Experts Question Study Linking Intermittent Fasting to Increased Risk of Cardiovascular Death

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An observational study in China linked eight-hour, time-restricted eating to a 91 percent higher risk of cardiovascular death, yet experts say not so fast.

Researchers from Shanghai Jiao Tong University School of Medicine in China presented findings at a recent American Heart Association (AHA) meeting in Chicago questioning the safety of time-restricted eating (TRE), a type of intermittent fasting that has recently gained popularity.

The observational study of over 20,000 U.S. adults found that those who limited their eating to less than eight hours per day had a 91 percent higher risk of cardiovascular death compared with those who ate for 12 to 16 hours per day. The results from the study were presented in March at the AHA’s Lifestyle Scientific Sessions meeting. Still, the AHA has only published the study’s abstract, a precursor to a study that only briefly describes its findings. With minimal information, many health experts are speculating about the exact details of the study protocol and its results.

Dr. Sanjay Bhojraj, a board-certified cardiologist, told The Epoch Times in an email, “Although the headlines from this abstract are grabbing attention, the actual information from this study is quite limited.”

Potential Benefits of Intermittent Fasting

Intermittent fasting (IF), an eating pattern that cycles between periods of eating and fasting, has become a popular way to lose weight and improve overall health. Michelle Routhenstein, a cardiology dietitian and certified diabetes educator, told The Epoch Times in an email, “Intermittent fasting involves abstaining from food intake for specific durations, ranging from a 16-hour fasting period with an 8-hour eating window, as demonstrated in this study, to a 12-hour fasting period followed by a 12-hour eating window, or even a 22-hour fasting period with a 2-hour eating window.”

According to Ms. Routhenstein, intermittent fasting offers potential benefits for weight management. Still, the timing of these intervals varies, and the eating window may play an essential role in influencing heart health outcomes.

Dr. Bhojraj is an avid proponent of intermittent fasting. “Honestly, when IF and TRE were first introduced, I thought it was kind of ridiculous. I remember thinking, ‘Skip breakfast, and that’s supposed to be healthy?’ I’ve been doing TRE for years now and I use it as one of the pillars of my online cardiometabolic optimization program, called Well12. TRE is free, effective, and approachable for most people,” he said.

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Few studies have investigated the long-term effects of intermittent fasting. Victor Wenze Zhong, the senior study author and chair of the Department of Epidemiology and Biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China, said in an AHA press release, “The long-term health effects of time-restricted eating, including the risk of death from any cause or cardiovascular disease, are unknown.”

91 Percent Higher Risk of Death, but Comorbidities Not Considered

The overall structure of the study’s research protocol is essential to understand when considering results since this was an observational study in which researchers collected participant information without assigning them an intervention. In this case, the participants weren’t assigned intermittent fasting; they were already doing it. The researchers simply gathered information and tracked participants over time.

According to Ms. Routhenstein, “The study utilized a large sample size and adopted a longitudinal design, spanning an average of 8 years to observe individuals. The dietary information was gathered through two 24-hour recalls, which may limit the accuracy of the study findings as dietary patterns can vary over time.”

Participants answered questions about their dietary patterns for the annual 2003–2018 National Health and Nutrition Examination Survey (NHANES). The survey was given to participants one to two times during the first year of the study, and participants were then tracked for 15 years to measure the impact on their long-term health.
According to the study’s abstract poster presentation, among the over 20,000 participants, only 414 were in the eight-hour or TRE feeding arm, where they ate all their calories within eight hours. The number of participants who ate within a 12- to 16-hour window was 11,831. Additionally, 27.1 percent of the 414 TRE study participants were current smokers, a significantly higher percentage than 16.9 percent of smokers in the 12- to 16-hour window. The group in the eight-hour window also reported the highest body mass index (BMI)—29.9 percent compared to a BMI of 28.5 percent in the 12- to 16-hour window group.

The poster presentation also shows that of the 414 participants in the eight-hour window, 85 (20 percent) died compared to only 12.5 percent who died in the 12- to 16-hour study window.

Unfortunately, the study didn’t consider other comorbidities, lifestyle habits, or diet to determine the cause of death other than the difference in meal timing.

In an AHA press release, Mr. Zhong said, “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.”

The analysis found the following:

  • Participants who routinely ate all of their food within an eight-hour time frame each day had a 91 percent higher risk of death due to cardiovascular disease.
  • People living with heart disease or cancer also showed an increased risk of cardiovascular death.
  • Among participants with existing cardiovascular disease, an eating duration of eight to 10 hours per day was also associated with a 66 percent higher risk of death from heart disease or stroke.
  • The overall risk of death from any cause was not reduced with time-restricted eating.
  • Researchers found an association between an eating duration of more than 16 hours per day and a lower risk of cancer mortality among people with cancer.

Researchers stated that some aspects of the study were limiting.

Study Limitations

Study limitations include the reliance on self-reported dietary data, which depend on participant memory and recall and may not be accurate. Besides daily eating duration, other factors that could have caused death were not included in the analysis.

The researchers took the information from participants as far back as 2003. Although time-restricted eating and intermittent fasting are well-known concepts today and practiced by many to benefit health, it is questionable whether the study participants in the earlier years consciously practiced intermittent fasting with their health in mind.

According to Dr. Bhojraj, time-restricted eating wasn’t mainstream in 2003 when the study began. “I first became aware of intermittent fasting around 2015 or so. That was when the biohackers first started preaching IF. After that, the usable scientific data started coming out about the benefit for autophagy (self-healing) and particularly in metabolic diseases, which is my area of interest as a cardiologist,” he said.

Dr. Bhojraj pointed to other problems with the study, including the fact that the evidence is only included in the brief abstract, the complete research study is not available for review, and the evidence still needs to be peer-reviewed. “We have no idea about the integrity of the data,” he said. “Unfortunately, when we are dealing with research outside of the U.S., particularly from China, we have to be cautious about the integrity of the data.”

There’s also a need for the participants’ health histories, Dr. Bhojraj said. “We have no idea about the medical comorbidities in these patients. For example, were they diabetic? Did they have known heart disease?

“It is poor science to make this claim based on two days of eating patterns. A more valid study would have research participants log their data for years to ensure they were adhering to their diet plan,” he added.

Expert Takeaways

The study researchers have only produced an abstract and poster presentation, and many in the health industry await more details.

Ms. Routhenstein stated that the amount one eats within a time-restricted window matters regarding long-term health. “Time restricted eating within an 8-hour window may cause an increase in metabolic load, which is essentially eating too much at one time where the body struggles with digesting that meal, so free fatty acids flood the bloodstream leading to increases in triglycerides and insulin. This increase in triglycerides and insulin can negatively impact cardiometabolic health, which increases the risk of heart disease and its complications,” she wrote.

Dr. Bhojraj’s key takeaway message: “As a cardiologist who now focuses heavily on functional medicine, preventative cardiology, and longevity medicine, this ‘study’ will do absolutely nothing to change my practice patterns. If anything, I hope this study increases awareness of intermittent fasting/time-restricted eating and allows me to discuss the true benefits and risks with my patients.”

According to Mr. Zhong, the research clearly shows that a shorter eating duration was not associated with living longer. “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 said in the press release.

The AHA’s press release noted that all AHA press releases, meetings, and research abstracts are considered preliminary until published in a peer-reviewed journal. The editor’s note also cautioned, “As with any new science development, patients should always consult with their doctor prior to making changes to their health regimens.”

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