Popular Intermittent Fasting Diet Linked to Cardiovascular Death Risk

People who participate in an intermittent fasting diet may be more prone to a heart-related death, researchers have found.

Those who only ate within 8 hours of the day, following a time-restricted eating schedule, were 91 percent more likely to die from cardiovascular disease than those who followed a normal schedule, according to preliminary research being presented at the American Heart Association's Epidemiology and Prevention Lifestyle and Cardiometabolic Scientific Sessions 2024 in Chicago, between March 18-21.

This finding is unexpected, as intermittent fasting has been found by previous studies to improve blood pressure, blood glucose and cholesterol levels.

Intermittent fasting is an eating pattern that cycles between periods of fasting and eating. There are several methods of intermittent fasting, but the most common ones include the 16/8 method, which involves fasting for 16 hours each day and restricting your eating window to 8 hours, and the 5:2 method, which involves eating normally for five days of the week and restrict calorie intake to 500-600 calories for two non-consecutive days.

"Restricting daily eating time to a short period, such as 8 hours per day, has gained popularity in recent years as a way to lose weight and improve heart health," study author Victor Wenze Zhong, a professor of epidemiology and biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China, said in a statement. "However, the long-term health effects of time-restricted eating, including risk of death from any cause or cardiovascular disease, are unknown."

However, this research involved analyzing data from over 20,000 adults across the U.S. and found that those on the 16/8 diet increased the risk of dying from cardiovascular disease by 91 percent, compared to those with a regular non-intermittent diet.

They found that for people with existing cardiovascular disease, eating between 8 and 10 hours of the day led to a 66 percent higher risk of death from heart disease or stroke, and that time-restricted eating did not reduce the overall risk of death from any cause.

The researchers also found that people with heart disease or cancer had a higher risk of dying from cardiovascular disease and that people with cancer who ate more than 16 hours a day had a lower risk of mortality.

"We were surprised to find that people who followed an 8-hour, time-restricted eating schedule were more likely to die from cardiovascular disease. Even though this type of diet has been popular due to its potential short-term benefits, our research clearly shows that, compared with a typical eating time range of 12-16 hours per day, a shorter eating duration was not associated with living longer," Zhong said.

"It's crucial for patients, particularly those with existing heart conditions or cancer, to be aware of the association between an 8-hour eating window and increased risk of cardiovascular death. Our study's findings encourage a more cautious, personalized approach to dietary recommendations, ensuring that they are aligned with an individual's health status and the latest scientific evidence," he continued. "Although the study identified an association between an 8-hour eating window and cardiovascular death, this does not mean that time-restricted eating caused cardiovascular death."

Some limitations of this study include the fact that people self-reported their dietary schedule, meaning that this data may be impacted by a patient's memory. The analysis also didn't include factors like duration of eating, or even the cause of death.

"This report is a conference presentation and lacks the detail of a full paper to be able to assess the quality of the research. It appears to show the risk of death over a range of 1-13 years, median of 8 years, looking at how people ate on two days, which were linked to risk of cardiovascular disease and death," Duane Mellor, a registered dietitian and senior lecturer at Aston Medical School, Aston University, who wasn't involved in the study, said in a statement.

"Although a model was used to assess risk, it is unclear if it included how healthy diet pattern was or even what people ate. As the information is limited it is not clear from the available information if smoking, physical activity and alcohol were considered as variables.

"It is impossible to say if how a person restricts the time that they eat is linked to risk of health outcome as this abstract is suggesting – as it is unclear, as the data is so limited based on two days of diet recall, why they might have been restricting the time over which they ate. Some people might be doing this for health reasons, whilst others due to stressful work environments or poverty, which are both risk factors for cardiovascular death," Mellor explained.

"We need to be very careful not to generate concerning headlines and stories based on such limited information. It is perhaps what you eat and your overall lifestyle that is more important than if you ate all your food in less than 8 hours on two days in the last decade."

The researchers hope to further examine why time-restrictive dieting may impact cardiovascular outcomes. They also wish to explore whether this trend is seen worldwide.

"The results provided in this conference abstract are quite striking and suggest that those following 'time-restricted eating' could have twice the risk of cardio-vascular death. This would challenge the commonly perceived health benefit of this popular diet," Baptiste Leurent, an associate professor in medical statistics at UCL who wasn't involved in the study, said in a statement.

"The study is based on a large sample of American adults, and – judging on the limited abstract presented – appear appropriately conducted. However, the information available is very limited. The full research has not yet been published, and these results are too brief to draw any robust conclusion. For example, it is unclear if the results reported are taking into account of the underlying difference between the groups compared.

"If the people following this diet tend to be older, or at higher cardiovascular risk, then the association may not be so surprising. Conversely, if those following this diet tend to follow a healthier lifestyle, such as more physical exercise, the risk of this diet could be even higher than the observed difference in mortality," Leurent said. "We look forward to seeing the full publication of these important findings."

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