Background & aims: Several studies have reported the effects of prebiotics and synbiotics supplementation in lipid profile and glucose homeostasis, however a pooled analysis of clinical trials that assessed these parameters has not been performed in overweight or obese individuals. The aim of this study was to evaluate the effects of prebiotics and synbiotics on plasma lipid profile, fasting insulin and fasting glucose in adults with overweight or obesity.
Methods: Randomized controlled trials were systematically searched before May 2014 in electronic databases and screening reference lists. Combined and stratified (diabetics and non-diabetics trials) meta-analyzes were performed.
Results: Thirteen trials, representing 513 adult participants with Body Mass Index ≥25 kg/m² were included. Prebiotic supplementation reduced plasma total cholesterol (SMD −0.25; 95% CI −0.48, −0.02) and LDL-c (SMD −0.22; 95% CI −0.44, −0.00) concentrations in overall analysis, and reduced triglycerides (SMD −0.72; 95% CI −1.20, −0.23) and increased HDL-c (SMD 0.49; 95% CI 0.01, 0.97) concentrations in diabetic trials. Synbiotic supplementation reduced plasma fasting insulin (SMD −0.39; 95% CI −0.75, −0.02) and triglycerides (SMD −0.43; 95% CI −0.70, −0.15) concentrations.
Conclusions: The improvement of the evaluated parameters supports prebiotics and synbiotics supplementation as an adjuvant therapy in obesity-related comorbidities, such as dyslipidemia and insulin resistance.
Alex’s Notes: I know, I know, the title is an eye-catcher. As the importance of the gut microbiota continues to grow, it is important that we understand what effects modulation can have. As the title implies, the focus of this meta-analysis was on randomized controlled trials utilizing prebiotic or synbiotic (prebiotics + probiotics) supplementation in persons with a BMI greater than 25 kg/m2 and between the ages of 18 and 65-years.
Fourteen studies (ten prebiotic; four synbiotic) were included in the meta-analysis, with sample sizes ranging from 10-66 persons, and follow-up lengths ranging from 4-28 weeks. Five studies were conducted in America, five in Europe, and the remainder in the Middle East. The prebiotics were mostly inulin-type fructans with doses ranging between 5.5 and 21 g per day.The synbiotics consisted of a combination of fructo-oligosaccharides (FOS) and Bifidobacterium and/or Lactobacillus and/or Streptococcus species, but the maximum dose of FOS in synbiotic trials was 2.50 grams per day and commensal bacteria doses ranged from 2.7x108 to 50x108 colony forming units per day.
In total, 513 participants were included in this study with an estimated average age under 45 years. I honestly have no idea why the researchers wouldn’t have provided a real number. There was a predominance of women (73.9%), and the average BMI was 31.2kg/m2, ranging between 27.2 and 39.2kg/m2.
Did the fiber work?
Sure did, somewhat. Prebiotic supplementation resulted in a significant reduction in total cholesterol (-25%) and LDL-C (-22%) across the board relative to placebo, and also demonstrated efficiency in reducing triglycerides (-72%) and increasing HDL-C (49%) in diabetic persons. Effects on fasting insulin and fasting glucose were non-significant. Synbiotic supplementation only demonstrated a significant overall reduction in triglycerides (-43%) and fasting insulin (-39%) relative to placebo. Three trials reported adverse effects after prebiotic supplementation (diarrhea, constipation, bloating, flatulence, and abdominal pain).
Regarding HDL-C, the lack of effect in non-diabetic persons could have been owed to the fact that they had regular plasma HDL-c concentrations at baseline, while the diabetics had HDL-C levels below 40 mg/dL. Even without the significant effects, however, seven of the ten prebiotic trials showed a mild increase in HDL-C with intervention, which when taken in conjunction with the significant effects of prebiotics on lowering total and LDL cholesterol, definitely suggests that future investigation is warranted.
On a similar note, despite various health conditions in the included trials, the average fasting insulin levels were <20 μUI/mL at baseline, which may have prevented an important effect with prebiotic supplementation. Yet, synbiotic trials did show a significant effect, suggesting that it may indeed be the type of bacteria in the gut that play a role rather than the fiber, per se. The lack of effects on most lipid parameters in the synbiotic trials could be due to the low amount of fiber utilized (max of 2.5g). Given that soluble prebiotic fibers work through viscosity and fermentation, the dose definitely plays a role in mediating the observed effects. Regarding adverse effects, these mechanisms of action also explain the bloating and gas.
If you are overweight or obese, adding some fiber to your diet may be worth a shot. The effects will be more pronounced if you are also diabetic. Yet, keep in mind that this meta-analysis could not account for the diets of the subjects, and the effects of fiber supplementation likely depend on how much fiber is already in your diet and what your gut microbe composition looks like. Given the vast benefits of compounds other than fiber that exist within the foods that are most fibrous (i.e. vegetables, oats, etc.), it may be prudent to simply adopt a healthier “fiber-oriented” diet rather than pop some FOS pills. Oh, and don’t forget to exercise as that will definitely help with weight-loss and overall health as well.