AimTo study the effects of a functional food-based dietary intervention on faecal microbiota and biochemical parameters in patients with type 2 diabetes (T2D). Materials and methodsThis placebo-controlled, randomized, double-blind study included 81 patients with T2D divided into two 3-month treatment groups: one following a reduced-energy diet with a dietary portfolio (DP) comprising high-fibre, polyphenol-rich and vegetable-protein functional foods; the other taking a placebo (P). The primary outcome was the effect of the DP on faecal microbiota. Secondary endpoints were biochemical parameters, lipopolysaccharide, branched-chain amino acids, trimethylamine N-oxide, glycosylated haemoglobin (HbA1c) and free fatty acids (FFAs). ResultsPatients with T2D exhibited intestinal dysbiosis characterized by an increase in Prevotella copri. Dietary intervention with functional foods significantly modified faecal microbiota compared with P by increasing alpha diversity and modifying the abundance of specific bacteria, independently of antidiabetic drugs. There was a decrease in P. copri and increases in Faecalibacterium prausnitzii and Akkermansia muciniphila, two bacterial species known to have anti-inflammatory effects. The DP group also exhibited significant reductions in areas under the curve for glucose, total and LDL cholesterol, FFAs, HbA1c (P< 0.05), triglycerides and CRP, and an increase in antioxidant activity (P< 0.01) vs. the P group. ConclusionLong-term adherence to a high-fibre, polyphenol-enriched and vegetable-protein-based diet provides benefits for the composition of faecal microbiota, and may offer potential therapies for improvement of glycaemic control, dyslipidaemia and inflammation.