsule form are available to doctors for patient testing. these are often combined with placebo capsules for control purposes. this type of challenge is more definitive. new challenges should only be given after 48 hours if no reactions occur or after five days of no symptoms if reactions occur. once all food chemical sensitivities are identified a dietitian 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. 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. prognosis the prognosis of children diagnosed with intolerance to milk is good: patients respond to diet which excludes cow's milk protein and the majority of patients succeed in forming tolerance. children with non-ige-mediated cows milk intolerance have a good prognosis, whereas children with ige-mediated cows milk allergy in early childhood have a significantly increased risk for persistent allergy, development of other food allergies, asthma and rhinoconjunctivitis. 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. epidemiology estimates of the prevalence of food intolerance vary widely from 2% to over 20% of the population. so far only three prevalence studies in dutch and english adults have been based on double-blind, placebo-controlled food challenges. the reported prevalences of food allergy/intolerance (by questionnaires) were 12% to 19%, whereas the confirmed prevalences varied from 0.8% to 2.4%. for intolerance to food additives the prevalence varied between 0.01 and 0.23%. food intolerance rates were found to be similar in the population in norway. 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. of these 59 (70%) had symptoms related to intake of food, 62% limited or excluded food items from the diet. tests were performed for food allergy and malabsorption, but not for intolerance. there were no associations between the tests for food allergy and malabsorption and perceived food intolerance, among those with ibs. perceived food intolerance was unrelated to musculoskeletal pain and mood disorders. 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." history in 1978 australian researchers published details of an 'exclusion diet' to exclude specific food chemicals from the diet of patients. this provided a basis for challenge with these additives and natural chemicals. 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. in 1995 the european academy of allergology and clinical immunology suggested a classification on the basis of the responsible pathogenetic mechanism; according to this classification, non-toxic reactions can be divided into 'food allergies' when they recognize immunological mechanisms, and 'food intolerances' when there are no immunological implications. reactions secondary to food ingestion are defined generally as 'adverse reactions to food'. in 2003 the nomenclature review committee of the world allergy organization issued a report of revised nomenclature for global use on food allergy and food intolerance, that has had general acceptance. food intolerance is described as a 'non-allergic hypersensitivity' to food. society and culture in the uk, scepticism about food intolerance as a specific condition influenced doctors' perceptions of patients and of the patients' underlying problems. however, rather than risk damaging the doctor-patient relationship, general practitioners (gps) chose - despite their scepticism and guided by an element of awareness of the limitations of modern medicine - to negotiate mutually acceptable ground with patients and with patients' beliefs. as a result, whether due to a placebo effect, a secondary benefit, or a biophysical result of excluding a food from the diet, the gps acknowledge both personal and therapeutic benefits. 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. it has been suggested that dutch gps explore the patients' expectations and potentially incorporate these in their approach to ibs patients. new food labeling regulations were introduced into the us and europe in 2006, which are said to benefit people with intolerances. in general, food-allergic consumers were not satisfied with the current labelling practices. in the usa food companies propose distinguishing between food allergy and food intolerance and use a mechanism-based (i.e., immunoglobulin-e-mediated), acute life-threatening anaphylaxis that is standardized and measurable and reflects the severity of health risk, as the principal inclusion criterion for food allergen labeling. symptoms due to, or exacerbated by, food additives usually involve non-ige-mediated mechanisms (food intolerance) and are usually less severe than those induced by food allergy, but can include anaphylaxis. research directions fodmaps are fermentable oligo-, di-, monosaccharides and polyols, which are poorly absorbed in the small intestine and subsequently fermented by the bacteria in the distal small and proximal large intestine. this is a normal phenomenon, common to everyone. the resultant production of gas potentially results in bloating and flatulence. although fodmaps can produce certain digestive discomfort in some people, not only do they not cause intestinal inflammation, but they avoid it, because they produce beneficial alterations in the intestinal flora that contribute to maintain the good health of the colon. fodmaps are not the cause of irritable bowel syndrome nor other functional gastrointestinal disorders, but rather a person develops symptoms when the underlying bowel response is exaggerated or abnormal. a low-fodmap diet might help to improve short-term digestive symptoms in adults with irritable bowel syndrome, but its long-term follow-up can have negative effects because it causes a detrimental impact on the gut microbiota and metabolome. it should only be used for short periods of time and under the advice of a specialist. more studies are needed to assess the true impact of this diet on health. also, when a low fodmap diet is used without a previous complete medical evaluation can cause serious health risks. it can ameliorate and mask the digestive symptoms of serious diseases, such as celiac disease, inflammatory bowel disease and colon cancer, avoiding their correct diagnosis and therapy. this is especially relevant in the case of celiac disease. 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. 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. in individuals with crohn’s disease and ulcerative colitis food-specific-igg-based elimination diets have been shown to be effective at reducing symptoms. significant presence of food-specific-igg has also been detected jejunostomates, ileostomates, and in individuals with eosinophilic esophagitis or food malabsorption due to intolerance. increased intestinal permeability, so called leaky gut, has been linked to food allergies and some food intolerances. research is currently focussing on specific conditions and effects of certain food constituents. 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.