Intermittent fasting linked to 135% higher death risk: Weight loss diet carries unexpected heart threat

Intermittent fasting has long been promoted as a simple way to improve health by restricting eating hours rather than calories. Tech leaders, celebrities and even political figures have publicly endorsed it, crediting the approach for weight control and better energy levels. But a new study suggests that eating within an extreme eight-hour window each day may carry serious risks for the heart.

Findings from long-term research

According to research published in Diabetes & Metabolic Syndrome: Clinical Research and Reviews and also reported in ScienceDirect, scientists tracked the eating habits of more than 19,000 American adults using data from the National Health and Nutrition Examination Survey (NHANES) between 2003 and 2018. Participants were followed for a median of eight years, during which their mortality status was monitored.

The results revealed that people who confined eating to fewer than eight hours daily had a 135% higher risk of dying from cardiovascular disease compared with those who spread meals over 12–14 hours. This increased risk remained consistent across age, sex, race, socioeconomic background and lifestyle factors, and was particularly pronounced among smokers, individuals with diabetes and those with existing heart disease.

Lead researcher Professor Victor Wenze Zhong, from Shanghai Jiao Tong University School of Medicine, noted that while short-term studies often suggested cardiovascular benefits, this longer-term data shows a more troubling picture. He explained that the findings highlight the need for personalised dietary recommendations rather than one-size-fits-all approaches.

Limitations of the study

Experts caution that the study was observational, meaning it identifies associations but does not prove causation. As Dr. Sudhir Kumar, a neurologist trained at CMC Vellore, pointed out, factors such as underlying illness or inaccuracies in self-reported diets could partly explain the outcome. People who are already unwell, for instance, may naturally eat less, which could influence the results.

Still, researchers conducted multiple sensitivity analyses, and the link between short eating windows and higher cardiovascular mortality remained robust. Interestingly, the study found no consistent link between intermittent fasting and overall mortality or cancer deaths.

Mixed evidence on health benefits

Other experts, including endocrinologist Dr. Anoop Misra, have underlined that intermittent fasting can still offer benefits such as weight loss, improved insulin sensitivity, lower blood pressure and reduced inflammation. However, he also warned of drawbacks, including nutrient deficiencies, hunger, irritability, and potential risks for older adults or those with chronic illnesses.

Previous studies add to the cautionary picture. A 2020 trial published in JAMA Internal Medicine showed only modest weight loss from intermittent fasting, with much of the reduction coming from muscle mass. Side effects such as headaches, fatigue and difficulty concentrating were also reported in other research.

A call for moderation

While the latest findings do not suggest abandoning intermittent fasting entirely, they raise important questions about its long-term safety, especially for vulnerable groups. Experts recommend more moderate eating windows, such as 10–12 hours, which may balance potential benefits with lower health risks.

For now, researchers stress that focusing on what is eaten may be more important than strictly limiting when food is consumed. Until more conclusive evidence is available, the safest approach may be moderation rather than extreme fasting schedules.