Study design
This was a randomized, open label, controlled clinical trial conducted at Faculty of Medicine Cairo University hospitals outpatient diabetes and endocrinology nutrition clinic from November 2021 to May 2024. The protocol of our study received approval from the Research and Ethics Committee for Experimental and Clinical Studies, Faculty of Pharmacy, Cairo University CL (2987) (Approval date: April 2021). Written informed consent was obtained from all participants prior to enrollment. The trial was registered at the Pan African Clinical Trial Registry (PACTR202411524439559) and conducted following the Declaration of Helsinki [13].
Participants
Eligible participants were adults aged 21 to 60 years, diagnosed with type 2 DM, and classified as obese with a body mass index (BMI) ranging from 30 to 50 kg/m². All participants had been on metformin only therapy for at least one year. Exclusion criteria included individuals undergoing insulin therapy, those receiving other antidiabetic medications (e.g., sulfonylureas, DPP-4 inhibitors, GLP-1 receptor agonists, SGLT2 inhibitors, or thiazolidinediones), or those diagnosed with type 1 diabetes. Additionally, those engaged in high-intensity endurance exercises (defined as sustained, vigorous activities exceeding 60 minutes) were excluded. Participants with significant comorbidities that could impede adherence to dietary interventions were also excluded. These comorbidities included severe cardiovascular conditions (e.g., heart failure, myocardial infarction), respiratory diseases (e.g., chronic obstructive pulmonary disease), psychiatric disorders (e.g., major depressive disorder, schizophrenia), musculoskeletal disorders (e.g., rheumatoid arthritis), individuals with chronic liver disease, severe renal impairment (GFR < 30 mL/min/1.73 m²), or thyroid disorders. Those receiving treatment with thyroxine, antithyroid medications, or immunosuppressive agents were deemed ineligible. Additional exclusion criteria included pregnancy, and alcoholism. Also, individuals unable to provide informed consent due to cognitive impairment were excluded.
Intervention and outcomes
Eligible participants (N = 125) were randomly assigned to one of two study groups using computer-generated random numbers (Research Randomizer version 4.0). Block randomization with a block size of 4 was used in a 1:1 ratio to maintain balanced group sizes [14]. Group 1 (N = 48) followed a 12-hour night intermittent fasting regimen combined with calorie restriction, while Group 2 (N = 51) followed a calorie-restricted diet only (CR) for 12 weeks. Participants in Group 1 (night IF combined with CR) adhered to a 12-hour fasting regimen, abstaining from food from 8:00 PM to 8:00 AM daily. This modification was implemented to suit cultural and practical considerations in Egypt, promoting better adherence to the intervention. During the fasting period, participants were encouraged to consume plenty of water. In Group 2 (Calorie Restriction), participants were provided with a caloric deficit diet plan designed by a nutritionist, without fasting windows. Participants in both groups followed the same macronutrient distribution: 45% carbohydrates, 20% protein, and 35% fats [15]. Caloric intake for both groups was personalized using the Mifflin-St Jeor equation, which calculates individual energy needs based on age, gender, weight, and height, and adjusts for sedentary activity levels. A standardized calorie deficit of 500 kcal was then applied to each participant’s calories to ensure consistency in energy restriction across the groups [16, 17].
The primary outcome of the study was the absolute change in glycated hemoglobin (HbA1c) levels, given its status as a clinically meaningful indicator of glycemic control in individuals with type 2 diabetes. Secondary outcomes were categorized into efficacy and safety outcomes. Efficacy outcomes included changes in body weight, insulin resistance as measured by HOMA-IR, waist and hip circumference, waist-to-hip ratio, BMI, body composition, and the percentage reduction in antidiabetic medication use. Safety outcomes were assessed by: (i) adverse events, defined as any undesirable effects attributable to dietary interventions and systematically recorded during the intervention period. These included self-reported symptoms such as headache, dizziness, fatigue, and gastrointestinal disturbances (e.g., bloating or constipation); and (ii) patient-reported hypoglycemic episodes. Reductions in medication use were quantified as a percentage decrease in the dose of diabetes-related medications. Metformin dose reduction was considered when patients exhibited improvement in glycemic control, reflected by fasting blood glucose levels below 130 mg/dL and HbA1c values under 7% at follow-up, accompanied by a reduction in body weight. Upon meeting these criteria, the treating physician exercised clinical judgment to determine the extent of dose reduction, typically between 25–50%, based on the patient’s overall glycemic status and clinical condition [18] Body weight was measured at baseline and every 2 weeks, with the percentage change in weight calculated. HbA1c levels were analyzed at baseline and after 12 weeks. Fasting blood glucose (FBS) was assessed after an overnight fast; while fasting insulin levels were measured to assess insulin sensitivity. Additionally, HOMA-IR was calculated to estimate insulin resistance using fasting glucose and insulin values. BMI, waist, and hip circumferences were recorded at baseline and every 2 weeks. Body composition was evaluated every 2 weeks using a Body Composition Analyzer that employs bioelectrical impedance analysis (BIA) to measure the body’s resistance to a low-level electrical current, allowing for the calculation of fat mass, lean mass, and total body water [19]. Safety was monitored through patient-reported side effects, particularly symptoms of hypoglycemia and headache, alongside regular evaluations, including blood glucose levels, to ensure patient safety.
Adherence to both the fasting protocol and dietary restrictions was closely monitored by the research team at the follow-up visits every 2 weeks. These visits included regular check-ins where participants discussed their progress and challenges. The research team provided feedback, motivational support, and made the necessary adjustments. During these visits, medication adjustments and any adverse events were recorded, and biometric measurements were taken to objectively assess compliance and physiological effects. Additionally, WhatsApp groups and phone calls were used to track adherence between visits.
At baseline, all participants underwent a comprehensive assessment using the Global Physical Activity Questionnaire (GPAQ) to evaluate their baseline physical activity levels [20, 21]. The Global Physical Activity Questionnaire (GPAQ), utilized to assess physical activity levels, evaluates occupational, transport-related, and recreational activities, along with sedentary behavior [20, 21]. It records moderate- and vigorous-intensity activities lasting ≥10 minutes, expressed as Metabolic Equivalent Task (MET) minutes per week (MET-min/week). Activities are standardized at 4 METs for moderate and 8 METs for vigorous intensity. Participants achieving ≥600 MET-min/week are classified as physically active, and those reaching ≥3000 MET-min/week as highly active. Those below 600 MET-min/week are deemed inactive, emphasizing the need for interventions to promote physical activity and reduce health risks [21].
Sample size calculation
A priori sample size calculation was conducted using G*Power version 3.1.9.2, with the absolute mean difference in HbA1c selected as the primary outcome measure. The effect size (d = 0.51) was calculated based on the absolute mean change in HbA1c reported from a trial by Carter et al. (Diabetes Res Clin Pract, 2019). Based on this effect size, significance level (α = 0.05), and 80% power (β = 0.20), a minimum of 98 participants was required to detect a statistically significant difference in HbA1c between the two groups. Accounting for an anticipated dropout rate of 10%, the final required sample size was increased to 108 participants to ensure adequate statistical power [22, 23].
Data analysis
All statistical analyses were performed using version 26 of the Statistical Package for the Social Sciences (SPSS) software (IBM Corp., Armonk, NY, USA). Normality testing for the data was conducted using the Shapiro-Wilk and Kolmogorov-Smirnov tests. Descriptive statistics were computed, with continuous variables presented as mean ± standard deviation (SD) for normally distributed data, and as median and interquartile range (IQR) for non-normally distributed variables. Categorical data were summarized as frequency (count) and relative frequency (percentage). Baseline and 12-week characteristics were reported as mean ± SD for continuous variables and as frequencies (percentages) for nominal variables. The final analysis followed a modified intention-to-treat (ITT) approach, including patients who attended at least the first follow-up visit. Missing data were handled using multiple imputation (MI), based on the average of five iterations.
Group comparisons for normally distributed quantitative variables were performed using an unpaired t-test, while the non-parametric Mann-Whitney test was applied to non-normally distributed data. Within-group comparisons of serial measurements were evaluated using paired t-tests or repeated measures analysis of variance (ANOVA) for normally distributed data, and the non-parametric Wilcoxon signed-rank test for non-normally distributed data. Categorical data were compared using the Chi-square (χ²) test, with the Fisher exact test used when expected frequencies were less than 5. A p-value of less than 0.05 was considered statistically significant.