Table 2.
The description and characteristics of included studies.
| Citation/Country of Study | Study Type | Sample Details | Mean Age (Years) | Aim | Interventions | Results |
|---|---|---|---|---|---|---|
| Birkeland et al. [29]. Norway | Randomised, placebo controlled, double-blind, cross-over study | n = 25 | 63.1 (41–73) | To evaluate the prebiotic effect of inulin-type fructans on faecal microbiota and SCFA in patients with T2D. | Inulin-type fructans (a mixture of oligofructose and inulin) versus placebo (maltodextrin). A 4-week washout separated the 6 weeks of treatment. |
A daily supplement of inulin-type fructans induced a moderate, but significant increase in faecal levels of bifidobacteria, total SCFA, acetic acid and propionic acid in patients with T2D. |
| Candela et al. [26]. Italy | Open-label randomised controlled trial | Ma-Pi 2 diet: n = 21; Control diet: n = 19. |
66 | To explore the potential of two different energy-restricted dietary approaches—the fibre-rich macrobiotic Ma-Pi 2 diet or a control diet recommended by Italian professional societies for T2D treatment—to correct gut microbiota dysbiosis in T2D patients. | Fibre-rich macrobiotic Ma-Pi 2 diet versus control diet. 21 days of treatment. |
The Ma-Pi 2 diet was associated with a greater reduction in FBG. Body weight changes (mean ± SD) kg: Ma-Pi 2 diet: −5.6 ± −1.0 Control diet: −2.7 ± −0.6 |
| Gonai et al. [30]. Japan | Randomized controlled, double-blind study | GOS: n = 27; Placebo: n = 25. |
GOS: 55 ± 11 Placebo: 54 ± 12. |
To assess the effects of GOS on glycaemic control and gut microbiotas and metabolites in patients with T2D. | Galacto-oligosaccharide (GOS) versus placebo (maltodextrin). Four weeks of treatment. | GOS restored the abundance of Bifidobacteriaceae. However, GOS did not have a significant effect on glucose tolerance. |
| Medina-Vera et al. [22]. Mexico | Single-centre, placebo-controlled, randomised double-blind | T2D: n = 81 (randomised: 9 subjects from each group discontinued study) final group numbers analysed: DF: n = 28 Placebo: n = 25 |
DP: 50.4 ± 8.7 Placebo: 49.8 ± 10.6 |
To study the effects of a functional food-based dietary intervention on faecal microbiota and biochemical parameters in patients with T2D. | A dietary portfolio (DP) versus placebo. A 3-month treatment period. |
DP consumption stimulated the abundance of Bifidobacterium longum shown to improve insulin sensitivity. There were no significant differences in the levels of glucose between groups. Patients with T2D following the DP showed significant reductions in specific biochemical parameters compared with the placebo group: AUCs for glucose. |
| Pedersen et al. [23]. UK |
Randomised, double-blind, placebo-controlled parallel study | GOS: n = 14; Placebo: n = 15. | GOS: 56.7 ± 1.6; Placebo: 58.1 ± 1.7. |
To compare the effects of prebiotic supplementation with placebo treatment for 12 weeks on glucose control, intestinal permeability, intestinal bacterial composition, and endotoxaemia in patients with T2D. | Galacto-oligosaccharide (GOS) versus placebo (maltodextrin): 12 weeks of treatment. |
Prebiotic fibre supplementation had no significant effects on clinical outcomes or bacterial abundances compared with placebo. Body weight changes (mean ± SEM) kg: GOS: 0.6 ± 0.1 Placebo: 0.1 ± 0 |
| Reimer et al. [31]. Canada |
Placebo-controlled, double-blind, randomised controlled study | PGX®: n = 147 Placebo: n = 143. |
PGX®: 56.2 ± 8.6 Placebo: 53.4 ± 9.9. |
To examine the adjunct effect of the soluble viscous fibre PolyGlycopleX® (PGX®) on glycaemic control in adults with T2D. | PGX® versus placebo 52 weeks of treatment. |
The butyrate producer (Roseburia) was significantly increased in the PGX® group. Adding PGX® to a weight management program for individuals with T2D provides a sustained reduction in HbA1c compared to placebo. Body weight changes: mean (95% CI) kg PGX®: −3.87 (−1.75 to −6.0) Placebo: −1.62 (0.56 to −3.80) |
| Soare et al. [27]. Italy |
Randomized controlled, open-label trial | Ma-Pi 2 diet: n = 25; Control diet: n = 26 |
Ma-Pi 2 diet: 67 ± 8.163 Control diet: 65 ± 7.284 |
To evaluate the effect of different dietary approaches—the macrobiotic Ma-Pi 2 diet compared with standard diets recommended for patients with T2D. | Fibre-rich macrobiotic Ma-Pi 2 diet versus control diet: 21 days of treatment. |
There was significantly greater reduction in fasting blood glucose, HbA1c, and insulin resistance in those patients receiving the Ma-Pi 2 diet compared with those in the control diet group. Body weight changes (mean ± SD) kg Ma-Pi 2 diet: −4.9 ± 0.4 Control diet: −3.97 ± 0.08 |
| Soare et al. [28]. Italy |
Randomized controlled, open-label trial. 6-month follow-up study |
Ma-Pi 2 diet: n = 17 Control diet: n = 23. |
Ma-Pi 2 diet: 65 ± 8.89 Control diet: 64 ± 8.15 |
To investigate whether the benefits of the original 21-day intensive dietary interventions extended beyond the original MADIAB trial duration and into everyday life. | Fibre-rich macrobiotic Ma-Pi 2 diet versus control diet: 6 months of treatment. |
The Ma-Pi diet was associated with a higher percentage reduction in HbA1c. The Ma-Pi diet resulted in greater improvement in glycaemic control. Body weight changes: median (1st–3rd quartile) kg Ma-Pi 2 diet: −1.46 (−4.59; 0.78) Control diet: 0.72 (−2.4; 3.26) |
| Zhao et al. [13]. China |
Randomized controlled trial, open-label, parallel-group study | High dietary fibre: n = 27, Control: n = 16. |
High dietary fibre: 58.4 ± 6.2. Control: 59.7 ± 6.0; |
To characterise the dynamics of the gut microbiota and its impact on glucose homeostasis in patients with T2D. | High dietary fibre versus control (usual care) | A select group of SCFA-producing strains was promoted by dietary fibres, and most other potential producers were either diminished or unchanged in patients with T2D. Body weight changes (mean ± SEM) kg: High dietary fibre: −2.99 ± −0.16 Control: −1.09 ± −0.13 |
Abbreviations: AUCs—areas under the curve; DP—dietary portfolio; FBG—fasting blood glucose; GOS—galacto-oligosaccharide; HbA1c—glycated haemoglobin; kg—kilogram; Ma-Pi 2—macrobiotic diet; PGX®—PolyGlycopleX®; T2D—type 2 diabetes; SCFAs—short-chain fatty acids.