Intermittent fasting each day boosts risk of cardiovascular death, analysis reveals

NEW YORK, March 18 (UPI) -- People who restricted their eating across fewer than eight hours per day had a 91% higher risk of cardiovascular death than those who ate across 12 to 16 hours per day, an analysis of more than 20,000 U.S. adults reveals.

The preliminary research was presented Monday at the American Heart Association's Epidemiology and Prevention│Lifestyle and Cardiometabolic Scientific Sessions 2024 in Chicago. The meeting is intended to offer the latest science on population-based health and wellness and lifestyle implications.

"Our study is the first investigation to examine the association between eight-hour, time-restricted eating and mortality," senior author Victor Wenze Zhong, a professor and department chair of epidemiology and biostatistics at Shanghai Jiao Tong University School of Medicine in China, told UPI via email.

However, the findings still need replication and can't prove that eight-hour, time-restricted eating causes cardiovascular death. They also don't support long-term use of this approach for preventing cardiovascular death and for improving longevity, he said.

Meanwhile, Zhong noted that "time-restricted eating has gained popularity as a dietary intervention that limits food consumption to a four-to-12-hour window each day."

Previous research has found that time-restricted eating -- a type of meal timing that falls under intermittent fasting -- improves several cardiometabolic health measures such as blood pressure, blood glucose and cholesterol levels.

However, Zhong said, those findings were based on short-term, randomized, controlled trials, generally conducted within a one-month-to-one-year period, not long-term studies.

"We had expected that long-term adoption of eight-hour, time-restricted eating would be associated with lower risk of cardiovascular death and even all-cause death," said Zhong, who has a doctorate in nutritional epidemiology from the University of North Carolina-Chapel Hill.

The researchers also found an increased risk of cardiovascular death in people living with heart disease or cancer. Among those with existing cardiovascular disease, an eating duration of no fewer than eight but fewer than 10 hours per day also was associated with a 66% higher risk of death from heart disease or stroke.

The study was unable to explain the underlying mechanisms driving the observed association between eight-hour restricted eating and cardiovascular death, Zhong said.

But the researchers observed that people who restricted eating to a period fewer than eight hours per day had less lean muscle mass compared with those with a typical eating duration of 12 to 16 hours, he said. Loss of lean body mass has been associated with a higher risk of cardiovascular mortality.

Time-restricted eating did not decrease the overall risk of death from any cause. Meanwhile, an eating duration of more than 16 hours per day was linked to a lower risk of cancer mortality among people with cancer.

"All the evidence that we have from short-term clinical studies basically shows many cardiovascular benefits of time-restricted eating," Penny Kris-Etherton, a registered dietitian and member of the American Heart Association's nutrition committee, told UPI in a telephone interview. She was not involved in the new research.

That's why "a 91% higher risk of cardiovascular death in people who participate in an eight-hour time restricted eating program is really, really surprising," said Kris-Etherton, who also is a professor emeritus of nutritional sciences at Penn State University in University Park, Pa.

Various factors may account for the association between an eight-hour eating window and increased mortality, Dr. Karen Aspry, chair of the nutrition workgroup at the American College of Cardiology, a medical society, told UPI via email.

This includes depleted electrolytes (low potassium magnesium or both), increased adrenaline levels and reduced protein synthesis due to inadequate intake throughout the day, Aspry said

Time-restricted eating also does not require intake of high-quality foods. As a result, "any mortality associations could be due to consumption of nutrient-poor foods, or even fast or ultra-processed foods," said Aspry, who is director of Lifespan Cardiovascular Institute's lipid and prevention program and an associate professor of medicine at the Warren Alpert Medical School of Brown University in Providence, R.I.

"This is a significant study that should give pause to individuals who promote or follow short-window time-restricted eating," she said. "It drives home an important point: Weight loss from dieting does not automatically equate to health even if it lowers blood pressure, cholesterol, glucose or inflammatory markers."

Concerns still linger about the risks of time-restricted eating that the study did not address, Dr. Joseph Rogers, a cardiologist and president and chief executive officer of the Texas Heart Institute in Houston, told UPI via email.

The analysis "highlights a concerning signal regarding the risks of time-restricted eating," Rogers said.

"There are many remaining questions regarding the analysis, including how accurately the study participants recalled their diet, the quality and content of the food they consumed, and a lack of detail regarding the cause of increased deaths in the study group. It is also critical for future research to define the biological basis underlying this observation," he said.

Interpreting the findings appropriately will require knowing more about any other potential differences between the people who restricted their eating across fewer than eight hours and those who ate across 12 to 16 hours per day, Christopher Gardner, director of nutrition studies at the Stanford Prevention Research Center in Palo Alto, Calif., told UPI via email.

"For example, what if those eating in a shorter time period had less access to food, worked more work shifts and experienced more life stress compared to those in the 12- to 16-hour category?" asked Gardner, who also is a professor of medicine at Stanford University.

In addition, "the way the study participants were determined to be 'intermittent fasters' involves some important limitations," he said. "That characterization is based on two days of diet data."

Until more details are known, he said, "a good dose of healthy skepticism is likely the most important way to approach these new and interesting findings."