A diet rich in fish, especially those containing high amounts of long-chain polyunsaturated fatty acids (PUFAs), might reduce the risk of inflammatory bowel disease, a review study suggests. But further studies are needed to fully understand this association.

The study, “Dietary intake of fish, n-3 polyunsaturated fatty acids, and risk of inflammatory bowel disease: a systematic review and meta-analysis of observational studies,” was published in the European Journal of Nutrition.

Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn’s disease (CD), is caused by an excessive immune reaction against the gut flora, which leads to chronic inflammation of the gastrointestinal tract. The response might be triggered by genetic, environmental — mainly diet — and physiological factors.

High consumption of fish could affect the risk of developing IBD, as fish are rich in PUFAs, a kind of polyunsaturated fat reported to regulate the inflammatory response.

However, the available studies on the association between fish and PUFAs consumption and risk of IBD are contradictory. Therefore, a review study was performed to clarify this association.

The authors evaluated the results of 10 previous studies that together assessed 213,584 people, 1,691 of whom were IBD patients (905 CD and 786 UC). The studies had different sample sizes and experimental designs and were performed in different countries.

The authors found a slightly negative association between fish consumption and IBD, meaning that fish consumption might slightly reduce the risk of developing IBD. However, fish consumption had a significant positive impact on CD when the condition was considered independently.

There was no relationship between dietary PUFA and IBD, either CD or UC. However, researchers found that a diet rich in PUFAs of greater size, called long-chain PUFAs, could protect from IBD development, especially UC. This result makes sense as long-chain PUFAs are stronger modulators of the inflammatory response than their smaller counterparts.

Although not all the studies reported beneficial effects of fish and long-chain PUFAs, those that did had the best experimental design and considered confounding factors such as other dietary components, body mass index, and smoking.

“There was an inverse association between fish consumption and the risk of CD. Moreover, an inverse association was observed between dietary long-chain n-3 PUFAs intake and the [risk] of UC. Additional well-designed studies, considering subtypes of fish and n-3 PUFAs, are needed,” researchers said.