Table 6.

Human intervention studies.

Authors	Trial	Population	Administration	Duration	Intervention	Results
[84]	Double-blinded, placebo-controlled, randomized clinical trial	n: 45 (25 M/20 W) 35–75 yr (median age 66 yr) n: 30 Mild to moderate Parkinson’s disease + dysbiotic fecal microbiota	Colonic single-dose anaerobically prepared FMT. FMT via colonoscopy	48 weeks	Single-dose FMT via colonoscopy (n: 30) Single-dose placebo via colonoscopy (n: 15)	FMT was linked to mostly transient gastrointestinal adverse events without clinically meaningful improvements. Stronger increase in dopaminergic medication and improvement in certain motor and non-motor outcomes in the placebo group.
[81]	12-week randomized, double-blinded, placebo-controlled clinical trial	n: 60 (50–90 yr) Parkinson’s disease	Probiotic administration via capsule ingestion	12 weeks	Capsule: 8 × 109 CFU/day probiotic (Lactobacillus acidophilus, Bifidobacterium bifidum, Lactobacillus reuteri, and Lactobacillus fermentum, each 2 × 109 CFU/g) (n: 30; 67.7 yr) Placebo (n: 30; 68.2 yr)	Decreased MDS-UPDRS. Reduced high-sensitivity C-reactive protein and malondialdehyde and enhanced glutathione levels. Reduction in insulin levels and insulin resistance.
[80]	Single-arm, Mediterranean diet intervention study (PREDIMED trial protocol)	n: 8 Parkinson’s disease	Mediterranean diet	5 weeks	Mediterranean diet intervention. Olive oil; ≥2 daily servings of vegetables; ≥2–3 daily serving of fresh fruits; ≥3 weekly servings of legumes; ≥3 weekly servings of fish or seafood; ≥3 weekly servings of nuts or seeds; white meats; and cook at least twice a week with a sofrito sauce. Ad libitum: nuts, eggs, fish, seafood, low-fat cheese, and whole-grain cereals.	Constipation syndrome scores decreased. Modified gut microbiota: Bilophila slightly decreased, Roseburia significantly lowered. No differences in markers of intestinal permeability.
[82]	Double-blinded on the day of the procedure and unblinded at the time of data analysis	n: 6 3 M, 47–73 yr, median age 52 yr 3 W, 52–71 yr, median age 64 yr Parkinson’s disease and constipation	FMT infused via colonoscopy	24 weeks	300 mL of fecal suspension of donor stool delivered in three portions: 100 mL at the terminal ileum, 100 mL at the cecum, and 100 mL along the rest of the colon	Improvement in PD motor and non-motor symptoms, including constipation, at 6 months.
[83]	Randomized, placebo-controlled trial	n: 54 30–85 yr Mild to moderate Parkinson’s disease	Fecal microbiota transplantation via capsule ingestion	12 weeks	FMT capsule (n: 27; 15 M, 12 W, median age 60.5 yr) Placebo (n: 27; 17 M, 10 W, median age 62.6 yr)	Significant improvement in PD-related autonomic symptoms (MDS-UPDRS total score). Improved gastrointestinal disorders and a marked increase in the complexity of the microecological system.