Whether you're a gluten-free-bagel fan or you think it's all just a fad, gluten sensitivity (without celiac disease) is still controversial. However, a recent small study may help clear up some of that confusion: Researchers have identified the way one protein may change the way our guts react to certain foods, reports NPR. For the study, presented in October at the annual United European Gastroenterology Week, researchers measured 72 participants' levels of a protein called zonulin. Of those participants, 27 had non-celiac gluten sensitivity, 15 had celiac disease, 15 had irritable bowel syndrome (IBS), and another 15 were healthy volunteers. The researchers found that those with celiac had the highest levels of zonulin in their blood, followed closely by participants with non-celiac gluten sensitivity, those with IBS, and then the control participants. Zonulin helps keep your gut from getting too "leaky" by controlling the size of the gaps between the cells in your intestines. This, in turn, influences how quickly things pass through your guts. Other research has linked zonulin to both Type 1 diabetes and celiac disease. The idea is that, if you eat certain foods and you've got higher-than-normal levels of zonulin in your system, those gaps in your cells will stay open longer than they're supposed to. Thus, your gut may "leak" substances into your bloodstream and cause damage. Still, it's unclear from this small study how having more zonulin in your system might change your individual digestion patterns. And there are still a lot of unanswered questions about both "leaky gut syndrome" and non-celiac gluten sensitivity, which may or may not actually have anything to do with gluten. So, while zonulin may help explain a lot, there's still plenty more explaining to do.