Could intermittent fasting lead to a higher risk of cardiovascular death? Recent research suggests so, while some experts are wary of the findings

By Lisa Marie Basile | Fact-checked by Davi Sherman
Published March 26, 2024

Key Takeaways

  • Recent findings from the American Heart Association’s Epidemiology and Prevention Lifestyle and Cardiometabolic Scientific Sessions suggest a concerning 91% increased risk of cardiovascular death for individuals with eating windows shorter than eight hours.

  • Experts highlight limitations in the research, such as its reliance on self-reported data, lack of diversity in participants, and utilization of only two questionnaires, cautioning against drawing definitive conclusions.

According to research presented at the American Heart Association’s (AHA) Epidemiology and Prevention Lifestyle and Cardiometabolic Scientific Sessions recently, an eating window of less than eight hours per day—known as time-restricted eating (TRE) or intermittent fasting (IF)—was associated with 91% higher risk of death due to cardiovascular disease.[] 

The researchers also found that TRE did not reduce the overall risk of death from any cause. An abstract—which has not been peer-reviewed—is currently available.[] []

The researchers compared data on participants' dietary patterns in the 2003–2018 National Health and Nutrition Examination Survey (NHANES) to data on people who died in the U.S. from 2003–2019 from the Centers for Disease Control and Prevention’s (CDC) National Death Index database. The team looked at over 20,078 participants, half of whom self-identified as men and 73.3% of whom self-identified as non-Hispanic white adults. All study participants were followed for over eight years.[] 

Of the 20,078 participants, 414 were in the eating group that ate during an <8-hour window. The researchers utilized two 24-hour self-reported dietary recall questionnaires taken less than two weeks apart from this group. The two questionnaire responses were intended to represent a glimpse into those participants’ average eating windows.[] 

Senior study author Victor Wenze Zhong, PhD, a professor and chair of the Department of Epidemiology and Biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China, tells MDLinx, “We controlled for age, sex, race/ethnicity, education, income, food insecurity, smoking, drinking, physical activity, total energy intake, BMI, and self-reported diabetes, hypertension, dyslipidemia, cardiovascular disease, and cancer.” 

The study found that a less than eight-hour eating window (versus a 12- 16-hour eating window) was associated with a significantly higher risk of cardiovascular mortality in the general population as well as in adults with cardiovascular disease or cancer.[] 

The 414 people in the less than eight-hour eating group tended to be younger and less educated, have lower income and less access to food, and be more likely to smoke. The mean BMI of this group—29.9—was also higher than that of the others.[][]

A closer look at intermittent fasting TRE or IF involves intentionally limiting caloric intake to a specific window—and it’s become increasingly popular in the health and wellness space over the last few years. Many IF enthusiasts eat between 12 p.m. and 8 p.m., for example.[][]

As the AHA stated in its news release, “Previous research has found that time-restricted eating improves several cardiometabolic health measures, such as blood pressure, blood glucose and cholesterol levels.” More so, IF has been shown to improve specific diseases, like rheumatoid arthritis and other inflammatory arthritic conditions, and prevent age-related memory loss and issues related to menopause.[][][][] 

Given that prior research indicates IF’s positive impact, the team’s research has caused a stir, especially among patients wondering whether IF will lead to cardiovascular mortality. 

“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,” Dr. Zhong told the AHA. “Although the study identified an association between an eight-hour eating window and cardiovascular death, this does not mean that time-restricted eating caused cardiovascular death.”[]

The New York Times reported that Dr. Zhong said his study was not designed to answer whether IF is really harmful.[]

The AHA also notes, “Statements and conclusions of studies that are presented at the American Heart Association’s scientific meetings are solely those of the study authors and do not necessarily reflect the Association’s policy or position.”

What do the experts make of the research?

“There are so many limitations with this study,” says Yu-Ming Ni, MD, board-certified cardiologist and lipidologist at MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, CA. 

First, he says, the self-reported questionnaire—of which there were only two—is a notable limitation. “There wasn’t anyone checking if they ate within that window or why they’re only eating 8 hours per day.” He also notes that IF was a lot less popular between 2008 and 2013, so the participants were likely not utilizing IF for weight loss or health purposes.

“I suspect that many patients in this study who were eating [for fewer] than 8 hours per day were doing so not because they were trying to lose weight. I suspect that they had a problem of some kind that they only ate for that long,” Dr. Ni says. 

Cheng-Han Chen, MD, a board-certified interventional cardiologist and Medical Director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA, agrees, noting that without complete study data being published, and without the baseline demographics and comorbidities of each TRE group (in addition to any participant biases), it’s hard to settle on the conclusion that IF is associated with higher risk of cardiovascular mortality. 

Dr. Chen says he would still recommend IF to his patients for improvements in weight, blood sugar control, cholesterol levels, and general cardiovascular health.

Dr. Ni says that findings like these “light up the news” because they sound fascinating, but he is unhappy about the research team’s very decisive conclusion. Additionally, he says that he suspects the abstract would have been “ripped apart” in a peer review. 

He recommends that patients read these findings with caution, as there are many flaws in the study. “Any association study that looks at lifestyle should know that our decisions in life are not made in a vacuum.”

“Maybe they [did the research] for a good purpose, but what happens is if you jump to conclusions that are too overreaching for what your study has actually done, you start to lose track of the real story behind the finding,” Dr. Ni stresses. “That is the dangerous part about this.” 

Like Dr. Chen, Dr. Ni also says that he sees IF as a reasonable dietary pattern, especially for patients who want to curtail late-night snacking, which can result in harmful health conditions. “I’m not discouraged based on these findings,” he says. 

Another key issue? The study’s overwhelmingly white participant population, says Nieca Goldberg, MD, Medical Director at Atria NY and Clinical Associate Professor of Medicine at NYU Grossman School of Medicine. “It is clear that more research has to be done in a more diverse population. We need a better understanding of the science leading to increased cardiovascular death.”

Dr. Goldberg also notes that for patients wanting to lose weight, it could be possible that “short-term, intermittent fasting under a provider’s supervision can jump-start a patient’s weight loss program, but that it may not be for long-term prescription.”

Matthew Landry, PhD, RDN, Assistant Professor of Population Health & Disease Prevention at UCI Public Health, says he wouldn’t recommend that patients change their use of IF based on this study alone and that he would remind patients that it’s “probably still more important to focus on what you’re eating rather than when.” Landry says that it’s also possible that some of the benefits observed with IF may result from being more intentional and mindful about food. 

“Until we better understand the biological mechanism that may link IF and adverse cardiovascular outcomes, I wouldn’t put much weight on these findings,” he says. 

Dr. Zhong tells MDLinx that he doesn’t know when the full study will be available.

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