TL;DR: Less sensitive celiacs can probably have trace amounts of gluten cross contamination with low risk of health problems, since celiacs who deliberately eat non-trivial amounts of gluten are mostly ok.

Celiac disease is an autoimmune condition where your immune system becomes triggered by gluten. This leads to a variety of strange effects on your body. Gastrointestinal distress symptoms (diarrhea, flatulence, irritable bowels) are the most obviously connected, but a large proportion (my guess is 30-50%^[1]) of celiac sufferers don't get these. Other common symptoms are weight loss, iron deficiency, weak bones (density loss), psoriasis (itchy skin patches) and damage to your small intestine (villous atrophy). 1-2% of people globally have celiac, though most are not diagnosed.

The universal treatment ordered is a strict gluten free diet. This makes sense, and for me personally was relatively easy to do given the range of options these days.

The killer is that to do it strictly you must avoid cross contamination at all costs. While cooking this is not too hard as long as you use separate utensils. But it means you practically cannot eat out, since you don't control the preparation.

It's difficult to classify restaurants as 'safe' or not, which severely restricts your ability to eat out. Many restaurants that are actually very careful will still tell you they can't guarantee it's gluten free. How do you know whether they are saying that because they throw spaghetti at each other, or if they just understand how hard it is to clean all contamination traces and don't want to be sued?

On the other hand, many restaurants insist they are safe, but do not know the implications of catering for celiacs. So they fry the fries in oil that has fried glutenful things, which transfers a surprising amount of gluten.

The personal cost of this is high. Eating out is important for convenience options and for social inclusion. One paper notes that "GFD is very restrictive, resulting as a burden on social life and quality of life". More plainly: it sucks. I did it for two months but the cost was too high to accept as a rule without question - I wanted more evidence to weigh up the benefits.

But the blanket rule of "celiacs strictly avoid gluten" was black and white. There was no preformulated risk model for me to plug my parameters in - information on gluten thresholds and health impacts was not easy to come by. My gastroenterologist admitted that dose sensitivity is a thing, but said that there is still a lot of uncertainty in the science and my best move was to do the strict thing, otherwise I will have significantly higher risk of cancer (small bowel lymphoma) in 30 years. My local Facebook group was largely unimpressed with my research, with the most liked comment insisting "Coeliac is coeliac, it doesn’t vary in degrees. ... We follow Coeliac Australia’s advice which is formulated by a medical board of experts in the field. That is to avoid all gluten including cross contamination."

Given the blanket rule and threat of unlikely but extreme outcomes, how does the celiac population fare with diet adherence? Not great - up to 50% don't manage to do it strictly. I ran a poll in the aforementioned group and 39% of celiacs said they "sometimes knowingly eat things with traces (or restaurants eg shared fryers)" (n=298).

The reason I'm writing this post is that the advice to strictly avoid cross contamination, while well meaning, in my not-medical-professional-this-is-not-medical-advice-talk-to-your-doctor opinion, is on the wrong side of the cost benefit tradeoff for many people, and I want to improve the quality of life for other celiacs.

The good news for most celiacs is that sensitivity to gluten does actually vary widely (sorry Michelle). If you get severe reactions to tiny amounts of gluten (like the shared fryer), this sucks and you have my sympathy. But if you are on the mild side (or maybe even moderate), you can almost certainly have fries and not worry about raising your risk of cancer from miniscule to small.

Research which evaluated celiacs for diet adherence found that out of the 8% (109) who were deliberately eating gluten (on average the equivalent of 5g of flour per day), only 23% had gluten enzyme antibodies (the main marker for celiac) and 33% had villous atrophy (small intestine damage). However a further 9% had small intestine inflammation (interestingly, this group also ate the most gluten, on average equivalent to 13g of flour per day).

I don't recommend that people with celiac start inhaling small amounts of flour daily. There's a strong selection effect on this group - if you're deliberately eating gluten I bet your immediate symptoms aren't as bad and therefore you probably have milder celiac (although 25% of the gluten eating group did report gastrointestinal symptoms). Someone with severe sensitivity can't start eating gluten and get results as good as the 8% gluten eater group. The other caveat is this is just one paper, and while the size of the group wasn't small (109) it wasn't that big either.

Given people with (probably milder) celiac can have non-trivial amounts of gluten and be mostly fine, it's reasonable to believe that if you're a milder celiac, you can have tiny amounts of gluten from cross contamination with low risk.

How would you know if you're a mild celiac? I'm not well calibrated here. A good indicator is likely blood testing (usually tTg-IgA). How high were your initial results when you were diagnosed? The level of small intestine damage is probably key - if you only had inflammation (no atrophy) that could suggest you're mild. But also not having obvious gastro symptoms (or only minor ones) in response to eating gluten is a good bet to indicate milder celiac. According to my second gastroenterologist (who pointed me to this research), I'm likely mild because my tTg-IgA was only 50, my small intestine had minor inflammation and my iron levels are fine (though my bones are weak).

For me, the tradeoff I'm now taking between my health and quality of life is to not eat things with gluten ingredients, but not worry about cross contamination. I'm getting regular blood tests to watch my tTg-IgA, and if it starts rising then I will need to re-evaluate. But so far it has continued to go down. Your mileage will vary, the human body comes with a stupendous amount of variables so your situation won't be the same as mine - but I hope this post gives you the information to make good decisions.

This is a hard figure to come by, because asymptomatic people are often undiagnosed, and after diagnosis some people realise they had symptoms they thought were just normal, which itself might be hindsight bias. This article notes 28% of undiagnosed celiacs had no symptoms but does not provide a real citation, and this paper found 48% of female celiac patients did not have prominent gastro symptoms ↩︎