Intermittent Fasting Linked to Higher Risk of Death From Heart Disease, Preliminary Study Finds

The findings were recently presented at an American Heart Association (AHA) scientific conference.

Victor Wenze Zhong, a co-author of the research and epidemiologist at Shanghai Jiao Tong University, tells NBC News' Aria Bendix that it's too early to make recommendations about fasting based on the findings.

"There is nothing here that would suggest I make any clinical recommendations one way or the other," adds Sean P. Heffron, a cardiologist at NYU Langone Heart who did not contribute to the findings, to Today.com's Linda Carroll.

The research only identified a correlation between intermittent fasting and mortality—it did not show the eating pattern causes heart disease deaths—and other factors could be at play in this relationship. But Penny Kris-Etherton, a dietitian and member of the AHA nutrition committee, tells NBC News that people could "maybe consider a pause in intermittent fasting until we have more information or until the results of the study can be better explained."

Time-restricted eating, a type of intermittent fasting that involves only eating during certain time periods each day, has previously been linked to better blood pressure, blood sugar and cholesterol levels, according to a statement from the AHA. But some of the earliest studies were in mice, and most of the human trials that followed were small and only lasted one to three months, writes the Washington Post's Anahad O'Connor.

The new research involved participants who recalled what they ate for two 24-hour periods as part of the National Health and Nutrition Examination Survey between 2003 and 2018. The researchers used the times people recalled eating during these two days to determine whether they were intermittently fasting.

To gather information on participant death, the team used the National Death Index. All participants were at least 20 years old, around half were men, and 73 percent self-identified as non-Hispanic white adults. The researchers followed participants for around eight years on average. People who ate all their food in less than eight hours were 91 percent more likely to die from heart disease during the study period than people who ate throughout a 12- to 16-hour window.

The study did not make conclusions about why this trend appeared. But Zhong tells NBC News that people who ate only during eight-hour periods had lower levels of lean muscle mass, which has been associated with risk of cardiovascular death in a recent study.

Importantly, the findings come with several caveats. Reliance on self-reported eating habits, which both could be remembered incorrectly or may not be representative of participants' typical eating, is one limitation of the study, per the AHA's statement.

Dietary recall "is imperfect," Deepak Bhatt, a cardiologist at Mount Sinai Fuster Heart Hospital who did not contribute to the findings, tells Today.com. "People often don't recall what they had for breakfast. For this sort of research, you need detailed dietary information gathered in real time."

Additionally, the amount of data on each participant's eating habits is small. "It's a retrospective study looking at two days' worth of data, and drawing some very big conclusions from a very limited snapshot into a person's lifestyle habits," Pam Taub, a cardiologist at the University of California, San Diego, who was not involved in the research, tells NBC News.

Other researchers would like to see more information on what people were eating and what factors may have affected their eating habits. For instance, the participants did not record whether they were trying intermittent fasting as a choice. Some people could have had restricted eating windows because of health conditions or treatments that affected their appetites, Benjamin Horne, an epidemiologist at the Intermountain Heart Institute who was not involved in the research, tells New Scientist's Clarissa Brincat.

Christopher Gardner, who studies nutrition at Stanford University and did not contribute to the findings, tells the Washington Post that he would want to look at possible demographic differences between study participants.

"Did they all have the same level of disposable income and the same level of stress?" Gardner tells the publication. "Or is it that the people who ate less than eight hours a day worked three jobs, had very high stress and didn't have time to eat?"

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