Intermittent Fasting Won’t Raise Your Risk Of A Heart Attack, Say Cardiologists
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For the past decade, intermittent fasting dominated diet trends. (ICYMI, intermittent fasting means that you don't eat for a set period of time each day or week.)
Recently, preliminary research presented at a recent American Heart Association (AHA)’s Epidemiology and Prevention, Lifestyle and Cardiometabolic Scientific Sessions suggests that people who ate all of their day's calories in an eight-hour window—a type of intermittent fasting—had a 91% higher risk of death from cardiovascular disease.
“We were surprised to find that people who followed an 8-hour, time-restricted eating schedule were more likely to die from cardiovascular disease," Victor Wenze Zhong, PhD, who led the study, said in a press release. Though Zhong noted that the diet has been popular due to short-term benefits like weight loss, lower insulin levels, and lower blood pressure, he said "our research clearly shows that... a shorter eating duration was not associated with living longer."
But don't throw out your fasting schedule out the window just yet, say experts.
"Unfortunately, this is the kind of research that gives nutrition science a dubious reputation," says Dr. Dariush Mozaffarian, PhD, a cardiologist and director of Tufts University's Food is Medicine Institute. "Right now, the evidence suggests that time-restricted eating—or intermittent fasting—is a reasonable approach for people if it works well for them."
Meet the experts: Dr. Dariush Mozaffarian, PhD, a cardiologist and director of Tufts University's Food is Medicine Institute. Dr. Ernst von Schwarz, MD, PhD, a cardiologist and the author of The Secrets of Immortality.
Here's everything we know about how intermittent fasting can affect and heart health.
What is intermittent fasting?
“Intermittent fasting is when you allow yourself to eat only during a specified window of time each day,” Alissa Rumsey, RD, a NYC-based dietitian and the owner of Alissa Rumsey Nutrition and Wellness, previously told WH.
The practice typically involves fasting for a certain number of hours spaced out during the week, says Sonya Angelone, RD, a San Francisco-based dietitian and a former chair of the AHA's nutrition committee, previously told WH. But she added that there's no "right" way to intermittent fast. One popular method of intermittent fasting is the 16:8 diet, in which you only eat for eight hours of the day.
What was the study testing?
The new study followed more than 20,000 American adults, half of whom were men and half of whom were women. The group had an average age of 49 years old.
The group completed two interviews about what time they ate during the previous day. Researchers then calculated their average eating windows and assumed their typical schedule for the rest of the study, which followed participants for an average of eight years.
The study aimed to look at intermittent fasting's effects on long-term health, since there had previously not been any studies that followed participants for more than a year. Researchers looked into the long-term health impacts of the group that only ate within eight hours of the day.
The findings presented on March 18 suggested that people who consumed all of their food across fewer than eight hours per day had a 91% higher risk of death due to cardiovascular disease. Researchers say time-restricted eating did not reduce the overall risk of death from any cause.
This contradicts prior research which followed participants for a shorter period of time—and found that intermittent fasting can result in improvements like lower insulin levels and blood pressure, which are hallmarks of heart health.
A 2018 study published in Cell Metabolism showed that some patients experienced weight loss and significantly lower blood pressure and insulin levels. High blood pressure increases the risk of heart failure, per Mayo Clinic, while high insulin levels can contribute to diabetes, obesity, and cardiovascular disease, according to the Cleveland Clinic.
"It’s crucial for patients, particularly those with existing heart conditions or cancer, to be aware of the association between an eight-hour eating window and increased risk of cardiovascular death," Zhong said in a press release.
However, the researchers did not find that intermittent fasting caused cardiovascular death. “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," Zhong added in the release.
What are the study's limitations?
Cardiologists quickly found limitations in the research. First, only an abstract was presented at the conference. That means that the full study has not been published or peer-reviewed, according to Mozaffarian. In an email to WH, Zhong noted that the study's results "may change" before publishing, "because reanalysis is common when addressing reviewers' comments."
Furthermore, only two interviews were used to determine a subject's eating pattern, Dr. Ernst von Schwarz, MD, PhD, a cardiologist and the author of The Secrets of Immortality, pointed out. Since the data was self-reported instead of administered in a controlled environment, Dr. von Schwarz says there's a "question" of reliability.
Plus, Mozaffarian notes the people studied were not intermittent fasting "in a conscious or even intentional way." Instead, they simply reported when they ate during the previous day. This means that they're likely missing meals for reasons other than health, he says. "To call that intermittent fasting is just wrong," he says.
Finally, the findings do not discuss what participants are eating. That, along with the total amount of food eaten, likely has a "larger impact" on heart health than the timing of meals, says Dr. von Schwarz. "At this point, we have no evidence that any intermittent fasting has negative effects for cardiovascular health," he says.
Mozaffarian says it's important that researchers dig further into this topic, in the hopes of one day providing more concrete eating guidelines.
"We should be shouting from the rooftops for more science to understand what we need to eat, how to eat, and when to eat," he says. "We can say with confidence what a healthy diet is, but I don't think we can say with any confidence if when we eat makes a difference in our health."
What does this mean for people who practice intermittent fasting?
Currently, people who have seen short-term health benefits from intermittent fasting shouldn't change their lifestyles, Dr. von Schwarz says.
At this time, there haven't been enough studies to determine the long-term health benefits of intermittent fasting, Mozaffarian notes. But, he pointed to short-term studies (lasting about a year or less) showing benefits for some individuals.
Currently, there isn't enough research to know if intermittent fasting affects women differently than men, adds Mozaffarian.
"This is one abstract—not even a published paper—and its methods are not addressing the question that was asked," he says. "Don't let one study completely change established science and throw you off track of what you know and what you practice."
Is intermittent fasting safe?
Yes, intermittent fasting is safe, as long as you are not experiencing a "severe endocrinologic disease" like uncontrolled diabetes, Dr. von Schwarz says.
The most important thing is the diet itself, not the timing, Mozaffarian adds.
"It depends on what you eat," he explains. "For some people, if intermittent fasting helps them avoid unhealthy foods and resets their metabolism and cravings, then that's great. As long as they're focused on eating healthy food. For other people, it may not work."
Intermittent fasting isn't a hard yes or no for everyone, so you should always chat with your doctor or a registered dietitian to make sure it's a good fit for you, he says.
"People have practiced intermittent fasting for other reasons—for religion, for spiritual reasons—for thousands of years," he says. "I think if it's done correctly—with intention and with care about what you're eating—I think it can help some people. For others, it won't work. Really, I think it adds some flexibility in ways to try to eat better and lose weight."
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