An analysis of data from the European Prospective Investigation into Cancer (EPIC) study found an association between high consumption of sugar and soft drinks, together with low consumption of vegetables, and risk of ulcerative colitis (Inflamm Bowel Dis. 2016;22[2]:345-54.). A subsequent analysis of data from two prospective Swedish cohorts, however, found no association between consumption of sugary beverages and risk of Crohn’s disease or ulcerative colitis (Clin Gastroenterol Hepatol. 2019;17[1]:123-9.).
Although the data on sugar are mixed, data on the association between other macronutrient groups and risk of IBD are more consistent. When Dr. Ananthakrishnan and colleagues examined data from the Nurses’ Health Study, they found that the highest quintile of dietary fiber intake was associated with a 40% reduction in risk of Crohn’s disease, compared with the lowest quintile. The observed reduction of risk seemed to be greatest for fiber derived from fruits. Fiber from cereals, whole grains, or legumes, however, did not affect risk of Crohn’s disease (Gastroenterology. 2013;145[5]:970-7.).
A separate analysis of the Nurses’ Health Study suggested that high intake of n-3 polyunsaturated fatty acids (PUFAs) and low intake of n-6 PUFAs was associated with a 31% reduction in risk of ulcerative colitis and a 15% reduction in the risk of Crohn’s disease. These data were consistent with a previous analysis of EPIC data that found that high intake of n-6 PUFAs was associated with increased risk of ulcerative colitis (Gut. 2009;58[12]:1606-11.). Other analyses indicate that genetic polymorphisms likely modify the association between PUFAs and risk of ulcerative colitis, said Dr. Ananthakrishnan. “There may be an additional layer of complexity beyond just measuring your dietary intake.”
In addition to macronutrients, micronutrients can modify a patient’s risk of ulcerative colitis or Crohn’s disease. When Dr. Ananthakrishnan and colleagues examined the Nurses’ Health Study, they found an inverse association between vitamin D intake and risk of Crohn’s disease (Gastroenterology. 2012;142[3]:482-9.). In a separate study, they found that a zinc intake greater than 16 mg/day was associated with reduced risk of Crohn’s disease (Int J Epidemiol. 2015;44[6]:1995-2005.).
Patients aged older than 40 years and patients of European ancestry tend to be overrepresented in cohort studies, which reduces the generalizability of their conclusions, said Dr. Ananthakrishnan. Furthermore, cohort studies have not produced consistent findings regarding the relationship between various dietary components and risk of IBD. Nevertheless, the data suggest that dietary patterns may be associated with incident Crohn’s disease or ulcerative colitis.
An influence of diet on IBD risk is plausible
One mechanism through which diet may exercise a causal influence on the risk of IBD is by affecting the microbiome. In 2011, investigators studied 98 healthy volunteers who answered questionnaires about their diet. The researchers also used 16s rDNA sequencing to characterize the population’s stool samples. A diet high in animal protein, amino acids, and saturated fats was associated with large populations of Bacteroides. A diet low in fat and in animal protein, but high in carbohydrates and simple sugars was associated with large populations of Prevotella. When the investigators conducted a controlled-feeding study of 10 patients, microbiome composition changed within 1 day of initiating a high-fat-and-low-fiber or a low-fat-and-high-fiber diet (Science. 2011;334[6052]:105-8.). A more recent study showed that the diversity of the microbiome increased with the adoption of an animal-based diet (Nature. 2014;505[7484]:559-63.).
