Sugar: The Gut-Wrenching Truth
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For years, researchers have suspected that the typical Western diet plays a leading role in the high rates of inflammatory bowel disease (IBD) observed in industrialized countries around the world.
But what exactly about the Western diet — high in fat, animal protein, and sugar, and low in vegetables, legumes, whole grains, and fruit — is to blame? While fat and animal protein have traditionally been considered the prime suspects, a growing number of studies now point to sugar as a leading culprit.
In a study published in February 2016 in Inflammatory Bowel Diseases, researchers found a positive association between a “high sugar and soft drinks” eating pattern and risk of ulcerative colitis (UC). The study — the largest of its kind, involving 366,351 participants from several European countries — also determined that high vegetable intake modulated UC risk, even among high consumers of sugar and soft drinks.
“The rapid increase in the incidence of both Crohn’s disease and ulcerative colitis over the past 50 years and the geographic distribution of patients with IBD … support the role of environmental factors in the etiology of IBD, of which diet could be an important part,” the study authors wrote.
The authors also noted their interest in the “North–South gradient” in IBD risk—in other words, the higher IBD rates observed in northern European countries where a Western diet is more common and lower IBD rates in southern European countries, which tend to follow a Mediterranean diet, rich in vegetables, legumes, fruits and nuts, cereal products, fish and olive oil.
Sugar May Damage Gut Microbiome
Sugar is already well known for its pro-inflammatory effects on the body and its link to a number of diseases, including cardiovascular disease, obesity, cancer, and type 2 diabetes. And while the precise nature of the relationship between sugar and IBD remains unsettled, more and more data from animal studies points to sugar’s deleterious effects on the gut microbiome.
A study published in October 2020 in Science Translational Medicine found that mice who consumed a 10 percent sugar solution for a week (less than the typical 15 percent contained in most soft drinks) significantly altered the composition of gut microbiota — in a bad way. Two types of mucus-degrading bacteria became more abundant, leading to erosion of the gut’s protective mucus layer, while quantities of “good” bacteria, like Lactobacillus, diminished, effectively setting the stage for colitis.
“The United States has one of the highest sugar-consuming populations in the world,” says Hasan Zaki, PhD, an assistant professor of pathology at University of Texas Southwestern Medical Center in Dallas, who led the study. “Our research shows that high sugar intake may also be contributing to rising rates of IBD.”
Dr. Zaki notes that the rise in IBD over the last few decades parallels the rise in consumption of high-fructose corn syrup (HFCS), the leading sweetener in soft drinks and a variety of processed foods, including even some deemed “healthy,” like sweetened yogurt and granola bars. HFCS has already been linked with the epidemics of obesity and type 2 diabetes.
Meanwhile, as much as the presence of sugar in the Western diet appears to be a critical culprit in IBD, the absence of certain nutrients may also be to blame. As the researchers in the European study found, low vegetable intake raises the risk of ulcerative colitis among high consumers of sugar and soft drinks.
Fiber Fuels Beneficial Bacteria
Once again, the action seems to take place at the gut level: While sugar has been shown to damage the gut microbiome, vegetables — and specifically the fiber they contain — have been shown to do good. And in the case of IBD, there may be a direct correlation. “Vegetable intake seems to neutralize the harmful effects of soft drinks in UC,” the European study authors wrote. So, if vegetables confer protection, their absence raises risk.
Diets lacking in fiber have been associated with an increased risk of heart disease, cancer, obesity and type 2 diabetes, while fiber-rich diets have been shown to be protective. The same may hold true for IBD.
“Fiber-rich foods act as fuel for the beneficial bacteria that live in the gut,” explains Karen Madsen, PhD, the director of the Center of Excellence for Gastrointestinal Inflammation and Immunity Research at the University of Alberta in Edmonton. Dr. Madsen conducted a study, published in August 2019 in Scientific Reports, on the risks of sugar binges in IBD. She says that some beneficial bacteria produce short-chain fatty acids (SCFAs), which play a critical role in gut health.
In addition to acting as a preventive of IBD, SCFAs may provide relief after damage has occurred. Madsen’s study found that mice who displayed intestinal damage and a defective immune response as a result of consuming a high-sugar, low-fiber diet experienced an improvement in symptoms when their diet was supplemented with SCFAs.
Patient surveys, such as those used in a study published in Clinical Gastroenterology and Hepatology in May 2020, seem to echo the findings: Among people diagnosed with ulcerative colitis, those who switched to a diet containing more vegetables, fruit, and fiber reported improved well-being and higher quality of life. And those who reduced their intake of fat in addition did even better, displaying less inflammation and healthier gut microbiota. While people in the midst of a UC flare are often advised to reduce fiber intake, the recent data indicate they may be missing out if they do so all the time.
Short-chain fatty acids, which are produced when insoluble fiber from dietary plant matter ferments in the gut, have been shown to exert a variety of health benefits, including a stabilizing of blood sugar and a reduction of systemic inflammation.
Fiber-rich foods like vegetables, legumes, whole grains, and fruits — mainstays of the Mediterranean diet — all encourage the production of short-chain fatty acids. And they’re just what a Western diet, with its taste for high-sugar foods and drinks, is missing.
The average American consumes about 17 teaspoons (tsp) of added sugars per day in foods and drinks, according to scientists at the University of California in San Francisco. The American Heart Association recommends no more than 6 tsp of added sugar daily for women and 9 for men.
Considering that a single 12-ounce can of Coke contains nearly 8 tsp of added sugar, it’s not difficult to see just how easy it is to exceed the limit. On the other hand, a simple change like ditching soda goes a long way. “The unhealthy level of sugar in daily American life is a huge problem,” Zaki says. “We may not be able to avoid sugar completely, but we can certainly lower the dose.”