Intermittent Fasting and Heart Health

Experts say losing weight is beneficial for heart health, but there is little research on the long-term impact of intermittent fasting.

Intermittent fasting has grown in popularity as a weight loss solution. When asked whether they had followed a specific diet in the past year, 13% of American adults said they had tried intermittent fasting, according to a 2024 online survey from the International Food Information Council.

However, there is ongoing debate about intermittent fasting’s health benefits. While it has been shown to help people lose excess pounds, intermittent fasting is often labeled as a fad diet. In addition, a retrospective study presented at an American Heart Association conference in March 2024 claimed intermittent fasting was linked to a higher risk of death from heart disease.

What is the truth? Parveen Garg, MD, a cardiovascular disease specialist with the USC Cardiac and Vascular Institute, part of Keck Medicine of USC, says being overweight or obese is the greater health threat. “We know that weight loss reduces your overall risk for heart disease in the long term,” Dr. Garg says. “If intermittent fasting helps with weight loss, that’s great.”

At the same time, he emphasizes that more robust research is needed to verify the safety and usefulness of intermittent fasting when followed for extended periods.

What is intermittent fasting?

Intermittent fasting means you eat only within certain time periods. This can help with weight loss because after a prolonged period without food, the body begins burning fat for energy. People are encouraged to drink water and other calorie-free beverages while fasting.

There are three common approaches to intermittent fasting:

• A time-restricted schedule means eating all of your meals within a certain time period — for example, skipping breakfast and eating only between 10 a.m. and 6 p.m.
• An alternate day schedule means fasting every other day. People eat normally on non-fasting days, and significantly restrict their calories the next day.
• The 5:2 approach means fasting two days per week and eating normally the other five days.

What does the research say about intermittent fasting?

There are significant benefits for your heart if intermittent fasting leads to healthy weight loss. Dr. Garg, who is also an associate professor of clinical medicine at the Keck School of Medicine of USC, says weight loss improves blood pressure, cholesterol levels, glucose tolerance and overall vascular health. He adds that it can also reduce inflammation and sleep apnea and enhance brain health.

As for potential risks, Dr. Garg says, “the main takeaway about intermittent fasting is we don’t have that much research on it.”

The preliminary study presented to the American Heart Association early in 2024 spurred renewed debate about intermittent fasting. The research team looked at more than 20,000 National Health and Nutrition Examination surveys from 2003 to 2018. The annual federal survey asks participants about their dietary patterns.

After comparing the results to death data from the Centers for Disease Control and Prevention, the team concluded that intermittent fasting led to a 91% increased risk of death from cardiovascular disease. Dr. Garg calls this research “thought-provoking, but certainly not definitive.”

He stresses that “it’s hard to draw any conclusions or figure out how to put the findings into context because this was based on people filling out a questionnaire. It may not be an accurate assessment of their typical eating patterns.”

He adds that since the study was retrospective, it’s difficult to determine causation versus correlation. A person who had a family history of heart disease, for example, was already at higher risk for serious heart problems. Whether that person tried intermittent fasting may not have been relevant.

Can intermittent fasting cause heart palpitations?

Severely restricting calories can lower blood sugar levels, which can cause heart palpitations, “If you’re not eating but you’re still active throughout the day, it’s possible your heart rate will go up,” Dr. Garg explains. “Your blood volume is reduced, so your body has to work harder.”

He says he wouldn’t recommend intermittent fasting for the following groups:

• Elderly people
• Children and growing teenagers
• Diabetics
• People with chronic conditions impacting their heart, kidney and liver
• Those suffering from an eating disorder

Dr. Garg says patients with diabetes, low blood pressure and people taking diuretics generally shouldn’t fast because it can trigger hypoglycemia, or low blood sugar. Hypoglycemia can lead to heart arrhythmias, increase heart rate and even cause a heart attack.

Patients with heart disease and those who have survived a heart attack need to be very careful about trying intermittent fasting, Dr. Garg says. “In general, you have to be cautious. They may have specific requirements for energy and need to eat throughout the day. They more be frailer and more prone to falls.”

Dr. Garg encourages patients to speak to a medical professional, like their primary care doctor or cardiologist, about whether their body can tolerate fasting. He also advises speaking to a nutritionist if you’re considering intermittent fasting.

“The fact is we don’t yet have long-term data on the sustainability of intermittent fasting,” Dr. Garg adds. “We have work to do to determine whether intermittent fasting will make it into the class of diets that are well established and trusted to be healthy.”

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