Food allergies and reactions can be confusing. Often, it's not easy to figure out which foods contain ingredients that may trigger a reaction. Further, many people who think they are allergic to a food may actually be confusing a food reaction for an allergy -- and may not need to eliminate certain foods.
WebMD turned to Stanley Cohen, MD, for answers to common questions about food allergies. He's a specialist in pediatric gastroenterology and nutrition, and author of Healthy Babies, Happy Kids: a Common Sense Guide to Nutrition for Growing Years.
What is a food allergy?
A food allergy is a predictable reaction to a specific food or food group. An allergy is caused by an immune reaction to the protein in a food, which brings about a sudden release of chemicals that cause the symptoms.
Symptoms typically appear within a few minutes to two hours of consuming the food. They can range from mild -- like a rash, itching, or swelling -- to life-threatening, including breathing difficulties and swelling of the throat or tongue. Many people with severe allergies carry an epinephrine pen, a self-injectable device to help counteract the allergic reaction and give them time to get emergency medical attention.
Many children and adults will start with a single allergy, and then develop others. Some even "lose" their allergy over time. If you are allergic to milk protein, you may also be allergic to other kinds of milk protein, like goats' milk and soy beverages.
What are the most common food allergies?
Eight foods account for 90% of all food allergy reactions: milk, eggs, peanuts, tree nuts, soy, wheat, shellfish, and fish.
In older children and adults, fish, peanuts, shellfish, and tree nuts are the most common allergies. These allergies are also considered the most serious, because they can be life-threatening.
If you are trying to avoid allergenic foods, what should you look for on food labels?
It is essential that you become an avid label reader. Start at the list of ingredients, which is where you will find the clues to what is contained within the product.
Become familiar with all the food terms for your specific allergy. For example, if you are allergic to milk protein, you need to avoid all foods made from milk, including cheese, yogurt, half-and-half, and cream. Avoid all foods that contain whey, casein, caseinate, nonfat milk solids, lactoglobulin, cow's milk protein, nougat, curds, sodium caseinate, or lactalbumin. Look carefully at butter, margarine, ice cream, cakes, puddings, sorbet, breads, soups, vegetables with sauces, and more.
People with allergies would benefit from a diet that is less processed and closer to natural foods, because there are fewer additives in these foods that could cause problems.
How are allergies diagnosed?
There are several ways to confirm an allergy. First is the old-fashioned prick test, where the skin is scratched with the allergen and observed for reactions. The second is the patch test, which is similar to the prick test, and the last are specific food allergy blood tests. In all of these tests, there is a possibility for false positives and negatives, so physicians usually try an elimination diet, in which the suspected food is avoided. This is followed by a food challenge in which the suspected food is reintroduced under careful observation on three separate occasions to confirm the allergy.
How do you treat allergies?
At this time, there are no medications that cure food allergies. The most important treatment is the elimination of the allergy-causing food. Careful reading of ingredient labels is essential to avoiding all foods with the allergy-causing ingredient. For example, milk may be listed by its components casein or whey, and eggs can be labeled as albumin. If you have an allergy to a certain food, you must become familiar with all related ingredients that could potentially cause a reaction. A good rule of thumb is, when in doubt, don't eat it.
Evolving research suggests that certain probiotics ("friendly" bacteria) may help to prevent or moderate the effects of some allergies. Consult your physician to determine if you might benefit from including probiotics in your diet.
What is the difference between an intolerance and an allergy?
Most people think the terms "food allergy" and "food intolerance" mean the same thing. Yet a food intolerance or reaction does not involve the immune system and can involve components of the food other than proteins. Milk or dairy is a good example in which many people confuse an allergy with intolerance. A milk allergy can only occur if the individual is allergic to the milk proteins (casein, whey, or lactalbumin). Intolerance to milk is caused by an inability or reduced ability to digest the milk carbohydrate (lactose), and results in diarrhea, bloating, gas, pain but no vomiting or rash.
Other common food intolerances are to wheat and corn products. Approximately 33% of adults and 6%-8% of children have had some kind of intolerance or adverse food reaction.
Can intolerances be diagnosed with a medical laboratory test?
If you suspect you are lactose-intolerant, your doctor can give you a hydrogen breath test to verify the condition. Blood tests can confirm a gluten intolerance. Eliminating suspected foods, then reintroducing them in a planned way, helps confirm a diagnosis of food intolerance.
Is it true that people with lactose intolerance can tolerate some dairy products?
Yes, but they need to proceed cautiously to determine that it is an intolerance, and not an allergy. If you have some degree of tolerance to dairy, test your limits by consuming small portions at meals and watch for symptoms. Good choices for this kind of testing are aged cheeses and yogurts with active cultures, which have less lactose. Other options are to drink milk that contains predigested lactose, or take an enzyme that aids in lactose digestion. Keep in mind that dairy is sometimes not well-tolerated immediately following a bout of gastroenteritis, but this is only temporary.
If you suspect your child has an allergy, what should you do?
For a few weeks, keep a diary of everything your child eats and at what time, any symptoms, and what time symptoms appear. Keeping a symptom diary will help you and your physician identify food triggers or patterns. Take into consideration any emotional factors in your child's life, such as stress, or whether the symptoms only occur on school days, or every time they have a baseball game or a visit with a stepparent.
Is there anything parents can do to keep children from developing allergies?
The cause of food allergies is not fully understood, yet there appears to be a hereditary association. Children are 20% more likely to develop allergies if one of their parents has the allergy, and 40% more likely if both parents are allergic.
Some experts think an early introduction to the highly allergic foods may be beneficial in breastfed babies. Introduction should occur slowly, between 4 and 6 months of age, with only one new food a week, and parents must be vigilant in watching for symptoms. It's recommended that you check with your doctor before introducing these foods.
What precautions should allergic moms take when feeding their newborns?
Breastfeeding is best. Protein hydrolysate infant formulas are the recommended formula for allergic infants. When you start introducing foods, only introduce one new food a week, starting with rice cereal or vegetables and ending with eggs. Be very cautious with egg whites, since they are highly allergenic in infants. Preferably, introduce them in the presence of your physician.
Can children outgrow food allergies?
Most allergies start in childhood, but not all. What is fascinating is that some kids outgrow their allergies and begin tolerating the protein by 5 years old if they avoid the offending foods when they are young. In the case of milk allergy, this occurs primarily in infants and toddlers, and many outgrow it by the age of 3.
However, allergies to peanuts, tree nuts, fish, and shellfish tend to be lifelong.
Why are wheat allergies and gluten intolerance on the rise?
More cases are being identified because we have better screening tools. It is now estimated that one in 133 people have a wheat allergy to the gluten (protein); previously we thought only one in 5,000 had the allergy.
What precautions should you take if you suspect you are gluten-intolerant?
Gluten is a combination of starch and protein found primarily in wheat, barley, rye, and spelt. It is used extensively in our food supply as a thickening agent and filler, and can be found in minute amounts in foods ranging from ketchup to ice cream.
A growing number of people feel they have difficulty digesting gluten, or blame gluten for other conditions. Grains that are well-tolerated for gluten-sensitive individuals are corn, rice, potatoes, buckwheat, amaranth, quinoa, and sorghum. Legumes are a high-fiber, high-protein option that can be used as a grain substitute.
If you feel you are not tolerating gluten, read labels carefully to avoid products made from wheat, barley, bulgur, matzo, rye, spelt, graham flour, semolina, farina, triticale, durum, gluten, gliadin, and couscous and everything that is made from these products.
Any suggestions for eating out with allergies?
Eating out is a challenge when you have allergies, because you don't know exactly what is in the food you order. Ask lots of questions of the server to better understand the contents of your favorite dishes, and frequent those restaurants where you find foods that are prepared without offending foods.
In general, ordering simply prepared foods is your best bet. Go for grilled or roasted meats, and fish or chicken without flour coatings. Steamed vegetables, baked potatoes, plain rice, and fruit are other dishes that should be well-tolerated.
Can you develop an allergy to a food that you once tolerated?
Yes, but perhaps more commonly, you may have been allergic but because of a limited exposure to the food you may have not recognized the food reaction symptoms. For example you may not have linked a skin rash to your diet, but it could be a symptom of an allergy. Or, if you typically don't eat much shellfish, you might not know you have an allergy until you eat a large portion.
If you are eliminate certain foods or food groups due to allergies or intolerances, should you be concerned about missing nutrients?
Absolutely. All of my patients work with a registered dietitian to ensure the missing nutrients from the eliminated food is supplied by other foods or dietary supplements. This is especially important when there are multiple allergies or when dairy is limited or eliminated, because it is the best source of calcium in the diet.