A current challenge in gut microbiome science is that of characterizing the effects of food groups on gut microbial communities instead of focusing on isolated nutrients. Although prebiotics provide health benefits by specifically altering the composition or activity of the gut microbiota, not all dietary fibers are prebiotics and they can benefit gut bacterial groups in different ways.
A new study, led by Dr. Nathalie Delzenne from UC Louvain in Brussels (Belgium), has found that regular consumption of vegetables rich in inulin-type fructans improve food behavior and are well tolerated overall, through changes in the gut microbiota.
Hiel and colleagues explored the impact over time of daily consumption of vegetables rich in inulin-type fructans on the gut microbiota, gastrointestinal symptoms and food-related behavior in 26 healthy normal weight adults.
The nutritional intervention consisted of a diet enriched in vegetables rich in inulin-type fructans for 2 weeks. Examples of natural foods with a high fructan content that were included in the participants’ daily ready-made meals were Jerusalem artichokes, garlic, salsify, onion, shallots and leeks.
The consumption of a mean intake of 15 grams/day of fructans led to decreased gut microbiota richness and changes at the taxa level, including an increased proportion of the Bifidobacterium genus, which was negatively correlated with fiber intake; a decreased level of unclassified Clostridiales, Alistipes and Oscillibacter genus; and an increase in the Prevotellaceae family. However, the changes observed in gut microbiota composition were reversed 3 weeks after the subjects returned to their usual diet. These findings therefore highlight the importance of regular consumption of a fermentable fiber-rich diet in order to maintain the beneficial effects on gut microbiota composition.
The intervention did not lead to a significant change in gut microbiota activity, which was assessed using microbial fermentation both in vivo and in vitro.
The regular intake of vegetables rich in inulin-type fructans was accompanied by higher levels of satiety and a reduced preference for sweet and salty foods, which persisted for 3 weeks after the end of the study. Other than this, participants also showed a trend toward preferring salsify at the end of the intervention, whereas the preference for other vegetables remained stable throughout the study.
The nutrition intervention was, on the whole, well tolerated. Episodes of flatulence were the only thing reported during the dietary intervention, which showed associations between fecal bacteria and flatulence, nausea, burping, discomfort, and rumbling. Flatulence among participants improved, however, after 3 weeks of dietary reversion.
GMFH editors corresponded with the lead author Nathalie Delzenne to clarify the relevance of the findings for clinical practice among healthcare professionals:
“We are showing for the first time that it is possible to get specific changes in microbiota composition and changes in food behavior (including a drop in preference for fat, salt or sugars) by regularly eating vegetables that are naturally rich in inulin-type fructans. Those vegetables are well tolerated and even allow the gut to adapt to fibers, thereby decreasing some of the sensations linked to bacterial fermentation. Such a dietary approach can thus be part of nutritional advice for maintaining and recovering health. Current perspectives include testing such a nutritional approach in obesity and related metabolic disorders.”
Hiel S, Bindels LB, Pachikian BD, et al. Effects of a diet based on inulin-rich vegetables on gut health and nutritional behavior in healthy humans. Am J Clin Nutr. 2019; 109(6):1683-95. doi: 10.1093/ajcn/nqz001.