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Why Do Some People Suddenly Develop Food Allergies Later in Life?
It can be confusing and daunting to suddenly not be able to eat a food you've eaten your whole life.
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In 2013, my digestive life went to crap, nearly literally. I started to have strange episodes where my stomach would feel like it was crushing in on itself, leaving me bent over in the bathroom for hours. Then, I would randomly break out in hives on my arms, or around my mouth. Other times my throat felt extremely tight, never enough to cause breathing problems, but enough to freak me out. I sought out a doctor to tell me what was going on.
She put me on an elimination diet, when you stop eating the top eight food allergens, and made an appointment for me to get tested for a food allergy. I had never been allergic to anything before (though I am lactose intolerant), so I was skeptical that a food was the culprit.
But a few weeks later, she gave me the news: Congratulations, I was allergic to soy. (I’ve since confirmed this again and again through accidental and painful exposures to it.)
I ate soy throughout my whole childhood. My mother is Chinese and did the bulk of the cooking: soy sauce, tofu, edamame, tempeh—we regularly indulged in the soy smorgasbord. How could I suddenly have become allergic?
My doctor’s answer: “I don’t know.”
Food allergies are a mysterious affliction, and perhaps the one thing we know for sure about them is that they are increasing—as much as 20 percent in the past decade. A study that came out in the first week of 2019 in T he Journal of the American Medical Association (JAMA) reported that in a survey of 40,443 US adults, an estimated 10.8 percent of them had a food allergy, and nearly half of those people had at least one food allergy that had cropped up in adulthood. A quarter of them, like me, had never had a food allergy as a child.
“That was pretty surprising to me,” says first author Ruchi Gupta, a professor of pediatrics and medicine at Lurie Children's Hospital in Northwestern Medicine. “You can extrapolate that to say that at least half of adults carry their food allergy into adulthood. And then there's this additional [group] that are developing newer food allergies as adults.”
Gupta confirms it’s a confusing situation for patients. We wonder to ourselves, what happened to our bodies? What has changed?
Cathryn Nagler, a scientist and professor at the University of Chicago, says that the speed at which food allergies have been increasing rules out certain causes. “Our hypothesis is the increase in prevalence can't be genetic,” she tells me. “Genetics don't change that quickly. It must be due to the environment.”
She tells me that she, and others, think the rise in allergies is explained by environmental factors changing our microbiome, the bacteria that live in our bodies.
The two biggest offenders? “Misuse of antibiotics and the loss of dietary fiber from our diets,” Nagler says. “Even if you personally shun antibiotics, they're fairly stable as drugs, and they're present in more foods and in our water supply than you'd like to know. The loss of dietary fiber from the diet has been observed pretty consistently. Americans are famously enamored with fast food, or processed food that all of which are low in fiber.”
Certain bacteria feed off of fiber, and by lowering the amount of it in our diets, we could also be altering our bacteria populations—starving some bugs and encouraging the growth of others. Similarly, antibiotics might be changing the types and amounts of bacteria that make up our microbiome by killing some and favoring others.
In another recent study, out in Nature last week, Nagler and her colleagues took one step towards uncovering how exactly the microbiome could be linked to food allergies. They found that when gut bacteria from healthy human babies were put into germ-free mice, those mice were protected from an allergic reaction to cow’s milk. But if the mice got bacteria from babies who were allergic to milk, the mice had an allergic reaction to milk, and not a mild one. The mice experienced anaphylaxis when they were given cow’s milk for the first time.
“We can show very, very clearly that the mice that got the microbiota from the healthy infants were completely protected from an allergic response,” Nagler says.
The researchers looked at which microbes were present in both the healthy and allergic mice, and found that one particular bacteria species, called Anaerostipes caccae, seemed to be helping protect the mice from the allergic reaction when it was present.
When they compared differences in the mice’s gene expression, or which genes were more or less active, they saw differences in the intestinal epithelium, which is the thin lining of the small and large intestine. The next steps are to uncover exactly what Anaerostipes caccae is doing to change this lining, and how exactly that change alters the immune response.
The new findings line up with her and her collaborators’ other work: In 2014, Nagler and others found that a class of bacteria called Clostridia could help protect against nut allergies. (Intriguing, Anaerostipes caccae is part of theClostridia class.) This class of bacteria produces a compound called butyrate, which is an important nutrient for a healthy microbiome, she tells me.
In 2015, Nagler and her collaborator Roberto Berni Canani at the University Federico II of Naples in Italy found there were big differences in the gut bacteria of babies with and without cow’s milk allergies. Children who became tolerant to cow’s milk through dietary management had higher levels of butyrate in their feces, emphasizing that butyrate might play an important role in allergy protection.