Food allergy, intolerance and the misconceptions around them
A food allergy, a food intolerance and an adverse reaction to food can look alike, so telling them apart takes a diagnostic evaluation, and a food avoided without one can leave the diet short of the nutrients it supplied. Lactose intolerance, the two kinds of gluten intolerance and a child's food allergy each arise in their own way and are diagnosed with their own tests.
Kinds of food sensitivity
According to one registered dietitian, greater awareness of food allergies and intolerances has been accompanied by misconceptions that can lead to adverse health outcomes.
Food sensitivity is the blanket term for all reactions to food, and it covers three types of food reaction. A food allergy is an immune response that occurs reproducibly on repeat exposure to a particular food, specifically to the protein in it; IgE antibodies are produced during the initial exposure to fend off the foreign protein on any later one, and anaphylaxis is possible. A food intolerance is an adverse physiological effect that also occurs reproducibly on repeat exposure, but with no IgE antibodies produced. An adverse reaction is an abnormal response to food caused by bacterial, viral or parasitic infectious contaminants, or by food-borne or water-borne contaminants.
One physician explains that the clinical features of the three can be similar, so she recommends diagnostic evaluation to determine which mechanism is at work. Without it, many people diagnose themselves and unnecessarily avoid entire categories of food, which can cause nutritional deficiencies and other health problems.
Lactose intolerance
Lactose intolerance arises when the villi of the small bowel produce too little lactase, the enzyme that breaks down the milk sugar lactose. The excess sugar then passes to the colon, where gut bacteria break it down for absorption, and in some people this causes abdominal pain, cramping, bloating and diarrhoea. In a 2009 study in Nutrition Today, 12% of adults in the United States reported being lactose intolerant. The prevalence varies by ethnic group: 7.72% among European Americans, 10.05% among Hispanic Americans and 19.50% among African Americans.
One physician stresses that not all such complaints are lactose intolerance, and that diagnostic evaluation needs to recognise the conditions she calls its masqueraders: milk allergy, irritable bowel syndrome, coeliac disease, non-coeliac gluten sensitivity, inflammatory bowel disease such as Crohn's disease and ulcerative colitis, small intestinal bacterial overgrowth, and bowel injury from non-steroidal anti-inflammatory drugs. Lactose intolerance itself is diagnosed with the hydrogen breath test, the gold standard and the least expensive, least invasive and most widely available method.
In a 2011 study in the American Journal of Clinical Nutrition, participants who believed themselves lactose intolerant restricted their dairy intake without eating more non-dairy calcium. One physician holds that it is important to maintain sufficient intake of calcium and dairy foods, and that even patients diagnosed with lactose intolerance do not need to exclude all traces of dairy products from their diet.
Non-coeliac gluten sensitivity and coeliac disease
Gluten is a protein present in many grains, and wheat, rye and barley are the grains typically associated with gluten intolerance. The portion of gluten called gliadin causes the most inflammation in gluten-sensitive people. Gluten intolerance, also known as gluten sensitivity, includes two conditions. Non-coeliac gluten sensitivity is an immune response to ingested gluten that is not autoimmune: gut inflammation is present but the villi of the small bowel are normal, and symptoms improve on a gluten-free diet. Coeliac disease is an autoimmune disease, triggered by ingested gluten, that damages those villi, and a gluten-free diet is required to stop it progressing. Because the villi are damaged, coeliac disease can coexist with lactose intolerance.
Coeliac disease affects 1 in 100 people in the general population, 1 in 56 of those with gastrointestinal symptoms and 1 in 22 of those with a first-degree relative who has the disease. One physician recommends screening for coeliac disease in any patient diagnosed with diarrhoea-predominant irritable bowel syndrome. A fifth of patients with coeliac disease initially have no symptoms. Beyond the non-specific gastrointestinal complaints common to every masquerader, other indicators of possible coeliac disease can include anaemia, osteoporosis, constipation and abnormal liver tests.
Diagnosis of coeliac disease requires compatible clinical symptoms and serological testing. In most cases the same physician recommends the immunoglobulin A tissue transglutaminase blood test, and for the 2% to 3% of the population with IgA deficiency the IgG version. The gold standard is to confirm a positive serological result with a small-bowel biopsy, and genetic testing can be performed where the diagnosis is unclear. In a patient who has already begun a gluten-free diet, serological testing might be negative even if the patient has coeliac disease, but a gluten-challenge diet is no longer recommended for such patients. No medical test can confirm non-coeliac gluten sensitivity, but an elimination diet can be useful.
Even with gluten intolerance confirmed, patients can typically eat other grains and starchy foods, such as amaranth, arrowroot, beans, buckwheat, millet, potato, quinoa, rice and sorghum. Avoiding grains, particularly whole grains fortified with nutrients, has unintended consequences: the loss of complex carbohydrates as an energy source, and deficiencies in fibre, magnesium, selenium, iron, the B vitamins and folic acid.
A child's food allergy, from diagnosis to management
An eight-year-old boy presented with itchy eyes, swollen lips and tongue, sneezing and nausea. On the basis of his medical history, his food diary, a physical examination and his experience with an elimination diet, he underwent laboratory testing: a skin prick test, a radioallergosorbent blood test and a food challenge test. He was diagnosed with allergies to wheat and dairy, which are common in children, as are allergies to eggs, peanuts, soy and tree nuts. In a wheat allergy the reaction is to the albumin and globulin protein fractions, and in a dairy allergy it is to a milk protein such as casein. He had to avoid all milk and milk products and all wheat products and foods made with wheat, but he could safely eat wheat substitutes, including rye and barley.
A registered dietitian advised his family to keep him safe with these strategies:
- Learn which foods contain the allergens and which foods are risky. Most soy sauces, for example, contain wheat. Food and Drug Administration labelling regulations require a "contains wheat" or "contains milk" statement on product labels where applicable.
- Read food labels diligently, and contact food manufacturers with questions.
- Avoid cross-contamination of allergens into allergy-safe food in the kitchen and at the table, for example by using separate containers and utensils for food prepared without the allergens.
- Make recipe substitutions. A cup of wheat flour can be replaced with three-quarters of a cup of rice flour plus a quarter of a cup of cornstarch, and fruit juice or coconut milk can replace regular milk.
- Be just as vigilant away from home, reviewing menus in advance where possible.
- Develop a plan with school staff. Address food substitutes with the food service staff, or have the child eat food prepared at home. Make sure he knows the symptoms of an allergic reaction and what to do about them, such as how to signal for help. Explain to him why swapping food with friends must be avoided, and give him a personal emergency card and his parents' telephone numbers. Plan with the health care provider, other responsible adults and the child himself for giving medication if needed.
Writing about food sensitivities
One registered dietitian urges medical writers to correct misconceptions about food sensitivities, to encourage diagnostic evaluation for gastrointestinal symptoms, and to communicate strategies that help people manage a food sensitivity without compromising good nutrition, health or the enjoyment of eating.