Impacts of Fasting on Cardiovascular Health

Fasting, an age-old practice rooted in various cultural, religious, and health traditions, has long been revered for its potential benefits to body and mind. Historically, fasting has been a means of spiritual purification and physical renewal, practiced by many societies around the world. In recent years, intermittent fasting has surged in popularity, capturing the attention of the health and wellness community. This modern iteration involves cycling between periods of eating and fasting and is praised for its purported benefits on weight management, metabolic health, and overall well-being. Intermittent fasting continues to gain traction as a versatile and effective dietary strategy for many who don’t want to subscribe to the more traditional methods for weight loss such as dieting and exercise.

To date, clinical studies have demonstrated that fasting can significantly improve insulin sensitivity, reducing the risk of type 2 diabetes and aiding in blood sugar control. Fasting has also been shown to lower blood pressure and improve cholesterol levels, thereby enhancing cardiovascular health. Additionally, fasting can reduce inflammation and oxidative stress, contributing to overall cellular health and potentially lowering the risk of chronic diseases.

However, research recently presented by the American Heart Association’s Epidemiology and Prevention│Lifestyle and Cardiometabolic Scientific Sessions 2024, March 18- 21, in Chicago provides a more cautionary approach to jumping on the fasting bandwagon. The AHA meeting offers the latest science on population-based health and wellness and implications for lifestyle. The surprising intermittent fasting findings were based on an analysis of over 20,000 U.S. adults and found some fasting resulted in a 91% higher risk of death from cardiovascular disease and questions short-term health benefits versus the longer-term negative impacts on cardiovascular health.

Summary of Findings

• A study of over 20,000 adults found that those who followed an 8-hour time-restricted eating schedule, a type of intermittent fasting, had a 91% higher risk of death from cardiovascular disease.

• Researchers report that people who practice this time-restricted eating plan also had poorer outcomes if they had existing cardiovascular disease or cancer.

• Among people with existing cardiovascular disease, an eating duration of no less than 8 but less than 10 hours per day was also associated with a 66% higher risk of death from heart disease or stroke.

• An eating duration of more than 16 hours per day was associated with a lower risk of cancer mortality among people with cancer.

• Compared with a standard schedule of eating across 12-16 hours per day, limiting food intake to less than 8 hours per day was not associated with living longer.

The analysis — which has not yet been peer-reviewed or published in an academic journal — is based on data from the Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey collected between 2003 and 2018. The researchers analyzed responses from around 20,000 adults who recorded what they ate for at least two days, then looked at who had died from cardiovascular disease after a median follow-up period of eight years. It’s some of the first research investigating the association between time-restricted eating (a type of intermittent fasting) and the risk of death from cardiovascular disease.

Intermittent fasting regimens vary widely. A common schedule is to restrict eating to a period of six to eight hours per day, which can lead people to consume fewer calories, though some eat the same amount in a shorter time. Another popular schedule is the "5:2 diet," which involves eating 500 to 600 calories on two nonconsecutive days of the week but eating normally for the other five.

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, said it’s not clear why his research found an association between time-restricted eating and a risk of death from cardiovascular disease. He offered an observation, “People who limited their eating to fewer than eight hours per day had less lean muscle mass than those who ate for 12 to 16 hours. Low lean muscle mass has been linked to a higher risk of cardiovascular death.”

Additionally, fasting can increase stress hormones such as cortisol and adrenaline, since the body doesn’t know when to expect food next and goes into survival mode. That added stress may raise the short-term risk of heart problems among vulnerable groups particularly elderly people or those with chronic health conditions.

Research Limitations

The new research has limitations: It relies on people’s memories of what they consumed over 24 hours and doesn’t consider the nutritional quality of the food they ate or how many calories they consumed during an eating window. The analysis was also narrowly focused looking at two days’ worth of data and drawing some very big conclusions from a very limited snapshot of a person’s lifestyle habits

The research highlights the need to consult with one’s physician before drastically changing one’s eating habits. 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 an increased risk of cardiovascular death. The 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. 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.

This study was observational, so it is hard to draw definitive conclusions, but it does add to the growing body of studies on the pros and cons of time-restricted eating.

ACLS Academy is an authorized American Heart Association (AHA)- Aligned Training Center with three convenient locations in Massachusetts: Quincy, Bridgewater, and Newton Center. ACLS Academy provides high-quality courses, all taught by instructors practicing in the medical profession, for ACLS, TNCC, BLS, ENPC, NRP, PALS, Bloodborne Pathogen, HeartSaver CPR/AED, First Aid, and Instructor Courses. Please browse our catalog of courses.