The importance of gut microbiota in the pathogenesis of obesity and its associated metabolic dysfunction has been increasingly highlighted in studies.
At the same time, dietary fibre has been linked to enhancement of carbohydrate-degrading bacteria and microbial diversity that are essential for maintaining gut homeostasis, which in turn facilitates weight loss.
To investigate the effects of dietary intervention and/or with synbiotic supplementation on gut microbiota, obesity markers, and metabolic syndrome (MetS), a randomised clinical trial was conducted in Hong Kong.
A total of 55 overweight or obese individuals were recruited from January to October 2021, and randomly assigned to three groups — synbiotic supplementation group (SG), dietary intervention group (DG), and dietary intervention with synbiotic supplementation group (DSG).
During the eight-week trial, DG and DSG followed an eating plan, with the goal of consuming 30 ± 5g of dietary fibre from fruits and vegetables per day.
Participants were allowed to consume an ad libitum diet, except for the intake of fruits and vegetables. Their dietary records were checked weekly by nutritionists to ensure compliance.
The synbiotic supplement provided to SG and DSG contained a mixture of probiotics (Bifidobacterium lactis HN019 and Lactobacillus acidophilus NCFM), and a prebiotic (polydextrose or PDX) packed in a sachet.
They were instructed to take two sachets in the morning and evening every day.
Based on intergroup comparisons, the decrease in body weight, BMI, body fat mass, and trunk fat mass were significantly more pronounced in DSG than DG and SG.
In addition, the relative decrease in visceral fat rating was also markedly greater in DSG, compared to that in SG and DG.
Notably, no participants in SG lost more than 5% of their initial weight, whereas approximately 22% and 50% of the participants in DG and DSG achieved weight loss of at least 5% respectively.
By the end of the study, only DSG lost 5% body weight on average, which could potentially fulfil the criterion of clinically significant weight loss if maintained after one year.
The risk factors for MetS were assessed based on parameters including fasting glucose, fasting insulin, high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG) levels.
Compared to baseline, a significantly greater decrease in fasting glucose was shown in DSG but not in SG and DG, while fasting insulin and insulin resistance levels were significantly lowered in DG and DSG.
Impact on gut microbiota
Profiling of the gut microbiota was done on collected faecal samples using 16S rRNA gene sequencing.
Although there was no significant difference in Firmicutes-to-Bacteroidetes (F/B) ratio and Shannon diversity index between the three groups, it is noteworthy that F/B tended to decrease in DSG after intervention (p = 0.053).
“Another important finding is that Megamonas is significantly and positively associated with BMI, body fat mass, and trunk fat mass in DSG but not in DG, suggesting that the synbiotic supplement enables Megamonas to become a key genus responsible for amplifying the anti-obesity effects of the diet.
“On top of the marked decrease in Megamonas, it is hypothesised that the elevated abundance of acetate-producing Parabacteroides could mediate the anti-obesity response in a diet-specific manner,” the authors wrote.
In previous studies, PDX was shown to enhance the intestinal barrier function in people with severe acute pancreatitis due to the stimulation of mucin production, which strengthens intestinal epithelial tight junctions.
As intestinal permeability is associated with BMI, body fat mass, and visceral adiposity, the substantial improvement in intestinal permeability resulting from PDX-containing synbiotic supplementation might be a possible mechanism to explain the biggest reduction in obesity observed in DSG.
“Increasing consumption of fruits and vegetables should be targeted as the most important nutritional variable for primary consideration in a dietary intervention for weight loss.
“Our findings support the fact that the synergistic action of a high-fibre diet and synbiotic supplementation could lead to favourable changes in the gut microbiota and obesity indicators,” the authors wrote.
While the results indicated that the use of a synbiotic supplement alone had no significant influence on body composition and metabolic biomarkers, a longer intervention period may be needed to demonstrate the real weight-loss effects of synbiotics.
Counteracting side effects of high dietary fibre intake
Fruits and vegetables are reportedly consumed at an inadequate level by the Hong Kong population, among which 29.9% aged 15 to 84 were obese (BMI ≥ 25 kg/m2).
A lack of dietary fibre could increase the risk of gut barrier dysfunction due to intestinal mucus erosion.
In this study, the eating plan increased the intake of fruits and vegetables based on the Healthy Eating Food Pyramid in Hong Kong.
These foods possess a wide range of phytochemicals that could also modulate the gut microbiota, bringing about anti-obesity, anti-inflammatory, and lipid-lowering effects.
“Although high dietary fibre intake may contribute to weight loss via increased satiety, and gastrointestinal discomforts such as bloating, abdominal pain, and constipation, these side effects may hinder adherence to the diet plan in the long run, therefore an effective yet comfortable dietary intervention is critical for well-being.”
It was observed during the trial that these gastrointestinal issues were reported by some participants in DG, when adapting to the increased dietary fibre intake at the early phase of intervention.
This phenomenon was not observed among participants in DSG, who increased consumption of fruits and vegetables without feeling any discomfort.
It should be noted that the study has several limitations, including a small sample size, uneven gender distribution of participants, short trial period, absence of a placebo group, and risk of bias in the self-reported dietary data.
“We were unable to identify the two probiotic species in the faecal samples of SG and DSG participants due to the limitation of 16S rRNA gene sequencing, which can only detect the identity of bacteria up to the genus level.
“Nevertheless, the difference in weight loss percentage between DG and DSG is noteworthy and clinically meaningful. Moreover, the strong adherence demonstrated by the participants, which is crucial for any weight loss diet or programme, can be attributed to the simplicity of our intervention,” the authors concluded.
“Effects of Synbiotic Supplementation on Metabolic Syndrome Traits and Gut Microbial Profile among Overweight and Obese Hong Kong Chinese Individuals: A Randomized Trial”
Authors: Susana Lauw, et al