Chapter 3. Human Body and Digestion

Adverse Food Reactions

Food Allergies

Paying attention to the way individuals react to various foods is essential in determining what foods may specifically affect a person adversely. Food allergies are one of the many ways in which different body make-ups affect nutritional concerns. Although about 6% of young children and 1-2% of adults have food allergies, there are likely many more people who say they have food allergies than actually do. This is because food sensitization is different from a medically-determined food allergy. When someone has a food allergy, the immune system mistakenly attacks a certain kind of food (usually the protein component of a food), such as peanuts, as if it were a threat and IgE antibodies are produced. Doctors sometimes test for food allergies by using skin-prick tests or blood tests to look for the presence of IgE antibodies. However, these types of tests are not always reliable as they can sometimes yield a false positive result. By far, the most valuable tests for determining a food allergy is the Double Blind Placebo Controlled Food Challenge (DBPCFC), which involves administering the food orally and then denoting the signs and symptoms of the allergic response.

Food allergy symptoms usually develop within a few minutes to two hours after a person has eaten a food to which they are allergic. These symptoms can range from the annoying to the potentially fatal, and include:

  • A tingling mouth
  • Swelling tongue and/or throat
  • Difficulty breathing
  • Hives
  • Stomach cramps
  • Diarrhea
  • Vomiting
  • Drop in blood pressure
  • Loss of consciousness
  • Death

There are no clear treatments for food allergies, which are typically life long in adults, whereas children can sometimes outgrow their food allergy through building a tolerance. Epinephrine is sometimes used to control severe reactions, and individuals with known and dangerous allergies may get prescriptions for self-injectable devices. The only certain way to avoid allergic reactions to food is to completely avoid the foods that cause them since even minute quantities of a food allergen can cause a serious reaction. Beyond avoidance, this can mean reading food labels carefully, or even calling manufacturers for product information.

Health Canada and the Canadian Food Inspection Agency have identified the most common food allergens, which are required to be clearly identified on food labels. These priority food allergens are as follows:

  1. Eggs
  2. Milk
  3. Mustard
  4. Peanuts
  5. Crustaceans and molluscs
  6. Fish
  7. Sesame seeds
  8. Soy
  9. Sulphites
  10. Tree Nuts (almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pine nuts, pistachios and walnuts)
  11. Wheat and triticale

Food Intolerance

In contrast to food allergies, a food intolerance is an adverse food reaction that does not involve an immune response. Food intolerances are marked by unpleasant symptoms, such as gastrointestinal upset, but are rarely life threatening. Management involves limiting consumption of the food(s) of concern to varying degrees depending on the severity of the intolerance, whereas food allergies require complete avoidance of the food allergen. Food intolerance occur more often than food allergies, but the two are often confused. Therefore, it is important to get a proper diagnosis from an authorized medical professional if you suspect an adverse food reaction in order to determine the most appropriate form of management.

Lactose intolerance is a common example of a food intolerance. People who suffer from this condition experience an adverse reaction to the lactose in milk products. It is a result of the small intestine’s inability to produce enough of the enzyme lactase, which is produced by the small intestine. Symptoms of lactose intolerance usually affect the GI tract and can include bloating, abdominal pain, gas, nausea, and diarrhea. An intolerance is best managed by making dietary changes and avoiding any foods that trigger the reaction.[1]

Celiac Disease

Celiac disease is an autoimmune disorder affecting about 1% of the Canadian population.[2] It is caused by an abnormal immune reaction of small intestine cells to a type of protein, called gluten. Gluten forms in the presence of water and is composed of two protein parts, glutenin and gliadin. Glutenin and gliadin are found in grains that are commonly used to make bread, such as wheat, rye, and barley. When bread is made, yeast eats the flour and makes a waste product, carbon dioxide, which forms bubbles in the dough. As the dough is kneaded, gluten forms and stretches. The carbon dioxide gas bubbles infiltrate the stretchy gluten, giving bread its porosity and tenderness. For those who are sensitive to gluten, it is good to know that corn, millet, buckwheat, and oats do not contain the proteins that make gluten. However, some people who have celiac disease also may have a response to products containing oats. This is most likely the result of cross-contamination of grains during harvest, storage, packaging, and processing.

Celiac disease is most common in people of European descent and is rare in people of African, Japanese, and Chinese descent. It is much more prevalent in women and in people with Type 1 diabetes, autoimmune thyroid disease, and Down and Turner syndromes. Symptoms can range from mild to severe and can include pale, fatty, loose stools, gastrointestinal upset, abdominal pain, weight loss and, in children, a failure to grow and thrive. The symptoms can appear in infancy or much later in life, even by age seventy. Celiac disease is not always diagnosed because the symptoms may be mild. A large number of people have what is referred to as “silent” or “latent” celiac disease.

Celiac disease diagnosis requires a blood test and a biopsy of the small intestine. Because celiac disease is an autoimmune disease, antibodies produced by white blood cells circulate in the body and can be detected in the blood. When gluten-containing foods are consumed the antibodies attack cells lining the small intestine leading to a destruction of the small villi projections. This tissue damage can be detected with a biopsy, a procedure that removes a portion of tissue from the damaged organ. Villi destruction is what causes many of the symptoms of celiac disease. The destruction of the absorptive surface of the small intestine also results in the malabsorption of nutrients, so that while people with this disease may eat enough, nutrients do not make it to the bloodstream because absorption is reduced. The effects of nutrient malabsorption are most apparent in children and the elderly as they are especially susceptible to nutrient deficiencies. Over time these nutrient deficiencies can cause health problems. Poor absorption of iron and folic acid can cause anemia, which is a decrease in red blood cells. Anemia impairs oxygen transport to all cells in the body. Calcium and vitamin D deficiencies can lead to osteoporosis, a disease in which bones become brittle.

If you think you or someone close to you may have celiac disease, do not despair; it is a very treatable disease. Once diagnosed, a person follows a gluten-free diet for life. This requires dedication and careful detective work to seek out foods with hidden gluten, but some stores carry gluten-free foods. After eliminating gluten from the diet, the tissues of the small intestine rapidly repair themselves and heal in less than six months.

  1. Lactose Intolerance. National Institute of Diabetes and Digestive and Kidney Diseases. Updated June 2014. Accessed December 4, 2017.
  2. Health Canada. Celiac Disease. Published 2018. Accessed July 20, 2019.


Icon for the Creative Commons Attribution 4.0 International License

Human Nutrition Copyright © by Langara College, Nutrition and Food Service Management Program is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Share This Book