Intermittent fasting diets – which restrict eating to certain parts of the day and have been touted by Jennifer Anniston, Kourtney Kardashian and other celebrities – have become a popular way to lose weight in recent years. 

Some people follow the 5:2 diet, which calls for normal eating five days a week and restricting calories to 500-600 per day the other two. For the 8:16 diet, people restrict their eating to eight hours of the day and fast the remaining 16. One study even showed that intermittent fasting may be associated with longevity, acuity and leanness.

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But new research indicates that the 8:16 diet is actually detrimental to health, linking the eight-hour restricted eating time to higher risks of cardiovascular deaths.

The results from an analysis of more than 20,000 adults, presented at the American Heart Association’s scientific session in Chicago, revealed that those who restricted their eating to eight hours a day had a 91% higher risk of death from cardiovascular disease compared to those who ate across 12-16 hours per day.

The preliminary research, which has not yet been peer-reviewed or published in an academic journal, also showed that people with heart disease or cancer who followed 8:16 intermittent fasting had an increased risk of cardiovascular death and that limiting eating to less than eight hours a day did not lead to a longer life.

“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 senior study author Victor Wenze Zhong, a professor of epidemiology and biostatistics at Shanghai Jiao Tong University in China. “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.”

Further findings indicated that:

• Among people with existing cardiovascular disease, an eating duration of no less than 8 hours per day – but less than 10 – also was associated with a 66% higher risk of death from heart disease or stroke.

• Time-restricted eating did not reduce the overall risk of death from any cause.

• An eating duration of more than 16 hours per day was associated with a lower risk of cancer mortality among people with cancer.

For the study, researchers reviewed information about the dietary patterns of participants in annual National Health and Nutrition Examination Surveys between from 2003 to 2018.

Researchers compared data from the surveys to information from the U.S. Centers for Disease Control and Prevention’s National Death Index database about people who died in the United States from 2003 through 2019.