Study details and key findings

During intermittent fasting, people only eat during a six-to-eight-hour time period each day before fasting for the remaining 16 to 18 hours. The diet has grown in popularity over the last decade, and some research suggests it can help with weight loss, reduce the risks of certain diseases, lower blood pressure, and more.

For the analysis, researchers from Shanghai Jiao Tong University School of Medicine in China examined information on dietary patterns taken from CDC's National Health and Nutrition Examination Surveys from 2003 and 2018. They also compared this data to people who had died in the United States between 2003 and December 2019. Mortality data was taken from CDC's National Death Index database.

Among the roughly 20,000 adults, the average age was 49 years, and the median length of follow-up was eight years. The longest follow-up period was 17 years.

Overall, the researchers found that people who typically ate all of their food across less than eight hours a day had a 91% higher risk of death from cardiovascular disease. This increased risk was also seen in those living with heart disease or cancer.

Among individuals with existing cardiovascular disease, an eating duration between eight and 10 hours a day was linked to a 66% increased risk of death from stroke or heart disease.

In general, time-restricted eating did not decrease the overall risk of death from any cause among the participants. However, an eating duration of longer than 16 hours a day was associated with a reduced risk of cancer mortality among people with cancer.

"We were surprised to find that people who followed an 8-hour, time-restricted eating schedule were more likely to die from cardiovascular disease," said Victor Wenze Zhong, a professor and chair of the department of epidemiology and biostatistics at the Shanghai Jiao Tong University School of Medicine and the study's senior author. "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."

So far, the analysis has not been peer-reviewed or published in an academic journal. The researchers also acknowledged several limitations to the study, including its use of self-reported dietary information and the fact that the nutritional quality of the foods eaten was not considered.

Commentary

According to experts, it's too early to make any specific recommendations about intermittent fasting based on the analysis alone.

"While informative, this study should be considered exploratory," said Harlan Krumholz, a leading expert in the science of improving health policy at Yale University. "We are still learning about how people can optimize their diets, and this study is more of a call for more research than something that should frighten people who find restricted eating a useful strategy."

According to Zhong, "practicing intermittent fasting for a short period such as 3 months may likely lead to benefits on reducing weight and improving cardiometabolic health." However, he added that people "should be extremely cautious" about intermittent fasting for longer periods of time, such as years.

Similarly, Benjamin Horne, a research professor at Intermountain Health, said the analysis "doesn't change my perspective that there are definite benefits from fasting, but it's a cautionary tale that we need to be aware that there are definite, potentially major, adverse effects."

Although intermittent fasting might have long-term benefits, the added stress from fasting may lead to short-term risks of heart problems, especially among more vulnerable groups. "In the long term, what it does is reduces those risk factors for heart disease and reduces the risk factors for diabetes and so forth — but in the short term, while you're actually doing it, your body is in a state where it's at a higher risk of having problems," Horne said.

Penny Kris-Etherton, emeritus professor of nutritional sciences at Penn State University and a member of the American Heart Association's nutrition committee, also urged people to be cautious with intermittent fasting until more is known about its health impacts.

"Maybe consider a pause in intermittent fasting until we have more information or until the results of the study can be better explained," she said. (Bendix, NBC News, 3/18; Nazzaro, The Hill, 3/18; American Heart Association press release, 3/18; Herper, STAT, 3/19)

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