Intermittent Fasting Probably Won’t Harm Your Heart If You Do It Right

Intermittent fasting has been under scrutiny since the American Heart Association (AHA) released information earlier this week from a study linking this eating pattern to a higher risk of death from heart disease. The findings, which have not been peer-reviewed or published, are stirring controversy.

According to the AHA press release, the study collected data from over 20,000 adults based on two days of eating, as part of a national survey conducted from 2003 to 2018. The researchers compared this information to data collected from people who died in the U.S. from 2003 through December 2019.

The researchers concluded that people who had an eating window of eight hours a day—which mimics the popular 16:8 intermittent fasting diet pattern—were 91% more likely to die of heart disease compared to those who ate over 12 to 16 hours a day, which is a more typical eating pattern.

The study also found that people who already had cardiovascular disease and ate over a period of fewer than 10 hours a day had a 66% higher risk of death from heart disease or stroke. Overall, following any form of time-restricted eating pattern did not lower the risk of dying from any cause, according to the findings.

Joseph Daibes, DO, an interventional cardiologist with Northwell Health, urges people to look into the details of studies before drawing major conclusions.

“I do not think the American Heart Association did any justice by putting out this abstract that was not fully complete and poorly designed, knowing that it would create a stir,” Daibes told Verywell. “I’m receiving phone calls asking if patients should stop their diet and change their lifestyle. There is no reason to do that based on these findings.”

There Are Red Flags to Address

The study has not yet been published—the AHA simply shared a press release about it—and it also hasn’t been peer-reviewed.

“Peer review is an important part of the medical publishing process to ensure accurate scientific inquiry and dissemination of research findings in a methodologically sound manner,” Megan Kamath, MD, a cardiologist at UCLA Health, told Verywell.

The data is also based on only two days of dietary intake.

“Two days of eating data is a limited amount of time when looking at outcomes such as cardiovascular and all-cause mortality,” Kamath said. She also noted that there is “limited information” about what people ate during their eating windows. “That would be helpful in analyzing this type of a study, as would other comorbidities that these patients have,” she said.

The study relied on survey data, meaning people filled out information about their eating habits. This can be tricky in science because people are not always entirely honest about what they ate and may also not fully remember what they had to eat or how much, Daibes said.

The study lacks information about other lifestyle risk factors for cardiovascular disease, like physical activity levels and tobacco and alcohol use.

Daibes suggested looking at these findings as “preliminary data for a study that might one day become larger.”

There Is Data to Support Intermittent Fasting for Health

One of the study’s researchers said in the AHA statement that he was “surprised” by the findings, given that most data has supported the use of intermittent fasting for heart health.

“We have data that show that intermittent fasting and time-restricted eating is beneficial for your health for many reasons,” Daibe said.

A meta-analysis of human and animal studies published in 2019 found that restricting eating windows was linked to a series of benefits, including a reduction in blood pressure, weight loss, and improved longevity.

Data has also shown that, while intermittent fasting can help a person lose weight, it’s no more effective than traditional calorie restriction. One study of 139 adults in China who had obesity found that those who followed an intermittent fasting diet lost about the same amount of weight and had similar cardiovascular health after a year as people who counted calories.

A randomized controlled trial of 116 people published in 2020 also found no significant differences in weight loss between people who didn’t eat from 8 p.m. until noon the next day (a 16:8 diet) and those who didn’t follow an intermittent fasting diet.

Daibes said intermittent fasting may help heart health indirectly by limiting the amount of insulin spikes you have a day.

“That is very helpful for your metabolism. Your baseline glucose will stay more stable during the day,” he said.

Intermittent fasting can also be a helpful tool for weight management in some people simply because maintaining a healthy weight is linked to good cardiovascular health, Daibes added.

Does Breakfast Make a Difference?

If you follow an intermittent fasting diet, some schools of thought say it’s best for your heart health not to skip breakfast, but Kamath said that’s still being explored.

“This is an area that has also been debated in the medical field,” she said. “Most of the thought behind not skipping breakfast surrounds the theory that breakfast jumpstarts your metabolism and breakfast eaters have healthier eating habits, but these have not been proven in large scale studies.”

Daibes agreed that the data isn’t conclusive on whether it’s bad to skip breakfast. But “breakfast should be your most calorie-dense meal, and the meals that follow should have less calories and be less heavy,” he said.

Ultimately, doctors said more robust research needs to be done to explore the potential benefits and drawbacks of following an intermittent fasting diet for cardiovascular health.

“We have seen previous studies show potential benefit [of intermittent fasting] with respect to obesity, blood pressure, and diabetes management, but further work needs to be done to understand this better,” Kamath said. “This is an area of medicine where we are still trying to understand what is best and more research needs to be done to make a formal recommendation in this space.”

How to Practice Intermittent Fasting in Healthy Way

Following a healthy diet during eating windows is crucial, Daibes said.

“You need to do time-restricted eating the right way,” he said. “You can’t say, ‘During those eight hours, I can eat whatever I want.’”

He recommends following a balanced, mostly plant-based diet that includes plenty of greens, with some white meats and fish.

“It’s been proven time and again that the Mediterranean diet is best for cardiovascular outcomes,” he said.

If you plan to follow an intermittent fasting diet, Kamath recommends checking in with your doctor first to “take into consideration individual medical conditions and long-term goals for health.”

If your budget allows, it may be helpful to consult with a registered dietitian as well to make sure you’re eating well during eating windows, Daibes said.

“I send a good amount of patients to nutritionists to have a discussion about what the food intake should be,” he said.