A study of more than 20,000 adults in the US found that those who followed a type of intermittent fasting, where they ate eight hours a day, had a 91% higher risk of dying from cardiovascular disease compared to those who ate 12-16 hours a day.

In the preliminary study, researchers reviewed information on dietary patterns for participants in the annual US National Health and Nutrition Examination Surveys from 2003 to 2018 and compared it with data on people who died in the US from 2003 to in 2019, from the Centers for Disease Control and Prevention’s National Death Index database.

They found that time-restricted eating did not reduce the overall risk of death from any cause. In contrast, those who followed intermittent fasting by eating for eight hours a day had a 91% increased risk of dying from cardiovascular disease.

They found that the increased risk of cardiovascular death was also seen in people living with heart disease or cancer. Also, among people with existing cardiovascular disease, eating less than ten hours a day was associated with a 66% higher risk of dying from heart disease or stroke.

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

“Restricting daily eating time to a short period of time, such as eight hours a day, has gained popularity in recent years as a way to lose weight and improve heart health,” says lead study author Victor Wenze Zhong, professor and chairman of the Department of Epidemiology and Biostatistics at Shanghai Jiao Tong University School of Medicine in Shanghai, China.

“Although this type of diet has been popular because of its potential short-term benefits, our research clearly shows that, compared to a typical feeding time range of 12-16 hours per day, shorter feeding time was not associated with longer lifespan,” he adds.

Limitations of the study included its reliance on self-reported dietary information, which may be affected by participants’ memory and may not accurately assess typical dietary habits. Factors that may also play a role in health, other than daily duration of food consumption and cause of death, were not included in the analysis.

“Overall this study suggests that time-restricted food consumption may have short-term benefits, but long-term adverse effects. When the study is presented in its entirety, it will be interesting and useful to learn more details of the analysis, such as the nutrient quality of the diets of various subgroups of participants,” says Christopher Gardner, professor of medicine at Stanford University in California and chair of the editorial board of the American Heart Association’s 2023 dietary guidelines scientific statement.

He notes that it will also be critical to see whether a comparison of demographic and other participant characteristics and traditional cardiometabolic risk factors, such as weight and stress, has been included.

Preliminary research results were presented at an American Heart Association conference in Chicago.