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Food Allergies and Intolerance, and Special Diets

Food Allergies
Food Intolerance


Many Americans have experienced adverse reactions after eating certain foods. A food allergy is an adverse reaction to a food or food component, and involves the body's immune system. Some adverse reactions to foods involve the body's metabolism but not the immune system. These reactions are known as food intolerance. It is important, as with any illness, allergy or medical problem, that you seek a medical professional if you think that you might have a food allergy or intolerance. [1] [ To Top ]

Food Allergies

Surveys have shown that approximately one in three adults believe they have a food allergy.  In reality, however, less than two percent of adults (approximately 5 million Americans) actually have food allergies. With food allergies, people tend to diagnose themselves and think that they are having allergic reactions to certain foods or food ingredients. However, self-diagnosis can lead to unnecessary food restrictions.  The in correct diagnosis of a food allergy can be life threatening, because symptoms that occur after eating are often mistaken for a food allergy, but could instead be indicative of another, more severe, medical condition. Experts urge people to see a board-certified allergist for proper diagnosis of food allergy [2]

What is an allergic reaction?[3]

An allergic reaction involves two features of the human immune response. One is the production of immunoglobulin E (IgE), a type of protein called an antibody that circulates through the blood. The other is the mast cell, a specific cell that occurs in all body tissues but is especially common in areas of the body that are typical sites of allergic reactions, including the nose and throat, lungs, skin, and gastrointestinal tract.

The body's immune system recognizes an allergen in the food as "foreign" and produces antibodies to stop the invasion of the allergen. As the battle between the antibodies and the allergens continues, symptoms appear throughout the body, most commonly the mouth, digestive tract, skin, and the airways. Some symptoms include the swelling of the lips, stomach cramps, vomiting diarrhea, hives, rashes, wheezing or breathing problems [4]

Allergic reactions to food are rare and can be caused by any food. However, the most common foods that people are allergic to are:

  • fish
  • shellfish
  • milk
  • eggs
  • soy products
  • wheat
  • peanuts, and;
  • tree nuts (such as walnuts)[5]

Food allergy symptoms can vary, but they usually begin within minutes to a few hours after eating the allergen [6]

Food Additives and Preservatives

There are misconceptions regarding allergy to food additives and preservatives.  Some additives and preservatives trigger asthma or hives, but these reactions are not  involved with the immune system, making them examples of food intolerance rather than food allergy. Most Americans consume a wide variety of food additives daily, with only a small number of additives and preservatives being associated with negative reactions [7]

Life-Threatening Reactions

A small percentage of individuals with a food allergy have a severe reaction to the offending allergen, called anaphylaxis.  ANAPHYLAXIS is a rare, but a potentially life threatening condition in which several different parts of the body experience food-allergic reactions simultaneously, causing hives, swelling of the throat and difficulty breathing. Symptoms of ANAPHYLAXIS usually occur within minutes of exposure to the allergen. Because the symptoms can be life threatening, immediate medical attention is necessary when an anaphylactic reaction occurs. Standard emergency treatment often includes an injection of epinephrine (adrenaline) to open up the airway and blood vessels.  If you see someone undergoing anaphylaxis, call 911 immediately.[8]

Diagnosis and Management

For a true diagnosis of a food allergy, doctors use food allergy skin tests, in which the skin on the arm or back is pricked and a food solution extract is placed on the pricked areas. About 15 minutes after the extract is placed on the skin, the area is checked for a reaction that indicates an allergic response.  Additional medical history, as well as food journals that some people are advised to keep, are thoroughly examined to rule out underlying medical conditions that are not related to food allergy[9]

If a food allergy is diagnosed, the most proven treatment is avoidance of the offending food. Because there are no drugs or allergy shots available to alter the long-term course of food allergy, elimination diets the best prescription. Each diet must consider the individual's nutritional needs, including the ability to tolerate the offending food, caloric needs and other factors. Strict adherence to an elimination diet and carefully avoiding the food allergen may, in some cases, cause the disappearance of the food allergy[10] If you have been diagnosed with a food allergy and adhere to a strict elimination diet, it is important that you speak to your college or university's dining services about the ingredients of their food.  Also, check out whether the dining service on your campus would be able to make special meals that accommodate your dietary needs.

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Food Intolerance

Food intolerance is often confused with food allergies. While a food allergy is an adverse reaction involving the body's immune system, food intolerance involves the body's metabolism[11]

Lactose Intolerance

The most common food intolerance is lactase deficiency, also known as lactose intolerance. This food intolerance affects at least one out of ten people. Lactase is an enzyme that is in the lining of the gut. This enzyme degrades lactose, which is in milk. If a person does not have enough lactase, the body cannot digest the lactose in most milk products. Instead, the lactose is used by bacteria, gas is formed, and the person experiences bloating, abdominal pain, and sometimes diarrhea[12]

Symptoms and Causes

Common symptoms of lactose intolerance include:

  • nausea
  • cramps
  • bloating
  • gas
  • diarrhea

Symptoms begin about 30 minutes to 2 hours after eating or drinking foods containing lactose. The severity of symptoms varies depending on the amount of lactose each individual can tolerate[13]

Some causes of lactose intolerance are well known. For most people, lactase deficiency is a condition that develops naturally over time. After about the age of 2 years, the body begins to produce less lactase. However, many people may not experience symptoms until they are much older[14]


The most common tests used to measure the absorption of lactose in the digestive system are the lactose tolerance test, the hydrogen breath test, andthe stool acidity test.  These tests are performed on an outpatient basis at a hospital, clinic, or doctor's office [15]

The lactose tolerance test begins with the individual fasting (not eating) before the test and then drinking a liquid that contains lactose. Several blood samples are taken over a 2-hour period to measure the person's blood glucose (blood sugar) level, which indicates how well the body is able to digest lactose. If the blood glucose level is not normal, a diagnosis of lactose intolerance may be confirmed[16].

The hydrogen breath test measures the amount of hydrogen in the breath. Normally, very little hydrogen is detectable in the breath. However, bacteria and gasses ferment undigested lactose in the colon, including hydrogen, are produced. In this test, the patient drinks a lactose-loaded beverage, and the breath is analyzed at regular intervals. Raised levels of hydrogen in the breath indicate improper digestion of lactose. Certain foods, medications, and cigarettes can affect the test's accuracy and should be avoided before taking the test[17]

If necessary, a stool acidity test, which measures the amount of acid in the stool, may be given. Undigested lactose fermented by bacteria in the colon creates acids that can be detected in a stool sample. In addition, glucose may be present in the sample as a result of unabsorbed lactose in the colon[18]

Treatment and Management

Fortunately, lactose intolerance is relatively easy to treat. No treatment exists to improve the body's ability to produce lactase, but symptoms can be controlled through diet. Most adults need not avoid lactose completely, but individuals differ in the amounts of lactose they can handle. For example, one person may suffer symptoms after drinking a small glass of milk, while another can drink one glass but not two. Others may be able to manage ice cream and aged cheeses, such as cheddar and Swiss but not other dairy products. Dietary control of lactose intolerance depends on each person's learning through trial and error how much lactose she can handle [19]

For those who react to very small amounts of lactose or have trouble limiting their intake of foods that contain lactose, lactase enzymes are available for purchase without a prescription. It is always a good idea to check with your doctor, though, before starting to take over-the-counter remedies to treat a condition.  Alternatively, lactose-reduced milk and other products are available at many supermarkets. The milk contains all of the nutrients found in regular milk and remains fresh for about the same length of time or longer if it is super-pasteurized. Soy products and rice milk are other alternatives to dairy products [20]

Milk and other dairy products are a major source of nutrients in the American diet. The most important of these nutrients is calcium. Calcium is essential for the growth and repair of bones throughout life. In the middle and later years, a shortage of calcium may lead to osteoporosis. A concern, then, for adults with lactose intolerance, is getting enough calcium in a diet that includes little or no milk.

Many nondairy foods are high in calcium. Green vegetables, such as broccoli and kale, and fish with soft, edible bones, such as salmon and sardines, are excellent sources of calcium. To help in planning a high-calcium and low-lactose diet, figure 1 lists some common foods that are good sources of dietary calcium and shows about how much lactose the foods contain. Recent research shows that yogurt may be a good source of calcium for many people with lactose intolerance, even though it is fairly high in lactose. Evidence shows that yogurt has some of the lactase enzyme required for proper digestion [21]

Figure 1

Even though lactose intolerance is widespread, it need not pose a serious threat to good health. People who have trouble digesting lactose can learn which dairy products and other foods they can eat without discomfort and which ones they should avoid A carefully chosen diet (with calcium supplements if the doctor or dietitian recommends them) is the key to reducing symptoms and protecting future health[22].

Hidden Lactose

Although milk and foods made from milk are the only natural sources, lactose is often added to prepared foods. People with very low tolerance for lactose should know about the many food products that may contain lactose, even in small amounts. Food products that may contain lactose include:

  • Bread and other baked goods
  • Processed breakfast cereals.
  • Instant potatoes, soups, and breakfast drinks.
  • Margarine.
  • Lunch meats (other than kosher)
  • Salad dressings.
  • Candies and other snacks
  • Mixes for pancakes, biscuits, and cookies [23]

Some products labeled nondairy, such as powdered coffee creamer and whipped toppings, may also include ingredients that are derived from milk and therefore contain lactose. Smart shoppers learn to read food labels with care, looking not only for milk and lactose among the contents but also for such words as whey, curds, milk by-products, dry milk solids, and nonfat dry milk powder. If any of these are listed on a label, the item contains lactose [24]

      In addition, lactose is used as the base for more than 20 percent of prescription drugs and about 6 percent of over-the-counter medicines. Many types of birth control pills, for example, contain lactose, as do some tablets for stomach acid and gas. However, these products typically affect only people with severe lactose intolerance [25]

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