8-hour intermittent fasting tied to 90% higher risk of cardiovascular death, early data hint

Intermittent fasting — a dieting strategy that limits when someone can eat each day — has been linked to a 91% higher risk of heart-related death in a large study. This risk was tied to eating in an eight-hour or shorter window in the 24-hour day, compared with a more typical 12- to 16-hour window.

The new, preliminary research was presented March 18 at the American Heart Association (AHA) EPI Lifestyle Scientific Sessions 2024. It looked at deaths from cardiovascular diseases in more than 20,000 U.S. adults, who were followed for an average of eight years.

Experts told Live Science that the study highlights a need to exercise caution around the use of intermittent fasting. However, one noted that, until all the data from the study is published, it's difficult to say whether the time window or types of food consumed are more relevant to a person's risk of death.

"It's quite possible to eat a really low-quality diet while time-restricted eating," Christopher Gardner, professor of medicine at Stanford University, told Live Science. It may also be that some participants with restricted eating windows were facing food insecurity and not eating well or enough, he added. "We don't know everything yet. I'll wait for more," he said of the new research.

Related: 9 heart disease risk factors, according to experts

'There is so much that isn't known'

Intermittent fasting involves eating only during a specific window of time each day, often between four and 12 hours out of 24. Previous research suggests that intermittent fasting improves metrics tied to cardiovascular health in the short term, over a few months, including measures of insulin resistance.

Of the 20,000 people in the new study, 414 reported eating in time windows of eight hours or less each day. Participants were not assigned diets to follow, but rather, their typical diets were assessed through two surveys, in which participants recalled everything they'd eaten in two 24-hour time frames.