Gut Check: Brooks Cash, MD, Joins Dr Brian Lacy to Discuss Food Allergies

Gut Check host Dr Brian Lacy talks with Dr Brooks Cash about food allergies and food sensitivities—what is common, what is rare, and how to tell the difference.

Brian Lacy, MD, is a professor of medicine at the Mayo Clinic in Jacksonville, Florida. Brooks Cash, MD, is division director of  Gastroenterology, Hepatology, and Nutrition at the University of Texas Health Science Center in Houston, Texas, and the Dan and Lillie Sterling Professor of Medicine at University of Texas McGovern Medical School.

TRANSCRIPT:

Dr Brian Lacy:

Welcome to Gut Check, a podcast from the Gastroenterology Learning Network. My name is Brian Lacy. I'm a professor of medicine at the Mayo Clinic in Jacksonville, Florida. I am absolutely delighted to be speaking today with Dr Brooks Cash, professor of medicine and chief of gastroenterology, hepatology, and nutrition at the University of Texas Health Science Center in Houston, Texas. Our topic today is one that routinely comes up in both GI clinics and in primary care, that of food allergies and food sensitivities.

So Dr Cash, welcome. It's such a pleasure to have you back for another Gut Check podcast. Issues with food seem to be so much more common than just 10 or 20 years ago. When you plan a social event these days, it seems as if many, if not most people have an issue with food. So how common are food allergies?

Dr Brooks Cash:

Well, thank you Brian. It's a pleasure to be here. Thanks for having me. And you're right, this is an incredibly common topic that I think is very poorly understood. To answer your specific question, food allergies are quite rare. And we don't have great estimates with regards to the prevalence of food allergies, but the best data that we have would suggest that food allergies affect less than 1% of the population.

Now, when we look at self-reported food allergies, those numbers are typically 3 to 4 times that, so about 4% to 6% of the population feels like they have food allergies. And I think that's part of the issue that you mentioned, is that this is a confusing topic and we really have to be very clear with our definitions. A food allergy is defined as an adverse health event that arises from a specific immune response.

And that's really important to understand, that this is an immune-mediated response. A true allergy that occurs reproducibly on repeated exposure to a given food. Now, a food allergy can affect local areas of the body but it can also affect the entire immune system and cause something like anaphylaxis, which is a systemic immune allergic response. And that can lead to life-threatening allergic reactions. And the prototypical example of that would be a peanut allergy where somebody develops anaphylaxis, airway collapse, and they have difficulty breathing, and that can truly be a life-threatening condition.

However, this is extremely rare. Fatal food anaphylaxis causes about 100 deaths per year in the United States. Not to minimize that, but it is a rare event. Now, we need to contrast that with food sensitivities, as you described them, are also what are called food intolerances. Really the same thing. Now, these are much more common and these are nonimmunologic responses that seem to be initiated by a food or a food component at a dose that's normally tolerated. And these account, really, for most of the adverse food reactions that people have.

Dr Lacy:

Wow. Brooks, we could almost stop right there. You've covered so much ground already. This is wonderful. And for our listeners, you may want to go back and just repeat that again because you've got so much information packed in there. But I like 2 great teaching points there, Brooks. One: these are overreported, and the key thing there is they have to be reproducible symptoms. So thank you. So thinking about these common food allergies, what are the 5 or 6 most common food allergies?

Dr Cash:

Well, the most common... and you're right, it falls into about 6 different food categories. By far the most common is cow's milk allergies, and second would be eggs. But also tree nuts, and peanuts would fit into that category. Soybeans, shellfish, and then certain fruits and vegetables can also cause classic food allergy-related symptoms and syndromes.

Dr Lacy:

Wonderful. So Brooks, you pointed out that this is an immune-mediated event. And so what are the classic symptoms of a true food allergy? Do these symptoms have to occur immediately, or could they even occur hours or days later?

Dr Cash:

They can occur immediately but they can also occur in a delayed fashion, so several hours afterwards. And the classic symptoms are really very broad for true food allergies. Now, of course we're gastroenterologists. We're talking about GI and we're talking about the digestive tract, so there are GI symptoms. And typically these GI symptoms are going to consist of symptoms such as abdominal cramping or abdominal pain, and typically diarrhea in terms of bowel habit changes.

But there are also other systemic effects. And the classic ones would be urticaria, which is basically a fancy word for a rash or hives. Sometimes people can get swelling of their lips. They may feel shortness of breath or a scratchy throat. They may develop wheezing. And these are all symptoms of a true allergic reaction. And those would be the more systemic effects. Sometimes people can get lightheaded, they can get a headache, perhaps even become diaphoretic or sweaty. But the most common symptoms are going to be those GI symptoms and those skin-related symptoms. The more serious symptoms would be if there's any evidence of shortness of breath or difficulty breathing. And those are really the symptoms that we need to be very keyed into with regards to a true food allergy as potentially being life-threatening.

Dr Lacy:

Brooks, wonderful. Thank you. So thinking about the diagnosis, 2 key points right there. One is that you've discussed classic symptoms. Number 2, you already mentioned they have to be reproducible. But what about testing? What's the best test to diagnose a food allergy?

Dr Cash:

Well, this is an area that has a lot of mystique around it. And we all see patients who will come in with their food allergy panel that they've gotten at a practitioner's, and that's usually a long list of a whole bunch of antibodies that they may have to specific foods. And that's really looking at sensitivities, and it's can be very misleading. Most of us have sensitivities or antibodies that our bodies have made to certain constituents of food. And usually these are proteins that are contained within foods.

That is not an adequate way to diagnose a food allergy. The best and the gold standard way to diagnose a food allergy is to do what's called a single blind food challenge. And this should be done in a monitored setting with resuscitation equipment available and epinephrine and monitoring available. And basically what happens is patients, if they identify a specific food type that seems to cause allergic-like reactions or symptoms, they will go in and eat slowly increasing amounts of that specific food and they will be observed for the development of allergic reactions.

And if they become severe, there may have to be an intervention. That's the gold standard. Obviously that's costly, it's cumbersome, it's time-consuming. It may require multiple different trials or challenges. There are also tests. Typical allergy tests like skin prick tests. That's another. Sensitivity tests. Typical allergy testing that many of us got when we were children, looking for seasonal or allergies to pollens and things like that, where you'll have a small amount of an allergen placed into the skin and you look for a skin reaction.

That's more along the lines of that blood sensitivity testing as well. It's not definitive in terms of defining a food allergy. So lots of mystique. The best test is that single blind food challenge, which is cumbersome. And that is usually done in conjunction with an allergy immunology division.

Dr Lacy:

Wonderful. Brooks, thank you so much. And as you pointed out, this has to be done in a monitored setting with epinephrine and resuscitation equipment in case they have this horrible reaction. So let's shift gears. And you've kind of already mentioned this, but thinking about food sensitivity, sometimes called food intolerances. How common are food sensitivities?

Dr Cash:

These are very common. Food sensitivities far outstrip food allergies. When we look at people who have self-identified irritable bowel syndrome, about 60% of them will blame their symptoms in some way, shape, or form on certain foods. And there are truly food sensitivities. And a classic example, and probably the most common example, would be lactose intolerance. We're also starting to recognize that some people have sucrose or table sugar intolerance as well.

And these are issues where the metabolism and the digestion of the sugars, the more complex sugars in those foods, is not performed or completed successfully as it might have been when we were children, or perhaps where some people are even born with these sensitivities. So those are much more common.

And another very common one that people identify is gluten sensitivity. Now, there is a classic... it's not a food allergy, but a classic syndrome called celiac disease, which is an intolerance to gluten. It's an immune-mediated condition where, when people eat wheat, rye, or barley they develop an immune response, it damages the small intestine, and they can have a whole host of symptoms. They can have dermatologic symptoms, they can have GI symptoms, they can have neurologic symptoms. The prevalence of celiac disease is less than 1%. Probably about 0.7% to 0.8%. But there's a syndrome of what's called nonceliac gluten sensitivity where individuals will identify symptoms after ingesting these grains.

And there's no diagnostic test for that. It's completely based on history and repeated exposure, what we call N-of-one studies, which is where an individual patient can challenge themselves and see if they develop symptoms. And the prevalence of nonceliac gluten sensitivity... and I really don't like the term. I think we ought to be using grain sensitivity, because I think it's not just gluten probably that's causing some of these symptoms. It's a real thing. That's been estimated to be perhaps as high as 30% in people with certain GI syndromes like irritable bowel syndrome. And they're convinced they have celiac disease.

And our task is not to necessarily disavow them that they don't have celiac disease, but to talk about these other conditions. And the sensitivity is a real thing for these patients. And the best treatment for that is to avoid ingestion of these different types of grains. Unfortunately we don't have a test, as I mentioned, but it can be managed quite easily in most patients.

Dr Lacy:

Brooks, that's wonderful. So just to complete that list, you've mentioned some of the most common foods that patients are sensitive to. Lactose as an example. Even sucrose, and of course wheat. We all hear that many people feel that they're sensitive to wheat but not truly allergic to it, and they don't have celiac disease. At least in your experience, what are some of the other most common food sensitivities or food intolerances that clinicians might need to be aware of?

Dr Cash:

Well, in my experience, what I've seen is patients coming in... this is more in the lines of not necessarily having the lower GI symptoms with the diarrhea, but sensitivities to a class of foods that falls into an acronym called FODMAPs. And that stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. And I tend to think of these as poorly-digested fibers and sugars.

Now, patients often can have IBS-like symptoms when they ingest FODMAP-containing foods. It's a major part or class of constituents of our typical American diet. And they often will have bloating and perhaps some looser, more urgent stools, abdominal pain. Again, no specific test for those. It's really an elimination process and then a gradual reintroduction of certain foods. But those would be the most classic and the most common things that we see in clinical practice now. We also will see a lot of patients who will come in with upper GI symptoms such as reflux or GERD. And they'll identify foods and other dietary constituents such as caffeine or sodas or chocolate or spicy foods.

And they'll have upper GI symptoms, perhaps what we call dyspepsia, which is pain in the upper part of the abdomen, the epigastric area. They may have reflux symptoms. And those also are common intolerances or sensitivities. And finally there is another condition that's kind of a quasi- food allergy, and that's called eosinophilic esophagitis. And these patients will come in with a symptom of dysphagia, or difficulty swallowing. Food feels like it's getting stuck, and sometimes it actually can get stuck. And that is an immune-mediated response to certain types of foods, the same ones that I mentioned, the big 5 or 6 that we alluded to.

And this is a condition where a specific type of immune cell called an eosinophil actually infiltrates the lining of the esophagus and causes some fibrosis and some thickening, and the motility of the esophagus is affected. And food can literally get stuck. And that's a condition that needs to be treated with both food elimination of those types of foods, but we also treat it with topical steroids. And those would be the most common things that we see in clinical practice.

Dr Lacy:

Wonderful, Brooks. Thank you very much. So you've kind of already alluded to this, but I just want to pin you down a little bit because this is a question that comes up all the time about a validated, verified test to make the diagnosis of a food sensitivity. I have patients who come in showing reports from hair samples, fingernail samples, stool samples. Are these good tests? Are they accurate? Do we have a validated test?

Dr Cash:

No, we really don't. And we don't believe that they're accurate. And I would encourage our audience not to pursue that testing because it can be very misleading. There's probably about 11 or 12 different tests that people do. And there's terms such as facial thermography and gastric juice analysis. You alluded to a couple, the hair analysis. There's assays that look at what's called cytotoxicity. None of these are recommended as tests that are thought to be accurate or predictive for immune-mediated food allergies. So we recommend that people don't avail themselves of these tests because we really just don't know what they mean.

Dr Lacy:

Wonderful. Thank you. I would be remiss, since we've got you on the line here, if I did not ask your opinion on alpha-gal syndrome. How common is this? Is this a new disorder or did we just overlook it in the past? And what's the mechanism?

Dr Cash:

Yeah, that's a great question and I'm glad you mentioned it. Alpha-gal, it's not a new disorder. It's actually a tick, or it's a tick-borne acquired allergy to red meats. Typically beef is the classic one. This is a condition that's caused by a bite of what's called the lone star tick, and it's given that name because of a marking on its thorax. I'm probably not being very accurate there in terms of my description of a tick, but this is a condition where people can develop a true IgE immune-mediated, that's an immunoglobulin type E immune-mediated allergic reaction to red meats.

And they will have those classic symptoms that we mentioned. The rash or the urticaria, perhaps even anaphylaxis, abdominal symptoms, abdominal... so pain and diarrhea. We don't know how common this is. There are regional distributions to this, of course, because it's going to occur where the tick lives. But it is something that's gotten more and more focused over the last several years and it's something that we will occasionally test for when we get patients who come in with these types of symptoms.

Of course a really good history is important to try and tease this out and identify this. There is a test for it, and so it can be identified. And then the treatment is removal of those types of foods from the diet. So very up and coming, a hot topic. I wish I could tell you just how common it is. In my experience, it's rare. But I think that there's also a lot of misdiagnoses because a lot of people are not aware of this. It doesn't come to front of mind when we're talking to patients. But if you do get that classic food allergy history, I do think it's worth testing for to see if it's there, because we need to get better information about how common this might be.

Dr Lacy:

Yeah. And as you mentioned, Brooks, there is a geographic variation. A little bit more common in the south, where the lone star tick is more common. And you also mentioned earlier on, maybe keeping a diary. So some patients keeping a food diary. Then they can see a reproducible pattern.

So Brooks, as we wind down here, when should a patient be referred to an allergist to evaluate food-related symptoms? Should all patients with food-related symptoms see an allergist at some point, or just those you really suspect as having a true food allergy?

Dr Cash:

Yeah, I think it's the latter. I think most people who come in with food sensitivities and self-identified food intolerances can be managed by their primary care provider or a gastroenterologist in conjunction with a nutritionist who's well-versed in these conditions, or a dietician. The referral to allergy immunology I really reserve for those patients who have the systemic signs of food allergies. So if they have the urticaria, if they have the upper airway symptoms, if they have angioedema, or swelling of the lips or mucus membranes, those are the patients that I will send for formal allergy testing with that single blind food challenge type testing. And that's really, I think, the small sliver of patients that need to be referred for allergy testing. It's those additional, more systemic symptoms that fit into that classic paradigm that we see.

Dr Lacy:

Wonderful. Brooks, again, and not surprisingly, this has been a wonderful conversation. You've educated me, you've educated our listeners. Any last thoughts for our listeners?

Dr Cash:

Well, I just want to thank you again for the time and the platform to talk about this important topic. I do encourage our listeners to educate themselves about food allergies and sensitivities. If they have questions about this, I would encourage them to talk to their primary care provider. There's a wealth of information out there. There's also a wealth of misinformation that's out there. So assess the data very carefully. Recognize that food allergies are quite rare. But if people are having symptoms that are extraintestinal or extragastrointestinal, I do think... and they identify that with certain food intakes, especially those classic 5 or 6 foods that we talked about, I think it's important that they do mention that to their providers. And they may need some additional testing. But these are rare conditions, but they can also be very serious conditions if they're identified.

The other good news that I want to throw out there is that many food sensitivities or specifically food allergies can attenuate over time. So it's important for people to realize that even if they have a food allergy or a child with a food allergy, that there's a really pretty good chance, 40%, 50% that that food allergy may actually dissipate over time as the child ages. And so that's something else to recognize, and to give some hope and some solace with regards to these conditions as well.

Dr Lacy:

Wonderful. Thank you so much. To our listeners, you've just heard another great edition of Gut Check, a podcast from the Gastroenterology Learning Network. My name is Brian Lacy. I'm at the Mayo Clinic in Jacksonville, Florida. And we've just heard this exceptional review on food allergies and food sensitivities from Dr Brooks Cash, professor of medicine and chief of gastroenterology, hepatology, and nutrition at the University of Texas Health Science Center in Houston, Texas. Again, to our listeners, thank you for joining in. We look forward to having you join us for another podcast. And once again, thank you to Dr Brooks Cash for his expertise and educational insight today. Best wishes to all.