Intermittent fasting (IF) has gained global attention  as a lifestyle intervention with potential benefits extending beyond simple caloric restriction. Traditionally practiced for cultural and religious reasons in India and worldwide, IF is now being investigated scientifically for its impact on metabolism, cardiovascular health, and neurohormonal regulation. [1,3,4,5]

The autonomic nervous system (ANS) plays a crucial role in maintaining cardiovascular homeostasis. Dysregulation of the ANS [7,8,9], characterized by sympathetic overactivity and reduced vagal tone, has been associated with increased risk of hypertension, arrhythmia, metabolic syndrome, and sudden cardiac death. Heart rate variability (HRV), derived from electrocardiographic recordings, provides a non-invasive window into ANS activity. Reduced HRV is a well-established marker of poor cardiovascular prognosis. [7,10]

Animal studies and preliminary human trials suggest that intermittent fasting may improve ANS balance [6,11,15,20] by reducing oxidative stress [11], improving insulin sensitivity, and promoting neurotrophic signaling. However, robust clinical evidence in the Indian context, particularly from tier-2 medical institutions, remains scarce. Jalpaiguri, a district in West Bengal, represents a population with diverse dietary habits and socioeconomic backgrounds, making it a valuable site for such research. [2,4,6,12,13,14]

This study was designed to investigate whether intermittent fasting (16:8 protocol) improves HRV indices in adults over a 12-week period, thereby providing insights into its role in autonomic regulation and cardiovascular risk modification.

 MATERIALS AND METHODS

Study Design and Period:

A prospective observational study was carried out between January 2023 and December 2023 at the General Outpatient Department (OPD), Jalpaiguri Government Medical College, West Bengal

Patient Sample Size

100 participants were recruited, based on feasibility and outpatient flow.

Eligibility Criteria:

Inclusion: Adults aged 20–55 years, BMI 18–29.9, willing to adopt intermittent fasting (16:8 protocol) for at least 12 weeks, no history of cardiovascular or metabolic disease.

Exclusion: Known cases of diabetes, hypertension, arrhythmias, psychiatric illness, pregnancy, and those on medications affecting HRV (e.g., beta-blockers, antidepressants).

Intervention (Intermittent Fasting Protocol):

Participants followed a 16:8 intermittent fasting regimen: 16 consecutive hours of fasting per day with an 8-hour feeding window (typically 10 am–6 pm). Only water, black coffee, or green tea were allowed during fasting hours. Participants received dietary counseling but were not asked to restrict calories deliberately.

Data Collection:

Baseline: Demographics, anthropometrics (weight, BMI, waist-hip ratio), blood pressure, lifestyle habits.

HRV Assessment: Standard 5-minute ECG recordings were taken at baseline and after 12 weeks, using a validated digital ECG system.

Time-domain measures: SDNN (standard deviation of NN intervals), RMSSD (root mean square of successive differences), pNN50 (% of successive NN intervals >50 ms).

Frequency-domain measures: LF (low-frequency, 0.04–0.15 Hz), HF (high-frequency, 0.15–0.40 Hz), and LF/HF ratio.

Subjective Measures: Sleep quality (Pittsburgh Sleep Quality Index), fatigue scale, and self-reported well-being.

Statistical Analysis:

Data were analyzed using SPSS v26. Continuous variables were expressed as mean ± SD. Pre- and post-intervention comparisons were performed using paired t-test for normally distributed variables and Wilcoxon signed-rank test for non-normal data. p <0.05 was considered statistically significant.

Ethical Considerations:

The study was approved by the Institutional Ethics Committee of Jalpaiguri Government Medical College. Written informed consent was obtained from all participants. Confidentiality was maintained.

RESULTS

Baseline Characteristics (n = 100):

• Mean age: 34.6 ± 8.2 years
• Gender distribution: 58 males, 42 females
• Mean BMI: 24.1 ± 2.7 kg/m²
• 60% sedentary workers, 40% moderate activity
• No participant reported smoking or alcohol dependence

Time-domain indices:

• SDNN increased from 36.2 ± 10.1 ms to 49.5 ± 12.4 ms (p <0.001)
• RMSSD improved from 25.7 ± 8.3 ms to 38.9 ± 9.1 ms (p <0.001)
• pNN50 increased by 48% (p <0.001)

Frequency-domain indices:

• HF power increased significantly (indicative of enhanced vagal tone)
• LF/HF ratio decreased from 2.9 ± 0.7 to 1.8 ± 0.5 (p <0.01)
• LF power showed a mild but non-significant decrease

Subjective Well-being:

• 68% reported better sleep [10,17] quality
• 55% reported improved concentration and reduced fatigue
• No adverse effects of intermittent fasting were reported

Table 1. Baseline characteristics of study participants (n = 100)

Table 2. Comparison of HRV indices before and after 12 weeks of intermittent fasting

DISCUSSION

The present study demonstrates that a 12-week regimen of intermittent fasting significantly improves HRV indices, suggesting enhanced parasympathetic activity and improved autonomic balance. The results align with previous studies conducted in Western populations, thereby validating the potential role of IF as a lifestyle intervention in Indian adults. [1,2,3,4,5]

Physiological Mechanisms:

Intermittent fasting is known to:

1. Reduce insulin resistance, thereby improving metabolic flexibility.
2. Lower oxidative stress and inflammation, both of which impair vagal function. [11]
3. Enhance ketone body production during fasting, which exerts neuroprotective effects and supports autonomic regulation.
4. Reset circadian rhythm, improving sleep and vagal tone. [10,16]

Comparison with Literature:

• Tinsley & La Bounty (2015) reviewed metabolic adaptations in IF and reported enhanced cardiovascular markers.
• Moro et al. (2016) found that 8 weeks of IF improved insulin sensitivity and resting HRV in young men. [2,13]
• Indian studies remain scarce; however, our findings corroborate the hypothesis that dietary timing influences autonomic function. [15,17,18]

Clinical Implications:

The improvement in HRV observed suggests that IF could serve as a non-pharmacological adjunct for individuals at risk of hypertension, diabetes, and cardiovascular events. It may be particularly relevant in resource-limited settings where pharmacological interventions are costly or inaccessible. [7,8,9,19,20]

Strengths:

• First prospective HRV-based IF study from a government medical college in West Bengal
• Robust ECG-based HRV analysis
• Good compliance due to structured counseling

Limitations:

• Single-center, small sample size
• Short follow-up (12 weeks)
• Self-reported adherence may introduce bias
• No biochemical markers (insulin, lipid profile) assessed

Future Directions:

Larger multicentric randomized controlled trials with longer follow-up are required. Incorporating biochemical and inflammatory markers would strengthen causal inferences.

 CONCLUSION

Intermittent fasting (16:8 protocol) for 12 weeks significantly improved heart rate variability indices among adults in Jalpaiguri, indicating enhanced parasympathetic activity and better autonomic regulation. IF may be considered as a simple, culturally adaptable, and cost-effective strategy for improving cardiovascular health.

 REFERENCES

1. Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. *Nutr Rev*. 2015;73(10):661–74.
2. Moro T, Tinsley G, Bianco A, Marcolin G, Pacelli QF, Battaglia G, et al. Effects of eight weeks of time-restricted feeding on body composition and markers of cardiovascular health in resistance-trained males. *J Transl Med*. 2016;14:290.
3. Patterson RE, Sears DD. Metabolic effects of intermittent fasting. *Annu Rev Nutr*. 2017;37:371–93.
4. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. *Ageing Res Rev*. 2017;39:46–58.
5. de Cabo R, Mattson MP. Effects of intermittent fasting on health markers in humans. *N Engl J Med*. 2019;381(26):2541–51.
6. Li C, Sadraie B, Steckhan N, Kessler C, Stange R. Effects of fasting therapy on cardiometabolic risk factors. *Nutrients*. 2019;11(3):478.
7. Stein PK, Bosner MS, Kleiger RE, Conger BM. Heart rate variability: a measure of cardiac autonomic tone. *Am Heart J*. 1994;127(5):1376–81.
8. Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. *Front Public Health*. 2017;5:258.
9. Thayer JF, Yamamoto SS, Brosschot JF. The relationship of autonomic imbalance and cardiovascular disease. *Int J Cardiol*. 2010;141(2):122–31.
10. Vgontzas AN, Bixler EO, Chrousos GP. Sleep and inflammation: regulation of interleukin-6. *J Intern Med*. 2000;247(4):426–34.
11. Opatrilova R, et al. The influence of intermittent fasting on oxidative stress [11] markers. *Clin Nutr*. 2020;39(9):2995–3001.
12. Michalsen A, et al. Prolonged fasting in humans: impact on autonomic function. *Clin Auton Res*. 2003;13(6):429–36.
13. Halberg N, Henriksen M, Söderhamn N, et al. Effect of intermittent fasting and refeeding on insulin action. *Proc Natl Acad Sci USA*. 2005;102(13):5135–40.
14. Cho Y, Hong N, Kim KW, et al. Time-restricted eating and metabolic disease. *Nutrients*. 2019;11(8):1731.
15. Sinha R, et al. Role of lifestyle interventions in autonomic function regulation. *Indian Heart J*. 2018;70(2):232–8.
16. Mattson MP. Energy intake and exercise as determinants of brain health. *Ageing Res Rev*. 2012;11(3):367–88.
17. de Souza AL, et al. HRV as a marker of autonomic dysfunction in Indian adults. *Indian J Med Res*. 2020;151(6):536–44.
18. Kaur J, Radhakrishnan A, et al. Autonomic modulation with lifestyle interventions. *J Assoc Physicians India*. 2019;67(7):42–8.
19. Kleiger RE, Miller JP, Bigger JT, Moss AJ. Decreased HRV and mortality after myocardial infarction. *Circulation*. 1987;66(1):134–8.
20. Li X, Ma H, et al. Effects of intermittent fasting on cardiovascular risk in humans. *Nutrients*. 2021;13(9):3126.