This study aimed to assess the effects of symbiotic supplements consisting of seven bacterial strains at a dose of 2 × 108 CFU/day and a prebiotic FOS in one capsule for 12 weeks. This study revealed that after symbiotic treatment, there was a significant decrease in BMI, waist circumference, and FBG levels, whereas HDL levels significantly increased. Conversely, HbA1c levels significantly increased in the placebo group. Before the intervention, HbA1c levels in the placebo group ranged from 6.5% to 11.47%, with 12 (40%) of patients having uncontrolled diabetes (HbA1c > 7.5%). After the intervention, HbA1c levels in the placebo group ranged from 6.5% to 11%, with 13 (43.3%) of patients still having uncontrolled diabetes. Similarly, before the intervention, HbA1c levels in the symbiotic group ranged from 6.5% to 12.73%, with 11 (35%) patients having uncontrolled diabetes. After the intervention, HbA1c levels ranged from 5% to 11.8%; however, the same number [11] and percentage (35%) remained uncontrolled which may explain the negligible effect size.
Cholesterol synthesis and absorption mainly occur in the intestine; therefore, the intestinal microflora profoundly affect lipid metabolism. Several mechanisms have been suggested for cholesterol reduction by probiotics, including the removal of cholesterol by assimilation during growth, the binding of cholesterol to the cellular surface by non-growing or dead Lactococcus cells, and the deconjugation of bile acids [28]. Additionally, the gut microbiome promotes energy absorption by enhancing the synthesis of triacylglycerols and inhibiting the oxidation of fatty acids, potentially affecting the energy balance of the human body, and leading to insulin resistance. The intestinal microflora produces several inflammatory mediators, such as lipopolysaccharides and branched-chain amino acids (BCAAs). BCAAs activate the body’s immune response, whereas inflammatory mediators activate Toll-like receptor 4, reducing sensitivity to insulin [29].
A systematic review found fair evidence that interventions with prebiotics, especially oligofructose-enriched inulin, may improve metabolic and inflammatory biomarkers related to T2DM and reported improvements in glycaemia, and body weight [30].
Another review provided evidence from various studies on the ability of prebiotic consumption to alter gut microbial profile, improve gut microbial metabolism and function, and improve host physiology to alleviate diabetes and obesity. FOS shows great potential due to its prebiotic activity and low caloric value. Additionally, a diet supplemented with FOS promotes the production of butyrate, which influences lipid metabolism in humans [31].
Similar findings were reported in a meta-analysis by Dixon et al., which found statistically significant pooled effects of probiotics in reducing BMI and serum glucose levels and increasing HDL levels. However, in contrast to our findings, this study reported significant reductions in HbA1c and TC levels. Subgroup analysis revealed that the reduction was not significant when symbiotics were administered in capsule formulations and at doses < 1.0 × 109 CFU, which is consistent with the approach used in our study. The reduction in LDL levels was apparent in predominantly female patient groups and those receiving higher dosages (> 1.0 × 109 CFU) [32].
In contrast to our findings, Mo R et al. found that probiotic interventions reduced TC and LDL levels but exhibited no significant effects on HDL levels. The study reported that the effects of probiotics on decreasing TC and LDL levels were greater in younger patients (age < 50 years) and in single-strain probiotics, mainly Lactobacillus plantarum, whereas a mixture of L. acidophilus and Bifidobacterium spp. showed no significant beneficial effects. Notably, 83.9% of the participants in our study were aged ≥ 50 years, and our probiotic mixture did not contain this strain. Furthermore, compared with the consumption of probiotic capsules, the consumption of probiotics in fermented milk products resulted in a more significant reduction in LDL levels [33]. Consistent with our findings, the two aforementioned meta-analyses did not demonstrate significant changes in the TG levels [31, 32].
In agreement with our study, the meta-analysis by Rittiphairoj et al. stated that probiotics reduced FBG more than the placebo or no-intervention groups and that there was some evidence of a reduction in HbA1c levels in the probiotic group, although this did not reach statistical significance. Their subgroup analysis found that the reduction in FBG levels was more pronounced in participants with FBG levels > 130 mg/dL than in their counterparts [34]. Notably, 60% of our participants had FBS levels ≤ 130 mg/dL, which may explain the non-significant reduction within the group and the significant reduction between the groups in our analysis. Another meta-analysis involving 237 and 235 participants in the treatment (probiotic yoghurt) and control (mostly conventional yoghurt) groups, respectively, found no effects of probiotic yoghurt on FBG and HbA1c levels in T2DM [35].
Razmpoosh et al. demonstrated a significant increase in the levels of HDL in the probiotic group, but no significant alterations were observed in TG and TC levels. They also observed a significant decrease in fasting plasma glucose (FPG) levels, consistent with our findings. However, they found no significant changes in anthropometric measurements, including weight, WC, and BMI [36]. Importantly, their study lasted for only 6 weeks, and they used Familact probiotics, which had different combinations and doses of probiotic strains than the probiotics we used.
Khalili et al. found that a daily capsule containing a minimum of 108 CFU of L. casei 01 for 8 weeks significantly decreased weight, BMI, WC, and FBS levels in the intervention group compared with the placebo group. These findings are in line with our results, despite the differences in supplementation [37]. A meta-analysis revealed that probiotic intake resulted in a significant improvement in serum levels of FBS and a non-significant improvement in HbA1c levels [38], which is congruent with our study.
Another meta-analysis included 13 randomised controlled trials involving 818 participants in eight countries in 2020. It revealed that participants who received multiple species of probiotics had a statistically significant reduction in FBS and TG levels. No significant differences were observed in HbA1c, LDL, HDL, and TC levels between the probiotic and control groups [39]. Subgroup analysis revealed that the effect of probiotic supplementation on TG was significant when participants’ ages were ≤ 55 years and revealed that participants coming from eastern regions had higher HDL concentrations than those from the western regions after probiotic supplementation [39].
In 2016, Firouzi et al. examined the effects of multistrain probiotics in 136 Malaysian adults with T2DM. Sixty-eight participants consumed a probiotic powder sachet containing six viable strains (L. acidophilus, L. casei, Lactococcus lactis, Bifidobacterium bifidum, B. longum, and Bifidobacterium infantis) at a twice-daily dose of 30 billion CFUs. In contrast, the other 68 participants in the control group consumed a placebo powder sachet for 12 weeks. However, the patients were required to follow a prescribed diet, which may not reflect real-life consumption. They found that the HbA1c level decreased by 0.14% in the probiotic group and increased by 0.02% in the placebo group in the per-protocol analysis, whereas these changes were not significant in the intention-to-treat analysis [40]. This finding partly agrees with ours, as the HbA1c level decreased by 0.38 from the mean in the probiotic group and increased by 0.26 from the mean in the placebo group; however, these changes were only significant in the placebo group.
They also reported that the participants in the probiotic group experienced a decline in FPG levels, whereas those in the control group experienced an increase in FPG levels from baseline. However, these findings were not statistically significant, consistent with the within-group analysis [38]. Conversely, Asemi et al. found that both the probiotic and placebo groups experienced increased FPG levels from baseline [41].
Limitations of studyThe dosage of FOS in the symbiotic supplement was not known in the intervention group.
This study was self-funded, limiting our ability to recruit a larger sample size or extend the study duration beyond 12 weeks.
Furthermore, this study was conducted in only two teaching hospitals on one side of Baghdad, potentially limiting the generalisability of the results.
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