Health

New intermittent fasting study had 'surprisingly' negative results

While recent studies suggest time-restricted eating can help people lose weight, new research raises significant questions about risks of the method.

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Intermittent fasting has long been a popular way for people to lose weight and trim body fat, but new research had "surprising" results that prompted concern from researchers. 

Research presented Monday indicated that those who only ate for eight-hour windows every day had a 91% higher risk of cardiovascular death compared to those who ate meals throughout the day (12-16 hours). The research was presented at the American Heart Association’s Epidemiology and Prevention│Lifestyle and Cardiometabolic Scientific Sessions 2024

Given that increased body fat has been linked to a higher risk of cardiovascular deaths, the study's lead author noted his shock by the results. 

“We were surprised to find that people who followed an eight-hour, time-restricted eating schedule were more likely to die from cardiovascular disease. 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,”  said senior study author Victor Wenze Zhong.                                                                                   

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The study included 20,000 adults in the U.S. with an average age of 49 years. It followed them for a median length of eight years. 

Previous research has suggested that time-restricted eating can help lead to weight loss. According to an analysis from researchers at the University of Chicago, intermittent fasting was just as effective as calorie counting for weight loss. 

The average person who ate meals between noon and 8 p.m. lost 10.6 pounds.

“Restricting daily eating time to a short period, such as 8 hours per day, has gained popularity in recent years as a way to lose weight and improve heart health,” said Zhong. “However, the long-term health effects of time-restricted eating, including risk of death from any cause or cardiovascular disease, are unknown.”

The authors noted that there were several limitations to the new study. For instance, researchers have not been able to examine if intermittent fasters eat the same nutrients as those who eat throughout the day. Researchers also noted that intermittent fasters may face stress and other factors that would cause an increased risk for cardiovascular death. 

“Overall, this study suggests that time-restricted eating may have short-term benefits but long-term adverse effects. When the study is presented in its entirety, it will be interesting and helpful to learn more of the details of the analysis,” said Christopher D. Gardner, professor of medicine at Stanford University.

The University of Chicago says the following groups should not consider intermittent fasting: 

- Those who are pregnant or lactating. 

- Children under 12. 

- Those with a history of disordered eating. 

- Those with a body mass index, or BMI, less than 18.5.

- Shift workers; studies have shown they may struggle with fasting regimens because of shifting work schedules. 

- Those who need to take medication with food at regimented times.