Adults with obesity who consumed a dietary fiber supplement had positive effects on high-density lipoprotein cholesterol (HDL-C) and mood outcomes. However, the eight-week trial showed no additional beneficial effects from combined probiotic supplementation.
“Rather than indicating that synbiotic strategies are ineffective, the present results suggest that the effect of a combined intervention may depend partly on whether the selected prebiotic is actually suitable for the probiotic strains used,” wrote researchers in China and Taiwan in Nutrients.
“In this sense, choosing an appropriate prebiotic may be just as important as choosing the probiotic itself.”
Nearly 28% of adults worldwide have metabolic syndrome, which is a cluster of conditions including high blood pressure, abdominal obesity, insulin resistance, and abnormal cholesterol levels.
Dietary manipulation of the gut microbiota may be a promising strategy for addressing obesity and metabolic syndrome, and previous studies have also demonstrated benefits for mental health and sleep.
Dietary fiber acts as a prebiotic, which gut bacteria ferment to produce short-chain fatty acids that may help regulate inflammation and metabolic syndrome.
To date, there is limited evidence to assess the independent effects of prebiotic and probiotic supplementation in metabolic disorders, which the current study aimed to address by looking at individual and combined supplementation strategies.
Study details
The study participants were 55 adults with obesity, defined as body fat percentages over 25% in men and 30% in women rather than just their body mass index.
They were randomly assigned to receive either dietary fiber, a probiotic, a combination of dietary fiber and probiotic, or a placebo daily before breakfast for eight weeks.
The probiotic was a multi-strain capsule containing Lactobacillus plantarum, Bifidobacterium longum, Lactobacillus rhamnosus, and Streptococcus thermophilus, and the dietary fiber supplement was indigestible dextrin.
The researchers made anthropometric assessments and evaluated blood pressure and biochemical markers before and after the interventions, and participants completed questionnaires about mood and sleep. Statistical analysis was performed using appropriate methods.
The results showed that after statistical correction, HDL-C was the only metabolic syndrome-related outcome that remained significant for dietary fiber.
“Similarly, probiotic supplementation showed an uncorrected association with higher HDL-C, but this effect was no longer significant after FDR [False Discovery Rate] correction,” the researchers wrote.
They noted that the effects on mood disturbance were more pronounced than the metabolic outcomes.
“In the present study, dietary fiber supplementation was associated with significant reductions in total mood disturbance and improvements in several negative mood dimensions, including confusion, fatigue, anger, tension, and depression,” they wrote, noting that in contrast, probiotics did not show significant effects.
There were some positive effects of fiber on sleep outcomes, which the researchers described as weak evidence and cautioned that these findings should be regarded as exploratory.
With no additional effects of combined supplementation observed, the researchers suggested that “the effectiveness of synbiotic strategies may depend on the compatibility between the selected dietary fiber and probiotic strains.”
They acknowledged their study limitations, calling for future larger, longer trials with dietary monitoring and direct mechanistic measures.
Source: Nutrients 2026, 18(12), 1851; https://doi.org/10.3390/nu18121851, “Effects of Probiotic and Dietary Fiber Supplementation on Metabolic Syndrome-Related Features, Mood, and Sleep in Adults with Obesity.” Authors: J. wang et al.
