Impact of Intermittent Fasting on Glycemic Control in Type 2 Diabetes: An Original Research

ABSTRACT

Background:

“Type 2 diabetes (T2D)” requires effective glycemic control to prevent complications. “Intermittent fasting (IF)” is a potential lifestyle intervention that may improve glycemic outcomes, though evidence is still evolving.

Objective:

This study evaluated the impact of IF on glycemic control and metabolic health in T2D.

Methods:

One hundred adults with T2D were randomly assigned to an IF group (50 following an 8-h eating window) or a control group, non-dietary advice. The primary outcomes were glycated Hemoglobin A1c (HbA1C), and fasting glucose; secondary outcomes included “body mass index (BMI)” or waist circumference, a surrogate marker of central obesity, and insulin resistance by homeostasis model assessment-insulin resistance test (HOMA-IR). We performed hypothesis tests to test for changes within and between groups.

Results:

The IF group showed a significant drop in HbA1c (8.2 to 7.4%, P < 0.001), fasting glucose, BMI, waist circumference, and insulin resistance index by HOMA-IR (3.8 to 3; P < 0.01).

Conclusion:

IF significantly improved glycemic control, body composition, and insulin sensitivity in T2D patients, indicating its potential as a non-pharmacological management strategy. Further research is recommended to explore long-term effects and IF regimen variations.

INTRODUCTION

Type 2 diabetes (T2D) is a major global health issue, with millions affected by its complications, including cardiovascular disease and neuropathy. Maintaining glycemic control is vital in T2D management to prevent these complications.[1] Alongside medications, lifestyle changes, particularly diet, are crucial. Recently, intermittent fasting (IF) has gained attention as a dietary strategy that may improve glycemic control and insulin sensitivity in T2D.[2,3]

IF typically alternates periods of eating with fasting, in patterns like time-restricted feeding (TRF) and alternate-day fasting. These regimens may enhance glucose and lipid metabolism by triggering metabolic changes that reduce insulin resistance, a key issue in T2D.[4,5] Studies also suggest IF reduces oxidative stress and inflammation, both linked to T2D pathogenesis.[6]

While preliminary findings are promising, research on IF in T2D remains inconclusive regarding long-term efficacy and safety. Some studies report that IF improves glycated hemoglobin (HbA1c) and fasting glucose levels, but others highlight challenges in sustaining these improvements over time.[7,8,9,10] This study investigates IF’s impact on glycemic control in T2D, hypothesizing that it offers a viable, non-pharmacological option to improve glycemic outcomes.

MATERIALS AND METHODS

The purpose of this six-month randomized controlled experiment was to evaluate how IF affected the glycemic management of patients with T2D at a tertiary care diabetes center. The Institutional Review Board provided ethical approval, and each subject gave their informed consent.

Participants

Participants were 40–65-year-old people with T2D, stable antidiabetic medication for at least six months, and HbA1c levels between 6.5% and 10%. Type 1 diabetes, advanced comorbidities (such as cardiovascular or renal disease), pregnancy, and insulin therapy were among the exclusion criteria. With an alpha level of 0.05 and a power of 80%, power analysis was used to estimate the sample size of 100 for the detection of a substantial HbA1c drop.

Intervention

Random assignment was used to place participants in either the control or the IF groups. The IF group followed a TRF schedule, which involved 16 h of fasting after eating within an 8-h window from 12 to 8 p.m. The control group continued to eat as normal.

Observations

Changes in fasting glucose and HbA1c were the main results. Insulin sensitivity (homeostasis model assessment-insulin resistance, HOMA-IR), waist circumference, and body mass index (BMI) were secondary outcomes.

Data analysis was done with IBM SPSS Statistics Version 29.0.2.0, Armonk. Within-group and between-group differences were assessed using paired and independent t-tests, with P < 0.05 designated as the statistical significance level.

RESULTS

Participant characteristics

A total of 100 participants were enrolled in the study, with 50 assigned to the IF group and 50 to the control group. The baseline characteristics were similar between groups in terms of age, HbA1c, fasting glucose, BMI, and waist circumference, as shown in Table 1.

Table 1.

Baseline characteristics of participants

Characteristic	IF	Control	P
Age (years)	56.4±6.3	55.9±5.8	0.45
HbA1c (%)	8.2±1.0	8.1±1.2	0.30
Fasting Glucose (mg/dL)	160±30	158±32	0.52
BMI (kg/m2)	28.5±3.2	28.6±3.4	0.40
Waist Circumference (cm)	96.2±5.6	95.8±5.7	0.48

IF=Intermittent fasting, HbA1c=Hemoglobin A1c, BMI=Body mass index

Primary outcomes

After six months, the IF group demonstrated a significant reduction in HbA1c levels, with a mean decrease from 8.2% ±1.0% at baseline to 7.4% ±0.8% (P < 0.001). In contrast, the control group showed a modest reduction in HbA1c from 8.1% ±1.2% to 7.9% ±1.1% (P = 0.05). Fasting blood glucose levels also decreased significantly in the IF group, from 160 ± 30 mg/dL to 130 ± 25 mg/dL (P < 0.001), while the control group had a non-significant change from 158 ± 32 mg/dL to 155 ± 28 mg/dL (P = 0.20) [Table 2].

Table 2.

Changes in primary and secondary outcomes after six months

Outcome	IF	Control	P
HbA1c (%)	7.4±0.8*	7.9±1.1	<0.001
Fasting Glucose (mg/dL)	130±25*	155±28	<0.001
BMI (kg/m2)	26.9±3.1*	28.3±3.2	<0.01
Waist Circumference (cm)	90.8±5.3*	94.5±5.4	<0.01
HOMA-IR	3.0±0.6*	3.7±0.8	<0.01

IF=Intermittent fasting, HbA1c=Hemoglobin A1c, HOMA-IR=Homeostatic model assessment for insulin resistance, BMI=Body mass index. Presented as Mean±SD; *Statistically significant change from baseline (P<0.05)

Secondary outcomes

BMI and waist circumference both showed significant reductions in the IF group. The mean BMI decreased from 28.5 ± 3.2 kg/m² to 26.9 ± 3.1 kg/m² (P < 0.01), while waist circumference decreased from 96.2 ± 5.6 cm to 90.8 ± 5.3 cm (P < 0.01). In the control group, changes in BMI and waist circumference were not statistically significant. Additionally, insulin resistance, as measured by HOMA-IR, improved significantly in the IF group, with a decrease from 3.8 ± 0.7 to 3.0 ± 0.6 (P < 0.01), compared to a non-significant change in the control group [Table 2].

DISCUSSION

This study demonstrated that IF significantly improved glycemic control in patients with T2D as shown by reductions in HbA1c, fasting glucose levels, BMI waist circumference, and insulin resistance (HOMA-IR). These results indicate IF’s potential as a non-pharmacological approach for T2D management, supporting research that highlights structured fasting patterns’ benefits for metabolic health.[1,2]

Comparison with existing literature

Our findings align with prior studies showing IF’s positive impact on glucose and insulin regulation in T2D. A study by Arnason et al. (2020)[3] found that TRF significantly reduced HbA1c and fasting glucose, similar to our results. Likewise, animal studies and smaller clinical trials suggest fasting periods improve insulin sensitivity and reduce oxidative stress, both linked to T2D pathogenesis.[4] However, improvements in glycemic markers like HbA1c have varied across studies due to differences in fasting regimens, intervention duration, and patient characteristics.[5]

Mechanistic insights

The observed benefits in glycemic control may stem from metabolic changes induced by fasting. Glycogen depletion during fasting encourages lipid oxidation, elevating free fatty acids, which in turn enhances insulin sensitivity.[6] Fasting also promotes autophagy and lowers oxidative stress, reducing inflammation that contributes to insulin resistance.[7,8,9,10] These physiological shifts may explain the improvements in fasting glucose, BMI, and waist circumference observed in the IF group.

Limitations and strengths

While encouraging, our study has limitations. The six-month duration may not fully capture IF’s long-term safety or sustainability in T2D. Self-reported adherence introduces potential bias, and using a single IF regimen limits generalizability. However, the randomized controlled design and detailed metabolic measures strengthen its contributions to understanding IF’s effects on glycemic control.

Future directions

Further studies should explore IF’s long-term effects, diverse fasting patterns, and impacts on diabetes complications to refine IF as a therapeutic strategy. Research into IF’s psychological impact and patient adherence over time will also inform its viability as a long-term option for diabetes care.

CONCLUSION

In conclusion, this study provides evidence that IF may offer a beneficial dietary strategy to improve glycemic control in T2D patients. IF has the potential to be incorporated into diabetes care as a lifestyle intervention, pending further validation in larger, longer-term studies.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.