Background: The efficacy of increasing dietary fiber intake (DFI) to ameliorate glycemic control in patients with type 2 diabetes (T2D) is still controversial. In this randomized open-label comparator-controlled study we tested the effect of high-fiber diet and fiber supplement on glycemic control in patients with T2D on metformin monotherapy.

Methods: Seventy-eight T2D overweight patients on metformin monotherapy were randomized 1:2:1 to 12 weeks intensive nutrition program to follow high-fiber diet (HFD), dietary fiber supplementation (FS) or standard diet recommendations (SDR). Dietary recommendations were reinforced in all groups every 4 weeks by study dieticians. Biochemistry, anthropometric measures, food frequency questionnaires to asses DFI were collected at baseline and after 12 weeks.

Results: At baseline groups did not differ in terms of mean age, BMI, metformin intake, HbA1c, fiber and calorie intake (p>0.05 for all). After three months, DFI significantly increase in both HDF and FS group but not in SDR group (HFD: 19.8 ± 6.1 g vs. 24.3 ± 6.8 g, p= 0.0001; FS: 17.5 ± 5.9 g vs. 27.0 ± 6.2 g p< 0.0001; SDR: 22.8 ± 9.1 g vs. 21.2 ± 6.4 g, p= 0.32). HbA1c significantly improved in all groups (HFD: 7.1 ± 0.5 % vs. 6.6 ± 0.6 %, p< 0.0001; FS: 7.1 ± 0.5 % vs. 6.8 ± 0.5 % p< 0.001; SDR: 7.2 ± 0.4 % vs. 6.7 ± 0.5 g, p< 0.001). All HFD, FS and SDR intervention reduced mean body weight by 2.1 ± 2.6 Kg (p< 0.0001), 1.0 ± 1.8 Kg (p< 0.05) and 1.1 ± 2.1 Kg (p< 0.05), respectively. Changes in HbA1c and body weight did not differ among groups. A significant correlation between calorie intake and the reduction of HbA1c levels was seen across groups (r= 0.307 p<0.01). No significant correlation between DFI and HbA1c levels was observed.

Conclusions: Intensive nutrition education programs with monthly meetings similarly reduced HbA1c in all groups. Furthermore, our study suggested that rather than fiber intake, caloric restriction followed by moderate weight loss is the main driver for glycemic improvement in overweight patients with T2D.


F. Tramontana: None. E. Maddaloni: Consultant; Self; Merck KGaA. Speaker’s Bureau; Self; Abbott, AstraZeneca, Pikdare. S. Greci: None. G. Defeudis: None. R. Strollo: None. P. Pozzilli: Advisory Panel; Self; Abbott, AstraZeneca, Eli Lilly and Company. Research Support; Self; Medtronic, Sanofi. N. Napoli: None.

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