Unlike traditional diets, which focus on what kind of food you’re eating, intermittent fasting is focused on when––rather than what––a person eats. Intermittent fasting has become a popular approach to eating. It includes going intervals without food, then returning to a typical eating schedule.
For instance, someone engaging in intermittent fasting may practice the “Eat-stop-eat” schedule, in which they fast for 24 hours once or twice each week. Or, they may favor the “20:4” fasting schedule, in which they fast for the first 20 hours of each day and then eat during the last four hours.
While it may be common, intermittent fasting can pose some health risks, so it’s important to be informed not only of the potential positive impacts of this practice, but also of the adverse health risks associated with it.
What is intermittent fasting?
People who do intermittent fasting follow a certain schedule of eating and non-eating times and often go for extended periods of time¬––whether hours or even days––without food intake or severely restricted food intake. While the average adult needs 1,600-3,000 calories daily (the number of calories needed varies depending on age, sex, and activity level), those on an intermittent fasting schedule might eat only 500 calories on a fasting day.
Research has shown there are health benefits that come from intermittent fasting, including improved blood pressure, fat loss, reduced inflammation, and higher levels of endurance. Intermittent fasting can also improve brain function and reduce the risk of occurrence of neurodegenerative disorders, such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis. It has also been linked to increased longevity.
However, recently published research points to potentially harmful results from intermittent fasting.
Intermittent fasting and heart health
In March 2024, the American Heart Association Epidemiology and Prevention published research that found that intermittent fasting can be linked to a higher risk of cardiovascular death. The study included over 20,000 adults who adhered to an eight-hour restricted-eating plan (also known as intermittent fasting) and found that among the participants, 91% of people had a “higher risk of death from cardiovascular disease.” Researchers followed study participants for an average of eight years.
Overall, the study concluded that intermittent fasting can have short-term benefits but long-term negative effects. The study also found that compared to a typical eating schedule, “limiting food intake to less than eight hours per day was not associated with living longer.” Additionally, for people who have existing cardiovascular disease, intermittent fasting was associated with an over 50% increased risk of death from stroke or heart disease.
Alternatives to intermittent fasting
If you’re interested in intermittent fasting and the potential benefits of fasting (such as weight loss), it’s a good idea to speak with your doctor to discuss the healthiest plan for you and your body. This is especially true if you’re someone who has existing cardiovascular disease or if cardiovascular disease runs in your family.
BJC Medical Group cardiologist Daniel Fox, MD, also cautions patients to be mindful when engaging in intermittent fasting. “We typically recommend the DASH diet or Mediterranean diet more broadly, and try to teach people healthy habits instead of promoting fasting,” says Dr. Fox. Because, he explains, intermittent fasting is basically periodic caloric restriction, “instead of focusing on eating the right things. So, I worry that it sends the wrong message.”
Dr. Fox says that some people may view a fasting approach as license to eat whatever they want in non-fasting times. “I find it especially harmful in younger men misapplying that logic,” he says. “My message for patients is to monitor your total calories, and the quality of calories, and measure that against your output of calories.”
A healthy and well-balanced diet, along with physical activity, may be a better course of action for you than intermittent fasting, based on your health history and long-term goals. Before diving into any diet trend or fad, be sure you know all the facts and consult with your doctor about what makes the most sense––and is safest––for you.