Intermittent Fasting Under 8 Hours May Raise Heart Death Risk by 135 Percent: Study Finds
China: A new study published in Diabetes & Metabolic Syndrome: Clinical Research and Reviews has raised safety concerns over very short time-restricted eating patterns. The research, led by Victor W. Zhong and colleagues from Shanghai Jiao Tong University School of Medicine, found that consuming all meals within an eight-hour window was associated with a significantly higher risk of cardiovascular mortality compared to a standard eating duration of 12–14 hours.
"Eating duration of less than eight hours was linked to 135% higher cardiovascular mortality, but was not associated with all-cause and cancer mortality," the study stated.
The findings challenge the widely held notion that intermittent fasting and extreme time-restricted eating offer uniform health benefits. While such dietary practices have shown short-term advantages for weight loss and metabolic health in earlier trials, their long-term safety remains uncertain.
Commenting on the findings, Dr. Anoop Misra, Chairman of Fortis-C-DOC and Editor-in-Chief of the journal, stressed caution in adopting extreme fasting patterns. “This study serves as an important safety signal against the routine use of very short eating windows. Although intermittent fasting can provide modest metabolic benefits, an eating window of less than eight hours should not be considered universally safe,” Dr. Misra noted.
He explained possible biological mechanisms behind the association, including increases in LDL cholesterol, sympathetic activation, and elevated cortisol levels, which may collectively worsen cardiovascular risk. Behavioral factors such as skipping breakfast and poor diet quality could further contribute to harm.
According to Dr. Misra, clinicians should recommend a balanced and individualized approach. He suggested avoiding eating windows shorter than 8 hours, especially for those with heart disease, uncontrolled hypertension, diabetes, pregnancy, frailty, or eating disorders. If time-restricted eating is considered, a 10–12-hour window earlier in the day is preferable. Emphasizing diet quality, adequate protein, fiber-rich foods, healthy fats, and avoiding highly processed foods are also crucial. Regular monitoring of blood pressure, lipid profile, glucose, weight, and any new symptoms is advised.
He also cautioned that in regions like India, where cardiovascular risk is already high and fasting is commonly practiced without medical guidance, professional supervision is crucial. Dr. Misra called for randomized controlled trials comparing different eating windows, as well as studies evaluating effects in diverse populations, particularly in South Asia. Until then, time-restricted eating can be considered for weight and metabolic benefits, but only under medical guidance and without extreme restrictions.
"Intermittent fasting is a promising tool in our dietary arsenal and low cost and simple too, but enthusiasm should be tempered with careful risk assessment. Until more long-term data are available, especially on hard outcomes like cardiovascular events (e.g. heart attacks), intermittent fasting should be individualized and ideally supervised, particularly for people with pre-existing health conditions, and applied for short-term only.," Dr. Misra concluded.
Reference:Chen, M., Xu, L., Van Horn, L., Manson, J. E., Tucker, K. L., Du, X., Feng, N., Rong, S., & Zhong, V. W. (2025). Association of eating duration less than 8 h with all-cause, cardiovascular, and cancer mortality. Diabetes & Metabolic Syndrome: Clinical Research & Reviews, 103278. https://doi.org/10.1016/j.dsx.2025.103278
Disclaimer: This website is primarily for healthcare professionals. The content here does not replace medical advice and should not be used as medical, diagnostic, endorsement, treatment, or prescription advice. Medical science evolves rapidly, and we strive to keep our information current. If you find any discrepancies, please contact us at corrections@medicaldialogues.in. Read our Correction Policy here. Nothing here should be used as a substitute for medical advice, diagnosis, or treatment. We do not endorse any healthcare advice that contradicts a physician's guidance. Use of this site is subject to our Terms of Use, Privacy Policy, and Advertisement Policy. For more details, read our Full Disclaimer here.
NOTE: Join us in combating medical misinformation. If you encounter a questionable health, medical, or medical education claim, email us at factcheck@medicaldialogues.in for evaluation.