Professor of Gastroenterology at Michigan Medicine, Dr. William Chey talks about finding food triggers in IBS patients.
Interview conducted by Ivanhoe Broadcast News in 2023.
What does IgG stand for?
Chey: Immunoglobulin G, it’s a certain type of antibody. And these antibodies are directed against certain food constituents.
Without this test, how would you test somebody with IBS? What would the standard way be?
Chey: Typically, the way we diagnose IBS is by utilizing symptom-based criteria. And the characteristic symptoms of IBS include abdominal pain and altered bowel habits. So problems with diarrhea or constipation or in some people both. And we also do a limited number of diagnostic tests to exclude other conditions that can mimic IBS. So things like celiac disease, inflammatory bowel disease, in persons over the age of 45, we always make sure that we do colorectal cancer screening. So for the most part we do symptom-based criteria and a few tests to exclude other organic diseases that can present with the same symptoms of IBS.
Once you’ve excluded and you know that it’s IBS, the classic way you talked about elimination diets and stuff like that. What did that consist of or does that consist of and how long does that take before it’s all figured out?
Chey: Well, here’s the thing is that I think it’s always important to establish whether a patient with IBS has symptoms are related to eating a meal or not. Now it turns out that probably more than three-quarters of IBS patients associate either triggering their symptoms or their symptoms getting worse with eating a meal. So food is probably the singular most important trigger for IBS symptoms. That said, right now I think increasingly doctors are coming to this recognition. They’re asking about the association with food and they’re typically utilizing a diet called the low FODMAP diet. FODMAP is an acronym that stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols, which is a mouthful. But basically it’s just an abbreviation for short chain sugars that the humans small intestine either has difficulty or can’t break down and absorb. And because of that, these sugars get down to the colon where they’re fermented by the bacteria that live there producing gases and chemicals that can trigger IBS symptoms. Now, the good news is that diet makes around 50-60% of patients better. The bad news is that 40-50% of patients don’t get better. And it’s also an empiric strategy. So meaning that we determine whether somebody has IBS, determine whether or not their symptoms are related to food. And then think about trying the low FODMAP diet. So it’s a pretty blunt instrument. And so thinking about strategies that pursue more of a precision medicine strategy, I think are really attractive. And this new form of IgG based food sensitivity testing might provide that take on approaching patients with IBS.
How does it work?
Chey: Basically, the patient gets a blood sample drawn and the blood sample is tested for various antibodies to common food triggers and patients with IBS.
So, it’s as simple as just go into a lab like you would get any other blood tests, basically?
Chey: Yeah. And then basically based upon the results of the test. An elimination diet is fashioned based upon the IgG antibody profile to the various common food triggers for IBS.
Instead of going full-on low FODMAP and taking everything out, and I presume you gradually introduce things back in, is that how it would work?
Chey: With FODMAP, yeah.
So, now you can look at the blood test results and what does it tell you?
Chey: It’s telling you whether or not there are proteins in the food that your body is- your immune system is reacting to and forming antibodies to. And so eliminating those foods in our study was associated with an improvement in overall IBS symptoms.
How long is the elimination diet after the blood tests versus what it had been or how short, I should say? Because you’re able to much more quickly determine what you should get rid of?
Chey: I’m not sure that really influences how quickly or how slowly people respond, but usually people will respond within a period of two to four weeks.
Once the blood test results are in you- so a typical patient, we’re going to interview someone afterwards. You see the blood work and you say like, don’t eat this, this and this is, is it as could you try to simplify that?
Chey: No, not really. That’s basically it. And this strategy has been utilized by other investigators before the results, with previous studies have been quite mixed. And I think one really important thing to realize about this test is the rigorous methodology that was utilized to select the foods that are included in the test. So all IgG based elimination diet tests are not the same.
So, when you said the foods that are selected to be used in this test, can you expand on that a little bit more?
Chey: Maybe a little bit. Basically, the way the foods were selected was from a very large panel of different foods that are commonly ingested in the western diet. Looking at antibody levels broadly across patients with IBS versus healthy controls, and a smaller number of foods, 18 actually were selected- met the final selection criteria for inclusion in the test. And this methodology that was used to select these different foods is more rigorous and also more evidence-based. The IEEE based upon data from patients and controls than probably any previous IgG based food sensitivity test.
The blood test results are what led you to the 18 foods. What are the 18 foods?
Chey: I couldn’t tell you.
Is there a typical food that you find or does it vary from patient to patient?
Chey: It will just stay with that. I’ll restate that for you in a way that’s a little more clear. This test, not unlike other strategies, diet-based strategies, have focused on foods that contain gluten or a carbohydrate called fructan which is commonly contained in wheat. In fact, wheat shakes out as an important part of this test as well as the low FODMAP strategy and a gluten-free diet, of course.
Most people with IBS, do they recommend gluten-free?
Chey: No. But right now, a gluten-free diet again is an empiric diet. So like low FODMAP, you would just make your best guess and eliminate foods that contain gluten. And then gluten is also a bit misunderstood because people think that when they eliminate wheat if their symptoms get better, it’s because they’ve eliminated gluten. That’s true for some individuals, but actually, research shows that a larger proportion of people that eliminate wheat from their diet get benefit from eliminating the carbohydrate or sugar in wheat, called fructans. Fructans are a type of short-chain sugar that universally cannot be broken down or absorbed in the human small intestine, and for that reason, get to the colon and are fermented to produce gases and chemicals. Fructans are an important part of the low FODMAP strategy.
Is there anything else you think is important?
Chey: As far as the study goes, the way patients who were selected were utilizing the Rome criteria and selected diagnostic tests to confirm the diagnosis of IBS. Then they underwent the testing, and if a small percentage of patients actually don’t react to any of the foods that are contained in the test, then those patients were eliminated. The patients they did have abnormal levels of IgG antibodies to various foods, were randomized then to receive either a true elimination diet-based upon the test results, or a sham elimination diet, which was not based on the test results.
And so then obviously the ones who didn’t get the sham diet performed significantly better.
Chey: They did. What’s interesting though is that of course the patients were blinded, they didn’t know which diet they were on. These kinds of things are always tricky to deal with diet studies. But I think that we were able to do this quite successfully as part of this trial. As far as the main results go, when you looked at overall symptom response and also in particular, benefits to abdominal pain, for the overall population, there was a trend towards benefit with the IgG-based elimination diet. But it was not statistically significant. On the other hand, when you looked at individuals with IBS and constipation and IBS with a mixed bowel pattern, there were significant benefits for abdominal pain. If you looked at overall symptoms, actually all the groups benefited.
When I said what else is important about it, what did you want to add that you think is important?
Chey: So we talked about the importance of the role of food in managing patients with IBS. I think an important thing to realize is where we are right now in that discussion, which is a great deal farther than we were 10, 15 years ago. When I started this whole journey as a gastroenterologist in 1990, I was actually told at that time that there were no diet therapies that were beneficial for patients with IBS. So the fact that we have a number of strategies that are beneficial for IBS is an incredible advance. On the other hand, it is important to recognize that right now we’re just pretty much guessing. Really, which diet you get for IBS highly depends upon which diets the doctor taking care of you is familiar with. Right now, by far and away the most commonly utilized one is low FODMAP diet. But depending on who you see, you might get a variety of other types of diets, which may or may not be evidence-based. And in fact, a lot of the commercially available diets like IgG-based diets, leukocyte activation testing, mediator release testing, all of these are commercially available diets are to varying degrees evidence-based. I think one thing that’s really exciting about the study that we’re talking about is that it’s a rigorous, very large study that provides compelling evidence that IgG-based food testing might offer benefits for some patients with IBS.
So, for somebody seeing this or hearing this, and you’re talking about the state of the disease right now, and they want this evidence-based testing, what do they do? Do they ask their doctor for this blood test? How does it work for the “average Joe”?
Chey: I believe it’s commercially available. I don’t know the commercial side of this at all.
END OF INTERVIEW
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