The Nuance

How the Western Diet Is Wreaking Havoc on Our Guts

Experts say a range of factors — including how we eat — may explain the rise of IBD and other gut disorders

Illustration by Kieran Blakey for Elemental

Gut health in America is poor and seems to be getting worse. According to a 2020 study led by researchers at the University of North Carolina, roughly one in four U.S. adults regularly experiences diarrhea, constipation, stomach pain, or other symptoms of gastrointestinal dysfunction.

Meanwhile, about the same proportion of Americans — one in four— has gastroesophageal reflux disease (GERD), a condition in which the stomach’s contents migrate up into the throat and food pipe, causing heartburn and other symptoms. GERD used to be relatively rare among people under the age of 50, but a 2018 report from Case Western Reserve University in Ohio found that between 2006 and 2016, the prevalence of GERD rose steadily among younger adults — especially those in their thirties.

Some experts have speculated that these and other discouraging trends in disease prevalence may be partly attributable to “diagnosis creep,” or the steady expansion of diagnostic criteria so that an ever-broader group of people qualify as sick. (A problem that a physician may have once shrugged off as “the runs” or “a little heartburn” may now garner a diagnosis of irritable bowel syndrome or GERD, respectively.)

But no one is downplaying the decades-long rise in inflammatory bowel disease (IBD), a group of conditions — primarily Crohn’s disease and ulcerative colitis — that are associated with immune system hyperactivity. This hyperactivity produces flares of inflammation, and the attendant symptoms include wrenching pain, diarrhea, fatigue, rectal bleeding, and GI damage.

“Following World War II, we’ve seen a rapid rise in IBD incidence throughout the developed world,” says Gilaad Kaplan, MD, a professor and gastroenterologist at the University of Calgary in Canada. While some analyses have found that this rise has plateaued during the first decades of the current century, a 2020 study in the journal Inflammatory Bowel Diseases concluded that between 2007 and 2016, the incidence of IBD in the United States more than doubled among both kids and adults. About one in 200 adults has IBD, that study concluded.

“Whatever it is causing this seems to be rooted in the westernization of society,” Kaplan says. “Something about a Western lifestyle seems to be allowing this disease to flourish.”

The likeliest culprits

GI researchers say that the rise of IBD and other gut disorders likely stems from a mix of factors. But, to a person, they agree that the much-maligned “Western diet” likely plays a starring role.

“As soon as a country is westernized, IBD starts increasing, and I think diet is absolutely contributing to that,” says Karen Madsen, PhD, a professor at the University of Alberta in Canada who studies the role of the microbiome in IBD and related diseases.

“Something about a Western lifestyle seems to be allowing this disease to flourish.”

The gut is home to trillions of microbes (aka the microbiome) that break down the foods we eat. These microbes also produce metabolites that assist in digestion, immune functioning, and other aspects of GI health. Much of Madsen’s recent research has explored the impact of dietary sugar on the microbiome and the gut’s immune activity. “When you put sugar into the diet, what happens is that you feed certain bacteria,” she says. These bacteria tend to stoke inflammation while also impeding the growth of healthy, inflammation-lowering bacteria and metabolites. A Western diet packed with heavily processed foods tends to contain a lot of simple sugars. It also lacks fiber and complex carbohydrates, which are the types of foods that support healthy bacteria populations, Madsen explains. The Western diet is likewise implicated in the development of GERD and irritable bowel syndrome.

While a high-sugar, low-fiber diet seems to imperil the gut at any age, there’s evidence that eating a lot of sugary processed foods very early in life may shift the developing microbiome in ways that encourage inflammation and dysfunction. Unfortunately, these shifts may not be reversible later in life, even if a person ditches sugar and adopts a healthier diet.

While a Western diet is a prime suspect in America’s gut woes, other candidates make the lineup.

Kaplan says that the overzealous use of antibiotics may also be a contributor. “We know that antibiotics affect the microbiome, particularly early in life,” he says. “Doctors are becoming more judicious, but there was a time when every time a kid got an ear infection, they were prescribed an antibiotic.”

He also mentions the so-called hygiene hypothesis, which has garnered significant attention and study. “The hypothesis is that in Western societies we live in a much more sterile environment,” Kaplan says. “So we’re not getting exposed to the vast number of microbes we used to, and this may not be good for us.” (Some recent work has found that the bacteria living in a person’s environment may support mental health as well as gut health.)

Other experts say that the modern world is awash in chemicals that may be disruptive to the gut. “Toxins or pollutants or pesticides — those types of exposures are more prevalent in industrialized countries and may be part of the picture,” says Berkeley Limketkai, MD, PhD, director of clinical research at the UCLA Center for Inflammatory Bowel Diseases. He also mentions stress as yet another possible contributor.

“I don’t think there’s one trigger,” Limketkai adds. “All of these independently could help explain the rise in inflammation and IBD, but I think it’s likely a constellation of them.”

Can the damage be reversed?

That’s difficult to say. If a person’s gut problems are caused by an unhealthy diet, Madsen says that trying to cut down on processed foods and sugars could be beneficial. She also recommends eating a variety of high-fiber foods like whole fruits and vegetables. But not everyone’s microbiome is malleable. “Some people’s microbes readily adapt to change, and some don’t,” she says.

It’s possible that avoiding antibiotics, ditching unnecessary consumer chemicals, and taking other steps to safeguard one’s gut health could all be beneficial. But experts say that the complexity of the gut and its relationship to the immune system defy simple, universal remedies.

“I think that in the Western world, we’re doing things to our bodies early in life — and also throughout life — that reduce the diversity and complexity of the microbiome,” Kaplan says. “Patients ask me, ‘What can I do?’ And it’s very hard to give satisfying advice.”

I write about health and science. I live in Detroit with my wife and kids. I’m trying to learn German, but my progress so far is nicht gut.

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