'We were surprised': Intermittent fasting flagged as serious health risk

Intermittent fasting, a trendy method for weight-loss and targeting inflammation, has been flagged as a serious health risk, the American Heart Association announced Monday.

Results of a study presented at the association's conference in Chicago this week revealed that adults following an eight-hour time-restricted eating schedule have a 91% higher chance of death by cardiovascular disease than those eating within the usual timeframe of 12-16 hours per day.

Though it is important to note that these are preliminary findings, said senior study author Victor Wenze Zhong, chair of the Department of Epidemiology and Biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China.

"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," Zhong said at the event.

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How the study was conducted, what else it showed

The American Heart Association studied approximately 20,000 adults in the U.S. from 2003 to 2018 using data collected by the Centers for Disease Control and Prevention (CDC) for its National Health and Nutrition Examination Survey. The association tracked dietary patterns in people with an average age of 49 who documented their food intake for at least two days within one year, the organization reported.

That data was then compared to CDC mortality data from the same time period.

About half of the participants self-identified as women. Over 73% of the participants self-identified as non-Hispanic white adults, 11% self-identified as Hispanic and 8% self-identified as non-Hispanic Black adults. Data was collected on an additional 6.9% that self-identified as another racial category.

Details of the findings, published by the American Heart Association, include the following:

• People with a pattern of eating less than eight hours per day had a 91% higher risk of death by cardiovascular disease.
• Increased risk of cardiovascular death was also seen in people living with heart disease or cancer.
• Eating between eight and 10 hours per day was associated with a 66% higher risk of death from heart disease or stroke for those with existing cardiovascular diseases.
• Intermittent fasting did not decrease the overall risk of death from any cause.
• For those living with cancer, an eating duration of 16 hours per day or more lowered the risk of cancer mortality.

Further study is needed, experts say

Not all factors that play a role in overall health were considered in this study. Future research seeks to "examine the biological mechanisms that underly the associations between a time-restricted eating schedule and adverse cardiovascular outcomes," the American Heart Association reported. Also needed is insight on whether or not the findings will be similar depending on where participants live in the world.

There is research showing that intermittent fasting could improve "cardiometabolic health measures such as blood pressure, blood glucose and cholesterol levels," according to the American Heart Association.

“We were surprised," Zhong said. "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."

The most critical piece to this discovery, though, is the increased risk for those already living with heart conditions or cancer.

"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,” said Christopher Gardner, director of nutrition studies at Stanford University.

Gardner noted that the "nutrient quality of the diets" needs to be examined. "Without this information, it cannot be determined if nutrient density might be an alternate explanation to the findings that currently focus on the window of time for eating."