Examining Intermittent Fasting: Cardiovascular Benefits and Risks Revealed

Recent research questions if intermittent fasting truly supports heart health, revealing new risks to cardiovascular longevity.

By Medha deb

Created on Sep 28, 2025

Recent research questions if intermittent fasting truly supports heart health, revealing new risks to cardiovascular longevity.

Intermittent fasting (IF)—especially the time-restricted eating (TRE) model, where eating is restricted to an 8-hour window—has garnered immense popularity for its supposed health benefits. These claims range from weight loss and improved blood sugar control to greater longevity. However, newly emerging research suggests that the relationship between IF and cardiovascular health may be more complicated than previously believed.

What Is Intermittent Fasting?

Intermittent fasting refers to eating patterns that alternate periods of fasting with periods of normal food intake. Common methods include:

Time-Restricted Eating (TRE): Eating within a specific window each day (e.g., 8 hours on, 16 hours off).
Alternate-Day Fasting (ADF): Alternating between fasting days (few or no calories) and regular eating days.
5:2 Diet: Eating normally 5 days per week, and significantly restricting calories on 2 non-consecutive days.

The Early Evidence: Potential Health Benefits of Intermittent Fasting

Previous studies have indicated several promising benefits associated with intermittent fasting, such as:

Weight loss
Improved insulin sensitivity
Lower blood pressure
Reduced inflammation
Positive changes in lipid profiles
Potential improvement in neurodegenerative disease risk, like Alzheimer’s and Parkinson’s
Possible overall increase in longevity

These findings led to significant enthusiasm among those seeking to manage obesity, metabolic diseases, and cardiovascular risk factors using diet alone.

New Research Casts Doubt: Increased Risk of Cardiovascular Death

However, a wave of recent large-scale observational studies and presentations at major medical conferences have raised critical questions about long-term cardiovascular safety of intermittent fasting, particularly time-restricted eating.

Key findings from a major U.S. study presented at the 2024 American Heart Association conference:

Researchers analyzed dietary data from more than 20,000 adults.
Participants who routinely restricted their eating to an 8-hour window per day were found to have a 91% higher risk of dying from cardiovascular disease during an average follow-up of 8 years compared to those who ate over a typical 12-16 hour period.
The increased mortality risk was especially evident in people with preexisting heart disease.
Restrictive eating windows (<8 hours) were not associated with living longer overall compared to more typical eating patterns.
People with cardiovascular disease who practiced IF had a greater than 50% higher risk of cardiovascular mortality.

This research suggests that, despite short-term benefits for weight and blood pressure, chronic use of restrictive eating windows may potentially elevate long-term cardiovascular mortality risk.

Detailed Look: Major Study and Its Implications

The American Heart Association study meticulously tracked participants’ dietary habits using national health surveys and then followed them for health outcomes over nearly a decade. Here are some essential points:

Study participants were middle-aged (average age 49).
Eating duration was recall-based, and only two 24-hour dietary recalls were used to estimate eating windows.
The risk persisted after accounting for lifestyle variables (such as physical activity, socioeconomic status, and baseline health).
No significant effect was observed on all-cause mortality or cancer-related death, but the cardiovascular death link remained strong.

Although observational, these findings challenge the popular narrative that intermittent fasting unilaterally improves heart health, demanding caution and further nuanced research.

Understanding the Conflicting Evidence: Short-Term Gains vs. Long-Term Risks

Potential Benefit	Possible Long-Term Risk
Improved weight management	Elevated risk of cardiovascular death (especially in at-risk populations)
Reduced blood pressure and inflammation	Possible adverse heart remodeling (e.g., fibrosis in experimental animals)
Enhanced metabolic markers (glucose, cholesterol)	No overall gain in lifespan demonstrated in adults
Potential for neuroprotective effects	Observational data may suffer from confounding; results need rigorous replication

Numerous human trials and meta-analyses have continued to show improvements in many cardiometabolic risk factors (weight, blood pressure, glucose), especially over the short term. However, these often do not extend to evidence of reduced overall cardiovascular events or proven increases in longevity.

Experimental data in rodents mirror some human observational concerns, with long-term fasting regimens leading to harmful cardiac changes, underscoring the need for caution.

What Explains the Unexpected Outcomes?

Why might a regimen that improves weight and blood pressure also raise heart disease mortality risk over the long term? Experts propose several possible explanations:

Selection bias: People who self-select restricted eating may differ from general population in unmeasured ways, possibly related to underlying health issues.
Nutritional deficiencies: Narrow eating windows may make it difficult to consume a balanced, nutritious diet, leading to deficiencies that harm heart health.
Stress response: Extended fasting in vulnerable individuals may increase stress hormone production or negatively impact heart rhythm and cardiovascular reserve.
Pre-existing conditions: Risks appear magnified for those with diagnosed heart disease or cancer, suggesting IF may not be universally appropriate.
Lack of diversity in study populations: Most large studies are U.S.-based and may not represent the full spectrum of dietary habits or ethnic backgrounds.

Current Expert Recommendations

Given the fast-developing research landscape, health organizations and clinicians tend to recommend an individualized approach:

IF may provide short-term benefits for weight loss and metabolic syndrome.
Those with heart disease, stroke risk, or cancer should consult their healthcare provider before attempting time-restricted eating.
Ensuring nutritional adequacy remains essential, regardless of eating window.
If considering IF, focus on overall dietary quality (adequate protein, vitamins, minerals, fiber).
Ongoing or planned randomized controlled trials may offer additional clarity about long-term impacts.

The Path Forward: What Future Research Needs to Address

Nutrition researchers emphasize several points when discussing next steps:

Long-term, randomized controlled trials are crucial to establish causality and clarify the safety of IF in all major populations.
Larger, more rigorous studies should stratify risk by baseline health status (especially for those with cardiovascular or oncologic disease).
More detailed measurement of dietary quality, meal composition, and concurrent lifestyle habits is needed.
Mechanistic investigations (e.g., hormonal, metabolic, and inflammation pathways) may explain individual variability in risk or benefit.

Frequently Asked Questions (FAQs)

Q: Is intermittent fasting safe for everyone?

A: No. While intermittent fasting shows benefit for some, new evidence reveals increased cardiovascular death risk for those with pre-existing heart disease and possibly cancer. Speak to your healthcare provider for individualized advice.

Q: Does intermittent fasting help lower heart disease risk in healthy people?

A: Evidence remains mixed. Short-term studies suggest benefits in weight, blood pressure, and inflammation, but recent long-term data indicate no reduction in lifespan and even possible harm in certain groups.

Q: Are there safer ways to use intermittent fasting?

A: If you are healthy, consider a moderate approach (e.g., 12-hour eating window). Always ensure your diet is nutrient-dense, and avoid fasting if you have heart disease unless guided by a clinician.

Q: What should people with heart disease or cancer do?

A: Avoid starting or continuing time-restricted eating regimens without consulting your medical team. Evidence indicates increased cardiovascular mortality risk in these populations.

Q: What are key signs intermittent fasting might not be right for me?

A: Persistent fatigue, dizziness, mood changes, poor nutrition, or worsening underlying conditions are all warning signals to stop and seek medical guidance.

Key Takeaways

Intermittent fasting (especially time-restricted eating) can result in short-term improvement of risk markers like weight and blood pressure.
Recent large studies suggest an elevated long-term risk of cardiovascular mortality, especially for those with pre-existing heart disease who use restrictive eating windows (less than 8 hours).
Benefits and risks may be highly individualized.
Ongoing research is needed to provide more definitive guidance, especially for vulnerable patient groups.

Talk to your physician before making significant changes to your eating patterns—especially if you have a diagnosis of heart disease, cancer, or other chronic condition.

References & Resources

Missouri Baptist Health: Intermittent Fasting and the Impact on Your Heart
Frontiers in Nutrition: A perspective on intermittent fasting and cardiovascular risk
American Heart Association: Time-restricted eating may raise cardiovascular death risk
Journal articles on network meta-analyses of fasting and cardiovascular outcomes

References

Author

medha deb

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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