Intermittent Fasting Linked to 91% Higher Risk of Heart Disease, According to New Study

Learn what may be the culprit for this potential connection.

Reviewed by Dietitian Annie Nguyen, M.A., RD

Intermittent fasting—also known as time-restricted eating—has been “on-trend” for a while now. If you’re unfamiliar with it, essentially it's eating all of your meals during a set window of time. And there are different ways to do it.

For example, some forms of intermittent fasting allow for 8 or 5 hours to eat whatever you’re going to eat for the day—and then you fast the other 16 to 19 hours. Other intermittent fasting models alternate days of eating with days of fasting.

Proponents of intermittent fasting boast that it has many benefits, including weight loss and a reduction in insulin levels. When insulin levels are too high for too long, it increases the risk of obesity, type 2 diabetes and heart disease.

But while intermittent fasting seems to have short-term benefits, is it healthy and effective long-term? A new study that was presented on March 18, 2024, at the American Heart Association’s Epidemiology and Prevention—Lifestyle and Cardiometabolic Scientific Sessions 2024 suggests it might not be.

Before we share details about the study, a quick caveat: These findings were presented as an abstract, and are not yet published in a peer-reviewed scientific journal. The AHA notes, “Abstracts presented at the Association’s scientific meetings are not peer-reviewed, rather, they are curated by independent review panels and are considered based on the potential to add to the diversity of scientific issues and views discussed at the meeting. The findings are considered preliminary until published as a full manuscript in a peer-reviewed scientific journal.”

What Did This Study Find?

Researchers examined the data of 20,000 U.S. adults from the 2003 to 2018 National Health and Nutrition Examination Surveys (NHANES) and compared them to data of people who died from 2003 to December 2019 from the Centers for Disease Control and Prevention’s (CDC) National Death Index database.

The average age of the participants was 49—about half of them were women and there was a mix of races and ethnicities. They were followed for an average of eight years up to as long as 17 years. Participants were at least 20 years old and had filled out at least two 24-hour dietary recall questionnaires within the first year of enrollment.

The analysis found that people who followed a pattern of eating all of their food during a window of time that was less than 8 hours per day had a 91% higher risk of death due to cardiovascular disease.

Among people with existing cardiovascular disease, an eating window of 8 to 10 hours per day was associated with a 66% higher risk of death from heart disease or stroke.

“We were surprised to find that people who followed an 8-hour, time-restricted eating schedule were more likely to die from cardiovascular disease,” says senior study author Victor Wenze Zhong, Ph.D., a professor and chair of the Department of Epidemiology and Biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China, in the press release regarding the study. “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 to 16 hours per day, a shorter eating duration was not associated with living longer.”

How Does This Apply to Real Life?

Zhong emphasizes a more personalized approach to eating that is also based on current recommendations, like the 2020-2025 Dietary Guidelines for Americans.

“It’s crucial for patients, particularly those with existing heart conditions or cancer, to be aware of the association between an 8-hour eating window and increased risk of cardiovascular death,” urges Zhong. “Our study’s findings encourage a more cautious, personalized approach to dietary recommendations, ensuring that they are aligned with an individual’s health status and the latest scientific evidence.”

Zhong also offers a word of caution regarding the results. “Although the study identified an association between an 8-hour eating window and cardiovascular death, this does not mean that time-restricted eating caused cardiovascular death.”

In other words, the researchers could not prove that intermittent fasting caused death from heart disease. With that said, there may be an explanation for the intermittent fasting-heart disease link.

"Intermittent fasting itself is a stressor on the body, and in the context of our modern-day life that's already filled with chronic emotional, physiological and environmental stressors, intermittent fasting might do more harm than good,” Jillian Greaves M.P.H., RD, LDN told EatingWell in a previous article. “Fasting increases cortisol which can lead to blood sugar dysregulation, increased insulin resistance, lean muscle loss, fatigue and disruptions to thyroid function over time. In the short-term, fasting may lower thyroid stimulating hormone, but elevated cortisol on a persistent basis can reduce the conversion of thyroid hormone."

And, according to the CDC, chronic stress is a risk factor for heart disease. Cortisol increases blood pressure, and high blood pressure is a direct risk factor for heart disease. People who are chronically stressed out also tend to engage in habits that may harm their health—like stress eating and excessive alcohol intake. When we’re stressed, we also tend to not get enough quality sleep—which just exacerbates the stress cycle.

The Bottom Line

Researchers conducted this preliminary study because, while there is evidence that intermittent fasting may have some short-term benefits, there is very little data on its long-term efficacy and safety. And while this review suggests there may a link between time-restricted eating and dying from heart disease—whether you currently have heart disease or not—more research needs to be done to flesh out other possible connections and details.

If you engage in intermittent fasting, it’s important to be aware of the potential long-term risks of it. And if you’re going to do it, learn how to do it properly, as many people “wing it” and this can knock your circadian rhythms out of whack—which has also been associated with an increase in heart disease risk. Your best bet is to consult with your doctor before making any changes to your current eating regimen.

Read the original article on Eating Well.