Beneficial effects of plant-based diets on gut microbiome composition

Aim

Plant-based diets have become more and more popular worldwide due to their positive effects on the environment and human health.

Plant-based diets have been linked in a number of studies that lower risk of obesity, cardiovascular disease, and other health conditions. 

This study investigated the effects of various plant-based diets on the composition of gut microbiota as this has shown to play an essential role in our health, predicting the risks of developing certain gastrointestinal diseases.

Method

This study design was a systematic review, following PRISMA guidelines. Types of reviews included were intervention studies, including randomized controlled trials, non- randomized trials, and pre–post interventions that reported on the effects of plant-based diets on gut microbiota.

The gut microbiota must have been quantified from stool samples that target the 16s ribosomal RNA gene utilising any sequencing technique and studies that identify the roles of microbial metabolites using liquid gas chromatography. Excluded were studies that reported a single food type.

Primary outcomes were bacterial abundance and diversity with secondary outcomes being metabolic parameters and weight.

Key findings

12 studies were included in this systematic review.  Sample size of included studies ranged from 6 to 168 with a total of 583 participants.

Geographical origins included studies from Europe, United States and Asia. Age ranges were between 21 and 61 years with study duration from 5 days to 13 months.

Studies demonstrated the positive effects of a plant-based diet on the link between gut microbiota and metabolic syndrome, and changes to the gut microbiota happening quite rapidly. From switching to either a plant-based or animal-based diet, the changes in the gut microbiota were visible within five days.

In a study including adults with rheumatoid arthritis, a one-month switch to a plant-based diet was enough to significantly change the faecal microbiota. The diet changes also caused some rheumatoid arthritis patients to have less disease activity, concluding that changes in the faecal microbiota and its disease activity are linked through diet.

Infographic showing the impact of diet on the composition of gut microbiota

The intervention studies included in the review reported an increase in the butyrate-producing bacteria, such as Ruminococcaceae, Lachnospiraceae, Coprococcus, Roseburia, Blautia, Alistipes and Faecalibacterium prausnitzii.

Butyrate has multiple physiological activities, including providing energy to colonocytes and improving the intestinal barrier via the upregulation of tight junctions. Butyrate lowers systemic inflammation by preventing lipopolysaccharide from crossing the intestinal wall and entering the bloodstream.

Substantial evidence shows that acetate, propionate, and butyrate have a preventive effect against various diseases, including type 2 diabetes, inflammatory bowel disease, and immunological diseases.

Although the authors could not provide a comprehensive conclusion on the mechanism behind gut microbiota interactions in plant-based diets, an increase in SCFA-butyrate metabolizing pathway could be a possibility. 

Conclusion

This systematic review suggests nutrition is an important determinant in the makeup of the human gut microbiota. Research suggests that switching to a plant-based diet may help increase the diversity of health-promoting bacteria in the gut.

However, due of their complexity and individual variability, further study is required to characterise the relationships among nutrition, the microbiome, and health effects.

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