How dietary fiber leaves its mark within the gut: Just 2 weeks are enough for dietary fiber to influence microbial metabolism

In normal conditions, meal ingestion induces satiation and fullness which, depending on the type of foods ingested, individual sensitivity and reflex activity, may have a pleasurable dimension leading to digestive well-being. However, 84% of people with IBS experience digestive symptoms related to food intake, including abdominal pain, bloating and abdominal distension, which are not secondary to structural abnormalities in their digestive tract.

The study of factors that determine digestive sensations is currently an active area of research for scientists such as those at the University Hospital Vall d’Hebron in Barcelona, Spain.

A new cross-over, randomized study, led by Dr. Fernando Azpiroz from the Digestive System Research Unit at University Hospital Vall d’Hebron, elucidates how diet influences gut microbiota composition and metabolic activity, colon biomass and perception of digestive sensations in healthy individuals.

The authors administered a high-fat and low-residue diet (Western-type diet; 4.7 g fiber from food sources) versus a low-fat and high-residue diet (fiber-enriched Mediterranean diet; 54.2 g fiber from food sources) for two weeks in 20 healthy men after a period of two weeks on a balanced diet. Thus, all participants received both interventions, but the order in which they were received was randomized.

Although the two diet types were well tolerated, leading to a sensation of digestive well-being, the fiber-enriched Mediterranean diet led to high scores of flatulence and rumbling sounds caused by gas moving through the intestines and a higher number of anal gas evacuations. Stool consistency, stool weight and colonic content were also higher in participants on the fiber-enriched Mediterranean diet.

Although at the gut microbiota composition level some genus and species were enriched in participants who followed the fiber-enriched Mediterranean diet, a core gut microbiota was shared regardless of dietary intervention.

In contrast, both diets had a notable effect on gut microbiota metabolic activity. As such, a total of 27 metabolic pathways showed higher expression following the fiber-enriched Mediterranean diet. It is interesting to note that not all the genomes found in gut microbial communities were influenced in the same way by diet. For example, the fiber-enriched Mediterranean diet led to a gut microbiome with high diversity and enriched in up to 1322 gene families with a less anal gas evacuation in participants with a gut microbiota that did not change after each intervention (i.e., robust gut microbiota).

The results suggest that the metabolic capacity of the gut microbiome might adapt to dietary substrates so dietary fiber does not necessarily be the culprit of symptoms in all people. While patients with gut-brain interaction disorders such as irritable bowel syndrome usually exclude fiber from their diet as means to improve symptoms, the current findings show this choice could not relate to anal gas evacuations in a subset of people.

A short period of two weeks was enough time for the gut microbiota to adapt to dietary substrates, which highlights the importance of evaluating in a personalized way the need to exclude dietary fiber for managing digestive issues. Indeed, a small amount (10 g) of fiber daily has been shown to be enough to selectively promote the growth of beneficial Bifidobacterium species in the gut. Furthermore, a previous intervention study showed that low-dose prebiotics were superior to the known exclusion FODMAP diet for managing digestive symptoms, suggesting that digestive symptoms can be alleviated by modulating the metabolic activity and composition of the intestinal microbiota with diet.

In conclusion, the findings show that although diet does not always lead to changes in gut microbiota composition, it can have a profound effect on gut microbial metabolic functions. That, in turn, can have implications for healthy subjects and patients with digestive symptoms with no detectable abnormalities according to conventional diagnostic methods.

References:

Böhn L, Störsrud S, Törnblom H, et al. Self-reported food-related gastrointestinal symptoms in IBS are common and associated with more severe symptoms and reduced quality of life. Am J Gastroenterol. 2013; 108(5):634-641. doi: 10.1038/ajg.2013.105.

Barber C, Mego M, Sabater C, et al. Differential effects of Western and Mediterranean-type diets on gut microbiota: A metagenomics and metabolomics approach. Nutrients. 2021; 13(8):2638. doi: 10.3390/nu13082638.

So D, Whelan K, Rossi M, et al. Dietary fiber intervention on gut microbiota composition in healthy adults: A systematic review and meta-analysis. Am J Clin Nutr. 2018; 107(6):965-983. doi: 10.1093/ajcn/nqy041.