Food intolerance presents classically with flatulence, bloating, fatigue, vomiting, abdominal cramps, and diarrhea [9]. Rare symptoms include hives, migraine headache, wheezing, and difficulty in breathing. Symptoms are much severer in food allergy. Also unlike food allergy, symptoms are not immediate and they emerge only after the consumption of large amounts of the food.

In lactose intolerance, lactose sugar, which is found in cow's milk, passes undigested to the colon, raising the luminal osmolarity, causing abdominal bloating, discomfort, flatulence, and diarrhea.

However, in some cases, the trigger factor of the food intolerance is unknown. Symptoms vary in severity and may occur if the food items are ingested in excess. Fatty foods are responsible for intolerance in some individuals.

These symptoms are similar to those of certain GI diseases such an irritable bowel syndrome, which should hence be excluded.

Diagnosis of food intolerance is essentially clinical and laboratory investigations are rarely needed. However, in some cases where doubts arise, a food allergy needs to be excluded through skin allergy tests and serum IgE levels.

The diagnosis of lactase deficiency or lactose intolerance may require certain special tests, such as hydrogen breath tests and milk intolerance tests.

It is essential to note that self-diagnosis and uninformed avoidance of supposed food triggers are not recommended, as it may lead to nutritional deficiencies and masking of a more severe underlying gastrointestinal disease.

Diagnosis of food intolerance should be confirmed by a healthcare professional. Food intolerance can be diagnosed from the history. Also, when the suspected food is eliminated from the diet symptoms tends to disappear, while its re-institution induces the re-initiation of these symptoms.

Specific treatment plans are currently unavailable because of the limited knowledge on the mechanism behind food intolerance. However, the mainstay of treatment of food intolerance is dietary restriction. Patients are required to identify and avoid or reduce the intake of the dietary triggers for a period of about 4 weeks to achieve symptomatic relief.

Lactase-free products may be considered in cases of patients with lactose intolerance. However, in lactose intolerance, whole milk may be well tolerated. Additionally, lactase enzyme preparations are available for use as an adjunct treatment for symptomatic relief in lactose intolerance. Lactose can be found in a lot of medications and several other foods besides the well-known lactose-containing foods. These foods with hidden lactose include curd and non-fat dry milk powder, hence patients are advised to check labels of drugs and food items before purchasing or consuming them. Calcium supplementation is necessary for all patients who are treated for lactose deficiency by eliminating dairy products from their diet.

Patient education would consist of providing information about alternative diets to ensure adequate nutrition. The food is gradually reintroduced to prevent nutritional deficiencies and because prolonged avoidance or elimination of the diet restores tolerance to the food. Probiotics may also be employed as a useful adjunct treatment for most GI symptoms [10].

Food intolerance is often self-limited. Symptoms fail to recur in children if they are re-exposed to the offending food after a couple of years of avoiding them. Food intolerance is generally not fatal, unlike food allergies which may be life-threatening.

Food intolerance typically results from certain constituents of foods which have properties that trigger gastrointestinal symptoms. These constituents include salicylates, glutamates, caffeine, and vasoactive amines such as histamines.

Short-chain fermentable carbohydrates are particularly implicated in the induction of GI-related symptoms. These carbohydrates are generally termed fermentable oligo-, di-, monosaccharides and polyols (FODMAPs). These substances have been associated with increased GI symptoms in individuals with predisposing diseases such as inflammatory bowel syndrome. Avoiding all foods under the group causes significant improvement in symptoms [5] [6] [7].

A very common form of food intolerance is lactose intolerance which occurs due to the inability of the small intestinal cells to produce lactase. This results in an inability of lactose hydrolyzation or breakdown into its simpler constituent: glucose and galactose. These monosaccharides are the only absorbable forms of lactose. Lactose is contained in milk and processed dairy products. Lactase deficiency may be a genetic disorder or an acquired problem secondary to GI pathologies which cause the destruction of the intestinal mucosa. Diseases which cause acquired lactase deficiency include gastroenteritis, Whipple's disease, inflammatory bowel diseases, and celiac disease.

Salicylate intolerance is another form of food intolerance in certain people. Salicylates are naturally found in plants as a protective substance. Foods rich in salicylates include vegetables and fruits.

Food additives have also been implicated in a few cases of food intolerance. Common offending food additives include MSG, nitrates, and sulfites. Sulfites are additives in alcoholic beverages and are responsible for some cases of intolerance to alcohol and wine.

Non-celiac gluten sensitivity is a novel diagnosis which is nonimmune-mediated, as opposed to celiac disease.

Food intolerance occurs in up to 20% of the population. However, it may be more predominant in certain ethnic groups.

Whereas lactose intolerance is least commonly found in northern Europeans, it is most commonly found among Asian-Americans and African-Americans with an incidence rate of 90% and 75% respectively. Nonetheless, lactase deficiency affects persons of all races and has no gender predilections.

Food intolerance may result from defects in digestive enzymes, GI effects of certain substances such as vasoactive amines found in foods, metabolic and other GI abnormalities [8].

In lactose intolerance, undigested lactose moves into the colon where it induces an osmotic gradient which causes transfer of fluids and electrolytes into the intestinal lumen. This colonic distension results in increased intestinal peristalsis which, coupled with the high colonic osmolarity, accounts for all the GI symptoms.

FODMAPs are particularly implicated in the pathogenesis of food intolerance. Fructose, for example, is a monosaccharide found naturally in fruits and honey. It is found in high amounts in corn syrups. GI absorption of fructose is restricted, determined exclusively by the facilitated transports present. The most common routes of carbohydrate transports are the glucose transporters (GLUT) 2 and 5. Glucose and fructose are transported in equal proportions via the GLUT-2 in the luminal surface of the intestinal mucosa. Other transporters have not been so extensively studied. Diets containing excess fructose trigger GI symptoms by interfering with the absorption of glucose, this results in an increased osmolarity, causing GI distress.

Fructans are short-chain sugars with low GI absorptive properties, due to the absence of the enzymes to break them down. Polyols, also called sugar alcohols, include sorbitol, xylitol, and mannitol. Polyols are found as natural components of certain fruits including apricots, apples, cherries, peaches, pears and vegetables such as cauliflower and mushrooms. They are also used industrially as artificial food sweeteners and in pharmaceutical industries for making sugar-free cough syrup. They are absorbed passively in the small intestine at varying rates, depending on the size of the molecular mass of the polyol, the size of the intestinal pore, the intestinal transit time, and a preexisting gastrointestinal pathology. Absorption of mannitol is better than that of sorbitol. This may be attributed to a higher water solubility and its hydroxyl group.

Food intolerance can be prevented by keeping a list of the offending foods and avoiding their intake.

Food intolerance is a non-IgE-mediated hypersensitivity to food. Food intolerance is similar in symptomatology to food allergy, presenting with vomiting, diarrhea, flatulence, abdominal cramps, and nausea.

The pathophysiologic mechanism behind food intolerance is largely unknown, however, it could be caused by genetic or acquired enzyme deficiencies, osmotic food components such as sugars, and additives including sulfites, histamines, and monosodium glutamate (MSG). Lactose intolerance is a very common cause of food intolerance and it results from lactase deficiency, the enzyme necessary to digest lactose. These symptoms of lactose intolerance typically occur within 2 hours of ingesting lactose-containing foods, such as cheese and ice cream. The symptoms reflect the amount of lactose ingested [1] [2] [3] [4].

Certain sugars induce osmotic diarrhea if poorly absorbed and foods containing fructose and sorbitol are the commonest cause of food intolerance. The sugars are poorly absorbed in the small intestine; often due to the impaired breakdown into their absorbable forms, they present in the colon where they are fermented by colonic bacteria. These products of bacterial breakdown cause flatulence and other symptoms of intolerance. Foods containing monosodium glutamate (MSG) and histamines are also implicated in a few cases of food intolerance.

Food additives are considered as triggers of certain food intolerances such as wine intolerance.

Diagnosis of food intolerance is largely from the history and by elimination or diagnostic diet, where elimination of the offending food classically causes relief of symptoms and vice versa. Although the history can distinguish food allergy from food intolerance, a skin allergy test may be done in some cases to exclude allergy.

Food intolerance is treated by avoidance of the offending food in the diet.

Food intolerance is quite different from a food allergy, although both conditions present similarly. Notable differences are the lack of involvement of the immune system, absence of allergic reactions, and the negative allergy testing in food intolerance. Therefore, food intolerance refers to a non-allergic sensitivity to certain foods.

Food intolerance may be caused by deficiencies of the necessary digestive enzymes or the properties of a food responsible for causing GI upset. Some individuals are born with this enzyme deficiency, while others acquire it as they age. Lactose intolerance and alcohol intolerance are examples of food intolerance caused by the unavailability of digestive enzymes. However, the mechanism of most forms of food intolerance is largely unknown.

Lactose intolerance may result from a genetic absence of lactase or from intestinal diseases, which destroy the intestinal cells which produce lactase. These diseases include gastroenteritis and inflammatory bowel diseases.

Unlike celiac disease, which is a response to gluten in foods mediated by the immune system, non-celiac gluten intolerance is a non-allergic response to gluten in the diet and has been shown to exist. This novel diagnosis is a common cause of food intolerance. Examples of gluten-containing foods include wheat and cereals.

A few individuals display intolerance to wine and preserved foods, this is due to the sensitivity of these individuals to the additives in these foods. Alcoholic beverages contain an additive called sulfite, which is responsible for most cases of wine intolerance experienced by some persons.

Food intolerance typically presents with nausea, vomiting, abdominal cramps, diarrhea, flatulence, and weight loss. These symptoms of food intolerance occur after the ingestion of large quantities of the offending food and do not occur immediately. These are contrary to the case of a food allergy, where the symptoms occur upon the ingestion of a little amount of the food and occur immediately after ingestion

Food intolerance is generally self-limited and resolves when the offending food is avoided; food allergy, on the other hand, may be life-threatening due to the significant breathing difficulties associated with it. A diagnosis of food intolerance is made from the history and the characteristic absence of symptoms once the foods are eliminated. Skin allergy tests and blood tests may be done to exclude food allergy.

The treatment of food intolerance basically involves the elimination of the offending food, while taking alternatives of similar nutritional value. However, tolerance can be achieved again when the food is reintroduced after a long time, however, reintroduction has to be done in smaller quantities.

Patients who have lactose intolerance should check the labels of foods and drugs well before consuming them because some of these items may have lactose hidden in them. Because patients with lactose intolerance may avoid diary products as a way of testing the condition, calcium supplements are necessary to provide an alternative source of calcium for the body.

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