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Temporary shifts: Trial suggests diet-induced microbiome changes do not last

By Will Chu

- Last updated on GMT

©iStock/Stuart Jenner
©iStock/Stuart Jenner
Eating more inulin-type fructans (ITF) found in vegetables can lead to beneficial changes in our gut microbiota composition and function, but only for a short while, say Belgium researchers.

In a small trial involving 26 subjects, those that ate hot food for lunch and dinner, prepared with ITF-rich vegetables such as Jerusalem artichoke, spinach and leek, had a gut microbiota with increased numbers of the Bifidobacterium​ genus and a decreased level of unclassified Clostridiales​.

Further results found decreased numbers of Oxalobacteraceae​. Furthermore, when subjects ceased with the diet, the changes proved temporary as gut profiles reverted to pre-trial populations.

“Three weeks after the end of the intervention, the Bifidobacterium genus, Oxalobacteraceae family, and unclassified Clostridiales returned to preintervention levels,”​ the study highlighted.

“These results underline the importance of continuing to consume a fibre-rich diet in order to maintain the beneficial effects on gut microbiota composition.”

The affected bacterial populations may explain how these ITF-rich vegetables exert their heath benefits on the human body.

In parallel with increased bifidobacteria​ levels in the gut that relates to better body weight control and cholesterol level management, beneficial health effects for Oxalobacter formigenes​ relates to a lower risk of kidney stone formation.

Clostridiales​ order has been shown to increase following a high-fat diet in rats. The team think its decrease may be related to greater consumption of vegetables.

Single group-design trial

Researchers from the The Université catholique de Louvain in Belgium devised a single group-design trial, where 26 healthy individuals were enrolled.

During a two-week period, the participants adhered to a controlled diet based on ITF-rich vegetables that provided a mean intake of fifteen grams (g) ITF per day.

In total, three test days were organised: before and after the nutritional intervention and three weeks after returning to their usual diet.

The vegetables included in the trial included ready-made meals that contained Jerusalem artichokes, garlic, salsify, onion, shallots and leeks.

The team assessed nutrient intake, food-related behaviour, faecal microbiota composition, microbial fermentation, and gastrointestinal symptoms.

Findings revealed an increased proportion of the Bifidobacterium​ genus, a decreased level of unclassified Clostridiales​, and a tendency to decrease Oxalobacteraceae​.

The researchers found these changes in the gut were reversed three weeks after the intervention.

“The volunteers showed greater satiety, a reduced desire to eat sweet, salty, and fatty food, and a trend to increase hedonic attitudes towards some inulin-rich vegetables,”​ the study noted.

“Only flatulence episodes were reported during the dietary intervention, whereas intestinal discomfort, inversely associated with Clostridium cluster IV and Ruminococcus callidus, was improved at the end of the intervention.”

EFSA recommendations

Current guidelines by the European Food Safety Authority (EFSA) recommends that healthy adults consume a minimum of 25g of fibre per day.

Studies estimate that at least 12g of ITF should be consumed to maintain adequate intestinal transit function.

In discussing the changes in food preferences the team pointed to evidence that identifies the gut microbiota composition as a diet modulator. However, it remains unclear whether the actual microbiota can drive food preferences.

Few studies highlight the ability of the microbiota to change food preferences by altering the expression of taste receptors.

The team thought prebiotic supplementation could lead to specific microbiota modification, resulting in adapted food choices.

“The overall composition of the gut microbiota remained stable throughout the intervention, but we observed a decrease in richness,”​ the team concluded.

They cited a recent study that showed prebiotic supplementation in individuals with type 2 diabetes mellitus decreases gene richness in addition to a significant clinical improvement.

Source: The American Journal of Clinical Nutrition

Published online: doi.org/10.1093/ajcn/nqz001

“Effects of a diet based on inulin-rich vegetables on gut health and nutritional behaviour in healthy humans.”

Authors: Sophie Hiel et al.

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