Intermittent fasting and heart disease: the 91% study, explained

In March 2024, a study presented at an American Heart Association meeting made headlines. It linked eating within less than eight hours a day to a 91% higher risk of dying from cardiovascular disease. The researchers, led by epidemiologist Victor Wenze Zhong, used US national survey data from 2003 to 2018 covering more than 20,000 adults. They compared people with a short eating window to people who ate across 12 to 16 hours a day, and checked the results against death records up to 2019. They also found that time-restricted eating didn't lower the overall risk of death.

Experts were quick to question the findings. The study hadn't been published in a peer-reviewed journal. Each person's eating window came from two questionnaires, filled in less than two weeks apart, asking what time they had eaten the day before. That average was then treated as their usual habit for years. Only 414 people were in the eight-hour group, and they differed from the others in other ways, for example they were more likely to smoke. Most importantly, the study showed a link, not a cause: it didn't show that eating this way leads to heart disease.

The longest intermittent fasting trials so far have lasted about a year. Earlier research found that intermittent fasting improves blood pressure, blood sugar and cholesterol. One headline isn't the full picture.

General information, not medical advice. Don’t fast without talking to a doctor if you’re pregnant or breastfeeding, under 18, have had an eating disorder, have diabetes, or take insulin or other medicine that lowers blood sugar.