IgG Tests for Irritable Bowel Syndrome (IBS): A Research Summary and Analysis

In this NatNotes blog post, we’re going to be looking at the best trial on IgG testing for irritable bowel syndrome (IBS). Recently, I have been pouring through all of the studies and there aren’t that many, but all of the studies on food sensitivity testing for the treatment of irritable bowel syndrome, and this is the very best of them, the cream of the crop. It is what a food sensitivity testing research looks like at its very best. So I thought I’d walk you through this good trial.

This is a little bit of an oldie at this point. It came out in 2004, but it is a goodie. It was done in Manchester, England by a group of researchers and published in the BMJ. So, of course, an excellent medical journal.

So we’ll start with some background on Irritable Bowel Syndrome (IBS). Irritable bowel syndrome, of course, is horrendously common affecting somewhere around 10% of the U.S. population and while being so common, treatments for it are lackluster. There are a lot of people who are not experiencing adequate relief and are looking for other ways outside of conventional medicine to find a good, durable, relief. So they oftentimes come to integrative practitioners looking for another way.

There are multiple theories on what causes IBS from hyperalgesia, saying that it’s basically fibromyalgia of the gut; to small intestinal bacterial overgrowth (SIBO); to colonic dysbiosis. But another theory that it lives in the integrative medicine camp is that maybe it’s caused by or at least exacerbated by immunological reactions to certain specific foods. These are most commonly thought to be IgG reactions, and they’re determined based on either an elimination diet or most commonly IgG. So your logic testing of for IgG food sensitivities. While I say most commonly, we don’t actually have great data saying that this is what people use to determine food sensitivities, but it’s most common among the practitioners that I know and the practitioners that I have practiced with. If you look in most textbooks of natural medicine, that’s what you would find.

Here we’ll explore the study’s vitals. This study was a randomized double-blind controlled trial, and it was looking at 150 adults with IBS, so determined by the Rome II criteria and the type of IBS was not specified. It was a really basic study design. It was a two-arm study design with an intervention arm that had an elimination diet that was guided by IgG testing and then a control arm that had an elimination diet that was determined at random. So different participants eliminated different random foods. The primary outcomes were, the IBS symptoms severity score, and a global IBS rating after 12 weeks. The most commonly eliminated foods on the true elimination diet where yeast, milk, wheat, eggs, cashews, and beef, and if you’ve run a number of IgG food sensitivity panels, you’ll know that these are commonly eliminated foods. These foods are commonly detected foods as having, IgG reactions too. So, a not surprising list if you’ve been running IgG testing.

A quick look under the hood of this study will show that it’s a good quality study and that it meets most of my criteria for what I’d consider a well-designed study. If we shift over to the risk of bias analysis as well, we’ll see that it is a low risk of bias study, other than that there’s this area called reporting bias, where we look to see, did they report on all the outcomes that they measured and also did they measure just too many outcomes.

So moving onto the results. First, the IBS symptom severity score, this is a scale that’s out of 500 points. Both groups covered around 300 to start, but we saw that there’s a 10% greater drop in IBS symptoms severity scores in the true elimination diet arm versus the sham elimination diet arm, whereas the scores dropped by 30% for the true diet and 20% for the sham diet. So we do see more improvement occurring with the true elimination diet. These, of course, are an average of the scores. So there might be some people who got a whole bunch of improvement and some people got very little improvement and we’ll see that more as we shift over now to the global rating.

With the global rating, we have, first, an intention to treat analysis where we see that yes, a greater number of people with the true elimination diet experienced improvement compared to the control group. We have, 18 participants which are 28% of those in the true elimination diet, experiencing improvement; and 16% of those in the sham elimination diet experiencing improvement. So that is a number needed to treat of 9. Meaning for the true elimination diet, or IgG testing guided elimination diet, that 1 in 9 people will experience benefit just because of the special diet.

If we shift over to the full adherence analysis or what’s more commonly called a per-protocol analysis, we see that when we look at just people who were adherent to the Diet, 54% of people in the true elimination diet, that arm saw improvement versus only 15% and the sham elimination diet. So with the sham elimination diet, there’s no additional improvement based on adherence. But with the true elimination diet, we see a significant jump, almost a doubling of improvement based on its adherence. One thing to note here is that we see a whole bunch more people were adherent in the sham arm versus the true elimination diet arm, which makes me wonder, was the sham diet a lot easier to follow? I don’t know the answer to that. They didn’t have any clues in the text why that was. But over all, there’s a number needed to treat for the per-protocol analysis of 2.5.

There was a phase that I didn’t tell you about, this is the challenge phase, where they invited all of the participants to reintroduce eliminated foods. 93 people took them up on this adventure, and after reintroducing foods, they gave them the questionnaire four weeks later to see did they get worse–which is what we would expect if you reintroduce foods that you’re sensitive to, your symptoms should get worse. What we see is, yes, 41% of the people on the true elimination diet that got worse compared to 25% percent of people on the sham elimination diet. So there was a worsening of symptoms in the group that had the true IgG guided elimination diet.

So in conclusion, this is a well-designed study and to me, it’s surprising that it hasn’t been repeated. I hope they do repeat it because it shows that this might be an avenue of relief for a number of people with IBS symptoms. The IgG testing guided diet not only improved symptoms when they removed food sensitivities from their diet, but it also their symptoms worsened more substantially once the foods were reintroduced. This to me shows that, yeah, there seems to be some more signal rather than noise going on here.

This study suggests that food sensitivity testing will be beneficial for at least 1 in 9 patients, and this number or ratio likely decreases or, in other words, improves if your patients are adherent to the diet. It may help decrease the symptoms by an average of 30%, and for certain individuals, it’s going to be much greater than 30%.

A long-term study would be really nice on the subject. This could show us how durable this improvement is. Is this something that only works for a few months? It would also help decrease the noise of the placebo effect, and so we could really see, what’s the difference between the true elimination diet versus, a randomized diet. This would help get some of the noise of the placebo effect out of that equation because the placebo effect decreases over time.

So, the final question I always ask myself with any intervention is, is it ready for prime time. For this particular intervention, I think that the question is a little bit funny because it’s already being used. People are using it as if it’s in prime time, which makes sense. It’s a low risk of harm intervention if you’re using it judiciously. But it’s being used and this helps provide some context for that use, and shows that it does look like it could be efficacious for people. It’s usually an out of pocket expense for patients, so this just helps give some data to the out of pocket expense. We have data that shows that this might be worthwhile.

So I hope this trial helps you give good informed consent to your patients about the potential benefits, for IgG testing for IBS and also helps you clearly say that, while we think that there are some benefits from a research perspective, those are not definitive yet. So I think, yeah, it can be ready for prime time. People can use it. I don’t think that there’s a risk that they’re going to be hurting their patients, but I don’t think that you’re going to convince a very skeptical practitioner with this study alone.

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