New Study Raises Concerns Over Intermittent Fasting and Heart Health Risks
August 31, 2025 – A recent study has sparked debate in the health community by suggesting a potential link between intermittent fasting, specifically time-restricted eating, and an increased risk of cardiovascular death. Presented at an American Heart Association (AHA) conference and published in the peer-reviewed journal Diabetes & Metabolic Syndrome: Clinical Research and Reviews, the research challenges the popular perception of intermittent fasting as a universally beneficial dietary practice.
Study Findings
The study, conducted by researchers from Shanghai Jiao Tong University School of Medicine in China, analyzed data from over 19,000 U.S. adults collected through the National Health and Nutrition Examination Survey (NHANES) between 2003 and 2018. Participants, with an average age of 49, were followed for a median of eight years. The findings revealed that individuals who restricted their eating to an eight-hour window daily—a common form of intermittent fasting known as the 16:8 method—faced a 91% to 135% higher risk of dying from cardiovascular disease compared to those who ate over a 12- to 16-hour period. The risk was particularly pronounced among those with pre-existing heart disease or diabetes.
Dr. Victor Wenze Zhong, the lead author and an epidemiologist at Shanghai Jiao Tong University, emphasized that the study does not prove causation but highlights a significant association. "Our findings encourage a more cautious, personalized approach to dietary recommendations, especially for individuals with existing heart conditions," Zhong stated.
Intermittent Fasting: Benefits and Risks
Intermittent fasting, particularly time-restricted eating, has gained popularity for its potential to promote weight loss, improve insulin sensitivity, and lower blood pressure and cholesterol levels, as supported by short-term studies lasting a few months to a year. However, the new research suggests that long-term adherence to an eight-hour eating window may pose risks, including:
- Loss of Lean Muscle Mass: The study found that participants following a 16:8 fasting schedule had less lean muscle mass, which is critical for metabolic health and protecting against heart disease. A 2020 study in JAMA Internal Medicine also noted muscle loss in intermittent fasting participants.
- Circadian Misalignment: Eating at unusual times may disrupt the body’s internal clocks, potentially affecting cardiovascular health.
- Poor Dietary Choices: Some participants may engage in "reward-based eating" during restricted windows, opting for less nutritious foods, which could negate potential benefits.
Dr. Anoop Misra, a leading endocrinologist, noted in an editorial that while intermittent fasting can offer metabolic benefits, it may also lead to nutrient deficiencies, increased cholesterol, and side effects like hunger, irritability, and difficulty concentrating.
Expert Reactions and Limitations
The study has drawn mixed reactions from experts. Dr. Christopher Gardner, director of nutrition studies at Stanford Prevention Research Center, urged "healthy skepticism," pointing out that the observational nature of the study limits its ability to establish causation. He noted that the group following an eight-hour eating window included a higher percentage of men, smokers, and individuals with higher BMI, which could contribute to the elevated risk.
Additionally, the study relied on self-reported dietary data from two 24-hour recall questionnaires, which may not accurately reflect long-term eating habits. Critics, including Dr. Jason Fung, a nephrologist and intermittent fasting advocate, argue that the study’s reliance on limited data and lack of dietary quality analysis weakens its conclusions. Fung compared the findings to the flawed correlation between ice cream consumption and drowning, emphasizing that correlation does not imply causation.
Dr. Pam Taub, a cardiologist at the University of California, San Diego, expressed concern that the study’s preliminary findings, widely publicized before peer-reviewed publication, have caused confusion among her patients who have benefited from intermittent fasting, such as improved cholesterol levels.
Implications for Public Health
The study underscores the need for personalized dietary advice, particularly for individuals with heart disease, diabetes, or other chronic conditions. Dr. Zhong advised clinicians and the public to prioritize the quality of food consumed over strict adherence to eating schedules. "Focusing on what people eat appears to be more important than when they eat," he said.
Experts like Victoria Taylor, a senior dietitian at the British Heart Foundation, caution that more research is needed to understand the long-term effects of intermittent fasting. Randomized controlled trials (RCTs) over extended periods are necessary to confirm whether time-restricted eating directly impacts cardiovascular health.
Recommendations
For those considering intermittent fasting, experts recommend consulting a healthcare professional to tailor the approach to individual health needs. Alternatives like the 5:2 diet (eating normally five days a week and restricting calories on two days) or less restrictive eating windows (e.g., 12:12) may offer benefits with potentially lower risks. Maintaining a balanced diet rich in nutrients and regular physical activity remains crucial for heart health.
As the debate continues, the study serves as a reminder that dietary trends require rigorous scrutiny. Until more definitive evidence emerges, individuals are encouraged to approach intermittent fasting with caution and focus on sustainable, heart-healthy eating habits.
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