Treatment options for people with irritable bowel syndrome (IBS) are limited and diet plays an important role in symptom management. While some food items, such as carbohydrates that are incompletely absorbed in the small intestine, can trigger IBS symptoms, there is no optimal dietary advice that works for everyone. Aware of the importance of diet in managing IBS, some scientific societies such as the British Society of Gastroenterology recently launched new guidelines on managing IBS that consider dietary advice, together with regular exercise, as first-line treatment in all patients with IBS.
Although certain gut microbiome profiles have been linked to the severity of IBS symptoms, little is known about the role of diet in shaping gastrointestinal symptomatology through the gut microbiome.
A new study, led by Muriel Derrien and Magnus Simrén, shows that poor diet quality and gut microbiome composition and functions are associated with IBS gastrointestinal symptom severity.
The authors used a novel approach that combined data from a 4-day food diary and gut microbiota composition and functional genes in 149 individuals with IBS, of whom almost half had severe symptoms, along with 52 healthy controls. In order to consider both diet quantity and quality, foods were categorized into a food tree based on the Swedish Food Composition Database and a Dietary Index score was developed in which a higher score reflected lower nutritional quality.
Consumption of meat-based foods versus plant-based foods was the major driver in distinguishing dietary patterns among participants. While no differences emerged at macro- and micronutrients levels between individuals with IBS and healthy controls or between patients with IBS with different levels of symptom severity, the authors found that those with more severe gastrointestinal symptoms showed a higher intake of poor-quality food staples (i.e., processed food items such as candy, soft drinks and fried potato products).
The authors went a step further and explored the relationships between diet and gut microbiota composition and function. Participants’ diets showed associations with gut microbiota composition at species and subspecies level. New associations were found between gut microbiota subspecies and diet. For instance, Eubacterium rectale subspecies were linked to a predominantly meat-based diet. Furthermore, complex statistical analyses revealed that plant- and animal-based diets and the gut microbiota are related to IBS symptom severity and to altered gut microbiota hydrogen function.
As carbohydrates are the foods often associated with a worsening of IBS symptoms due to gas generation after their fermentation in the colon, the authors were also interested in learning more about the relationship between microbial enzymes involved in metabolizing dietary carbohydrates and IBS symptom severity. A higher abundance of microbial enzymes involved in metabolizing food glycans—especially glycans associated with meat or mucins—was associated with the abundance of hydrogenases involved in the production of hydrogen in the colon during microbial fermentation of carbohydrates. Interestingly, individuals with severe IBS symptoms had a higher abundance of a specific type of hydrogenase known as hydrogenase [FeFe] A3, which emerges as a potential microbiome biomarker useful to monitor in IBS.
On the whole, the study reveals that IBS severity is related to gut microbiota composition and function along with changes in microbial enzymes involved in dietary carbohydrate metabolism. The findings indicate the role of specific gut microbiome profiles in mediating the effects of diet on IBS symptom severity, with low-quality food products and altered carbohydrate fermentation by the gut microbiota being major triggers for gastro-intestinal symptoms.