Effects of time restricted feeding (16/8 protocol) on glycated hemoglobin levels in individuals with type II diabetes and obesity

Obesity is a major public health concern associated with an increased risk of type II diabetes and metabolic complications. Glycated hemoglobin (HbA1c) is the gold‑standard marker for long‑term glycemic control; reductions in HbA1c are linked to a lower incidence of micro‑ and macrovascular complications. The aim of this study was to assess the impact of a time‑restricted feeding (16/8) protocol on HbA1c levels in adults with type II diabetes and obesity. We conducted a retrospective, cross‑sectional analysis of 70 adults (BMI ≥ 30 kg/m²) enrolled in the PROIPRO 10‑0523 research project at the National University of San Luis. Participants followed a 16‑hour overnight fast (20:00–12:00) and an 8‑hour unrestricted eating window (12:00–20:00) for 12 consecutive weeks, with weekly nutritional counseling and monitoring. HbA1c was measured by HPLC before and after the intervention. Paired t‑tests assessed changes in HbA1c, and χ² tests compared the proportion of participants achieving normoglycemia (HbA1c < 5.7 %). Results showed a reduction in mean HbA1c from 7.8 ± 0.6 % to 5.9 ± 0.4 % (Δ = –1.9 points; p < 0.001; Cohen’s d = 2.78). Seventy percent of participants reached normal HbA1c values versus 0 % at baseline (χ² = 18.74; p < 0.0001). No significant sex differences were observed in the magnitude of HbA1c reduction (p = 0.39). We conclude that the 16/8 protocol, under clinical supervision and behavioral support, produced a significant and clinically meaningful decrease in HbA1c in individuals with obesity. These findings exceed those reported in prior meta‑analyses and align with early time‑restricted feeding trials in prediabetic populations. Personalized nutritional follow‑up and high adherence appear to be key factors in maximizing the benefits of intermittent fasting. Future randomized trials should include measurements of inflammatory, lipid, and oxidative‑stress markers, as well as assessments of long‑term sustainability.