Celiac disease is an autoimmune condition where the immune system reacts against a modified version of a gluten protein that results in a cross-reaction with the small intestine because of similarities in protein sequence. Individuals with this condition can get chronic inflammation, cancer and malabsorption of important nutrients if they do not eliminate gluten from their diet, so this is a very real condition. However, it has spawned a dietary fad and many people who do not have celiac disease have self-diagnosed themselves with “non-celiac gluten sensitivity” (NCGS) and avoid gluten like the plague in a misguided quest for healthy eating. There is no scientific evidence that NCGS exists, but that has not put a dent in the popularity of gluten-free products.
Grounded Parents is a blog about parenting written by parents who are secular skeptics and it is part of the Skepchick Network. Recently, they published a post written by Jenny Splitter defending decisions to eliminate gluten for those who claim to have NCGS. Now, Splitter did not argue that there is scientific evidence for this condition. Instead, she appealed to placebo medicine, ignored the negative consequences of overfitting noise, deployed a classic anti-skeptical trope based on the perfect solution fallacy and even rationalized negative evidence.
Splitter starts of my making two scientifically valid remarks: (1) there is no evidence for the existence of a special sensitivity to gluten apart from celiac disease, (2) gluten-free does not necessarily mean healthy. However, she then deploys the following remarkable argument:
If you stop eating gluten, and physical symptoms improve, have you proven some significant scientific correlation? Of course not. But let’s be realistic. If you’re suffering from something for which doctors have given you no cure, and you find something that seems to work, why wouldn’t you just stick with it? At some point it becomes obnoxious to demand to see the scientific evidence behind every lifestyle choice an individual makes. None of us live in some sort of perfect evidence-based world. Sometimes we all wing it.
There are numerous problems with this paragraph.
Why not just stick with it?
Chronic conditions involve relapsing and remitting events, which means that the condition fluctuates from day-to-day and week to week. Thus, there is considerable background noise that interferes with any causal inference from diet to alterations in symptoms. It is often the case that people think that something thinks causes an improvement or deterioration when it just happens to correlate with the natural ups and downs of the condition (regression to the mean). So chances are, when you have “found something that seems to work” you are just overfitting the random noise of your condition (especially when confirmation bias comes into play and you remember the hits and forgets the misses). In other words, the error rate of this method is probably substantial. This means that it is unlikely to be productive for long and instead lead to excessive anxiety about diet, elimination of unharmful food items (or perhaps even important, healthy items as well), an overconfidence in personal ability to distinguish harmful dietary items from harmless, an overreliance on placebo effects and the illusion of control. A “mistake” (i.e. diet alterations that do not improve symptoms above and beyond placebo or caving and eating one of those eliminated food items) can be interpreted as personal failure to manage a supposedly diet-manageable condition instead of random noise and so could lead to additional self-blame. Thus, sticking with something just because it “seems to work” is not always rational (since the error rate is substantial) and not without negative consequences.
There is one objection that will surely be deployed and that is the “adults should be able to do whatever they want”. However, this is not about what adults should or should not be able to do. Rather, it is about what is reasonable and what is not.
The perfect solution fallacy as an anti-skeptical trope
Another major issue with the paragraph quoted above is that it makes use of a classic anti-skeptical trope: the misinterpretation of scientific skepticism as an obnoxious and intrusive demand for evidence in all aspects of life. In reality, scientific skepticism on a personal level is about not fooling yourself. The trope erects a perfect solution (“demanding evidence behind every lifestyle choice”) and then dismisses the more realistic approach of critical self-examination because it fails to fulfill this imaginary ideal that no one actually holds. Thus, it is a combination of a straw man fallacy and a perfect solution fallacy. The fact that it is not really practically possible to “demand evidence for every lifestyle choice” does not mean that she should refuse to have a skeptical approach in the context of the gluten-free fad.
To drive the point home, let us look at this paragraph again. However, this time we will replace “stop eating gluten” with your favorite alternative “treatment”, such as acupuncture, homeopathy, herbs or reflexology:
If you [start reflexology/acupuncture/homeopathy], and physical symptoms improve, have you proven some significant scientific correlation? Of course not. But let’s be realistic. If you’re suffering from something for which doctors have given you no cure, and you find something that seems to work, why wouldn’t you just stick with it? At some point it becomes obnoxious to demand to see the scientific evidence behind every lifestyle choice an individual makes. None of us live in some sort of perfect evidence-based world. Sometimes we all wing it.
No reasonable person would ever accept this kind of argument for reflexology. Thus, we should not accept this argument for the gluten-free fad.
Rationalizing negative results
It gets even worse in the next paragraph, where Splitter makes use of classic alternative medicine rationalizations of negative study results:
Plus, let’s remember what the gluten sensitivity study actually showed. While it looks like there’s no support for most claims of gluten sensitivity, that doesn’t mean that the symptoms weren’t real in many cases or that gluten was found to be harmless for every condition other than celiac disease. In other words, as always, more research is needed.
A reflexology proponent would rationalize negative results by arguing that although “it looks like there’s no support for most claims of [reflexology], that doesn’t mean that the symptom [relief] weren’t real in many cases or that [reflexology] was found to be [ineffective] for every condition […]. In other words, as always, more research is needed.” Yes, there are many additional complex complications with the gluten situation that is not true for e. g. reflexology. However, no reasonable person would ever accept this kind of special pleading for reflexology. Thus, we should not accept it for gluten-free fad. Yes, we should not automatically dismiss someone without celiac disease who eat a gluten free diet, but we should not so casually stoop to classic alternative medicine / anti-skeptical tropes.