PARIS — A prospective European study of nearly 400,000 patients who were monitored for more than 10 years has shown that eating unprocessed or minimally processed foods, particularly fruits and vegetables, cuts the risk of developing Crohn’s disease by half. Yet this protective effect is not found among patients with ulcerative colitis.
These were the findings presented at this year’s French-language hepato-gastroenterology and digestive oncology conference (JFHOD 2023) and published in Clinical Gastroenterology and Hepatology.
“These data suggest that we should be advising our patients to consume minimally processed or unprocessed foods to cut the risk of Crohn’s disease, especially our high-risk patients, like those with a close relative suffering from the condition,” said the authors of the study, which was headed by Antoine Meyer, MD, of Bicêtre Hospital in Paris.
The study investigated the link between processed foods and the risk of developing inflammatory bowel disease (IBD), which includes Crohn’s disease and ulcerative colitis.
The consumption of ultraprocessed foods was found to be associated with an increase in the rate of Crohn’s disease, but this trend was not significant, owing to a lack of statistical power. However, a recent meta-analysis that included this study showed a statistically significant increase of 71% in the risk for Crohn’s disease associated with this type of food, Meyer said during his presentation.
In the European study, as in the meta-analysis, which collated the follow-up data of more than a million people, the consumption of processed food seemed to have an effect on the incidence of Crohn’s disease but not on that of ulcerative colitis.
The emergence of IBD coincided with industrialization, with “ulcerative colitis at first, then Crohn’s disease several decades later,” said Meyer. In addition to genetic factors, changes in diet are largely suspected of being responsible, mainly by changing the gut microbiome.
The increasing consumption of ultraprocessed, additive-rich foods that are generally low in fiber and essential micronutrients is thought to disrupt the gut’s microbiota, leading to gastrointestinal inflammation.
To explore this hypothesis, Meyer and his colleagues analyzed data from the European Prospective Investigation Into Cancer and Nutrition (EPIC) cohort, which was established in the late 1990s and involves 413,590 healthy volunteers (68% women) from eight European countries. The average age of the volunteers at the time of enrollment was 51.7 years. All participants answered a questionnaire about their dietary habits over the 12 months before enrollment.
Four Food Categories
The food products that were consumed were categorized on the basis of the extent to which the foods underwent processing (NOVA classification):
Unprocessed or minimally processed foods: food that is fresh or that has been modified by processes such as drying, pasteurization, crushing, etc (eg, fruits, vegetables, milk, natural yogurt, eggs, rice, and pasta).
Processed culinary ingredients: substances derived from group 1 foods by processes that include pressing or grinding (eg, sugar, condiments, starch, butter, and vegetable oil).
Processed foods: simple products obtained from foods and ingredients from the previous groups with the purpose of increasing their durability or enhancing their sensory qualities (eg, cheese, bread, smoked foods).
Ultraprocessed foods: products obtained industrially by mixing several ingredients. These foods may involve food additives, lyophilized proteins, modified starch, etc. They are usually rich in added sugar, salt, and saturated fat.
During the follow-up period, which lasted an average of 13.3 years, 179 cases of Crohn’s disease and 431 cases of ulcerative colitis were identified.
The analysis showed that people who consumed large amounts of unprocessed or minimally processed food (the highest quartile) were half as likely to develop Crohn’s disease (hazard ratio [HR] = 0.57; 95% CI, 0.35–0.93) in comparison with people who consumed the least amounts of these types of food (lowest quartile). This outcome was especially significant for fruits and vegetables.
For ulcerative colitis, there was a downward trend with respect to the risk of unprocessed or minimally processed foods, but the difference was not significant (HR = 0.89; 95% CI, 0.65–1.21).
In terms of consumption of ultraprocessed foods, the risk for Crohn’s disease was increased among people who consumed the most, compared with those who consumed the least (HR = 1.48; 95% CI, 0.79–2.76), but the difference was not significant. There appeared to be no impact on the incidence of ulcerative colitis.
An Unexplained Mechanism
These results have been summarized in a Canadian-led meta-analysis in which the data from five prospective studies of the link between processed food and the risk of IBD was collated. The studies that were included in the analysis involved more than a million people. Over the course of the study, 916 persons developed Crohn’s disease, and nearly 2000 cases of ulcerative colitis were diagnosed.
In this meta-analysis, the investigators showed that there was a significant link between eating ultraprocessed food and developing Crohn’s disease: the risk of developing the condition was increased by 71% among those who consumed the most ultraprocessed foods (HR = 1.71; 95% CI, 1.37-2.14) in comparison with those consumed the least. The impact was still not significant for ulcerative colitis.
The European study does have limitations. Eating habits were determined on the basis of a questionnaire that was administered at enrollment, and those habits were not reassessed. This bias meant that the links between eating habits and the risk of IBD were “underestimated,” said Meyer, “but not made up.”
The results suggest that these inflammatory diseases “probably have different mechanisms of onset,” Meyer added. He reiterated that risk factors associated with these two conditions may differ. For example, low-fiber diets favor the development of Crohn’s disease, while diets high in sugar, fatty acids, and meat are more likely to lead to the development of colitis.
Several hypotheses have been put forward to explain the excess risk for Crohn’s disease associated with consumption of ultraprocessed foods. Possibilities include an imbalance of the gut microbiota or modification of inflammatory proteins. “There is currently no argument allowing us to favor one theory over any other,” said Meyer.
This article was translated from the Medscape French Edition.